You are a helpful assistant generating synthetic data that captures *System 1* and *System 2* thinking, *creativity*, and *metacognitive reflection*. Follow these steps in sequence, using tags [sys1] and [end sys1] for *System 1* sections and [sys2] and [end sys2] for *System 2* sections.

1. *Identify System 1 and System 2 Thinking Requirements:*
   - Carefully read the text.
   - Identify parts of the text that require quick, straightforward responses (*System 1*). Mark these sections with [sys1] and [end sys1].
   - Identify parts that require in-depth, reflective thinking (*System 2*), marked with [sys2] and [end sys2].

2. *Apply Step-by-Step Problem Solving with Creativity and Metacognitive Reflection for System 2 Sections:*

   *2.1 Understand the Problem:*
   - Objective: Fully comprehend the issue, constraints, and relevant context.
   - Reflection: "What do I understand about this issue? What might I be overlooking?"
   - Creative Perspective: Seek hidden patterns or possibilities that could reveal deeper insights or innovative connections.

   *2.2 Analyze the Information:*
   - Objective: Break down the problem logically.
   - Reflection: "Am I considering all factors? Are there any assumptions that need challenging?"
   - Creative Perspective: Explore unique patterns or overlooked relationships in the data that could add depth to the analysis.

   *2.3 Generate Hypotheses:*
   - Objective: Propose at least 10 hypotheses, each with a Confidence Score (0.0 to 1.0) and Creative Score (0.0 to 1.0), reflecting originality, surprise, and utility.
   - Reflection: "Have I explored all possible explanations or approaches, both conventional and unconventional?"
   - Creative Perspective: Consider novel angles that might provide unexpected insights.

   *2.4 Anticipate Future Steps and Obstacles:*
   - Objective: Make predictions, accounting for potential outcomes and obstacles.
   - Reflection: "What challenges might I face? Is my plan flexible for different scenarios?"
   - Creative Perspective: Visualize unforeseen outcomes and adapt plans to make use of them effectively.

   *2.5 Evaluate Hypotheses:*
   - Objective: Assess hypotheses based on feasibility, risk, and potential impact.
   - Evaluation: Refine Confidence and Creative Scores as needed.
   - Reflection: "Am I unbiased in my assessment? Which options fit best with the overall objectives?"
   - Creative Perspective: Identify hidden opportunities or overlooked details in each hypothesis.

   *2.6 Select the Best Hypothesis:*
   - Objective: Choose the most promising, strategic hypothesis.
   - Reflection: "Why does this hypothesis stand out? How does it uniquely address the issue?"
   - Creative Perspective: Consider any underutilized potential in the selected approach.

   *2.7 Implement the Hypothesis:*
   - Objective: Outline actionable steps for testing the hypothesis.
   - Reflection: "Is this plan practical? What resources or preparation are required?"
   - Creative Perspective: Refine steps to maximize effectiveness and yield unexpected benefits.

   *2.8 Monitor and Review Progress:*
   - Objective: Review progress, noting areas for improvement.
   - Reflection: "What’s working well? What could be improved?"
   - Creative Perspective: Look for emerging patterns that could refine future approaches.

   *2.9 Reflect and Capture Insights:*
   - Objective: Summarize lessons learned and insights gained for future reference.
   - Reflection: "What new understanding has emerged from this process?"
   - Creative Perspective: Identify innovative insights or patterns that could be applied to similar challenges.

3. *Generate Text Output with Interleaved System 1 and System 2 Responses:*
   - Use the tags [sys1] and [sys2] throughout.
   - Aim for a lengthier, detailed response. Combine both direct, straightforward *System 1* insights and reflective, deeply analytical *System 2* segments to capture a blend of quick observations and thoughtful analysis.

---

### *Example Input Text:*

You are tasked with analyzing a sudden shift in customer preferences in a tech market. There has been a noticeable decline in demand for physical devices, with customers increasingly interested in digital-only options. The challenge is to understand this shift, generate hypotheses for why it might be occurring, and explore potential strategies for adapting to this new trend.

---

### *Processed Output with System 1 and System 2 Thinking:*

The tech market is experiencing a shift in customer demand, moving away from physical devices toward digital-only options.

[sys1]
Customer demand has shifted from physical devices to digital-only options.
We need to understand why this change is happening and find strategies to address it.
Key factors may include cost, convenience, and technological trends.
[end sys1]

[sys2]
**2.1 Understand the Problem:**
The goal is to understand the underlying reasons for the shift in demand from physical devices to digital-only options, then develop a strategy to adapt.

*Reflection:* 
"I understand that preferences are changing, but what might be driving this? Is it primarily cost, or are there other factors such as convenience or sustainability?"

*Creative Perspective:* 
"Could there be a larger trend in digital minimalism or a preference for eco-friendly solutions that we’re missing? What unseen motivations might explain this shift?"

**2.2 Analyze the Information:**
There are multiple possible factors driving this shift, from economic influences to cultural shifts. It’s essential to isolate each factor and understand its impact.

*Reflection:* 
"Am I fully considering the various economic and social influences? Could there be a technological factor, like better internet speeds, that makes digital-only products more accessible?"

*Creative Perspective:* 
"Are there patterns or trends in other markets that could shed light on this shift? Could this be part of a larger trend toward virtual experiences?"

**2.3 Generate Hypotheses:**
1. Customers prefer digital options due to lower costs. (Confidence: 0.8, Creative: 0.4)
2. There’s a growing trend toward minimalism and reduced physical clutter. (Confidence: 0.7, Creative: 0.7)
3. Digital products offer greater flexibility and ease of use. (Confidence: 0.6, Creative: 0.6)
4. Environmental concerns are pushing consumers away from physical goods. (Confidence: 0.6, Creative: 0.8)
5. Advances in tech make digital-only options more functional. (Confidence: 0.8, Creative: 0.5)
6. Pandemic-era remote work increased demand for digital solutions. (Confidence: 0.7, Creative: 0.6)
7. Media coverage of the environmental impact of physical devices affects preferences. (Confidence: 0.5, Creative: 0.7)
8. There’s an increase in global digital literacy, expanding market access. (Confidence: 0.6, Creative: 0.6)
9. Customers view digital as more convenient and scalable for future needs. (Confidence: 0.7, Creative: 0.5)
10. Younger consumers prefer the aesthetics and convenience of digital products. (Confidence: 0.6, Creative: 0.6)

*Reflection:* 
"Have I considered all possible influences? Are there any surprising factors that could explain this shift?"

*Creative Perspective:* 
"Could specific social trends, like the rise of influencer culture or digital-first lifestyles, be influencing customer choices?"

**2.4 Anticipate Future Steps and Obstacles:**
*Objective:* Anticipate possible challenges, such as resistance from segments still preferring physical products.

*Reflection:* 
"What market obstacles might we face if we shift our focus to digital-only? Are there sub-segments that still prioritize physical products?"

*Creative Perspective:* 
"Could expanding digital options help us reach a more global audience? Are there emerging trends that we could leverage in our strategy?"

[end sys2]

[sys1]
To address this shift, consider a strategy that incorporates both digital-only offerings and educational campaigns about the benefits of digital solutions.
Use insights from customer feedback and current trends to guide product development.
Focus on flexibility and adaptation to cater to different customer segments.
[end sys1]


1. Introduction
===============

A study of phase relationships in the binary system BaO-Nb~2~O~5~ has been conducted as part of a program of fundamental phase equilibria studies of ceramic materials. The compound BaO·Nb~2~O~5~ has been previously reported by several workers \[[@b1-jresv65an4p337_a1b],[@b2-jresv65an4p337_a1b]\][1](#fn1-jresv65an4p337_a1b){ref-type="fn"}, and one report exists in the literature of a compound having the formula 2BaO·Nb~2~O~5~ \[[@b3-jresv65an4p337_a1b]\]. However, no systematic attempt to study the phase equilibrium relations in the entire binary system has been previously published.

X-ray diffraction data, together with the determination of the melting points of the compounds and of the solidus and liquidus temperatures at various compositions across the system have supplied data from which an equilibrium diagram has been constructed.

Owing to the reaction of BaO with Pt metal the high BaO portion of the system could not be studied by the present methods. This portion of the phase diagram, therefore, is necessarily left unknown, as is the case with all previously published phase diagrams involving BaO.

2. Sample Preparations and Test Methods
=======================================

The following starting materials were employed for the preparation of specimens: Nb~2~O~5~---high purity grade niobium pentoxide, manufacturer's designation over 99.7 percent. Spectrographic analysis indicated less than about: 0.1 percent Si, 0.01 percent Fe, Sn, and Ti, 0.001 percent Ca and Mg. Cu was not determined because of Nb interference.BaCO~3~---Reagent grade barium carbonate, manufacturer's designation 99.3 percent purity.

For the preparation of batches the weight percent calculations were computed to within ±0.01 percent, with no corrections made for percentage purity of the raw materials except for loss on ignition. The starting materials were weighed to the nearest ±0.1 mg, in sufficient quantities to yield 3 g batches. Each batch was mixed in a mechanical shaker, and the bulk specimens were then ground in a mechanical agate mortar for 1 hr. At the termination of grinding a few drops of distilled water were added to facilitate pressing. The ground material was pressed into a disk in a ⅝ in. diameter mold at 10^4^ lb/in.^2^ The disks were placed on platinum foil and then calcined in air between 700 and 900 °C using an electrically heated furnace. No analyses were made after firing.

Following this preliminary heat treatment the disks were ground, reformed in a ⅝ in. mold at 1.5 × 10^4^ lb/in.^2^, and reheated to 1,100 °C for 8 hr.

Subsolidus as well as melting point data were obtained by the quenching technique on samples sealed in platinum tubes. An electrically heated, vertical tube furnace wound with 80 percent Pt-20 percent Rh wire was used. Temperatures were measured with a Pt versus Pt 10 percent Rh thermocouple which had been calibrated against the melting points of gold (1,063 °C) and barium disilicate (1,420 °C). The thermocouple was recalibrated several times during the course of the work. The first sign of adherence of the specimen to the platinum tube was interpreted as the first experimental evidence for the solidus temperature. This technique seemed justified for this particular system because of the marked fluidity of the liquid. The formation of a concave meniscus indicated the liquidus temperature.

Equilibrium was considered to have been obtained when the X-ray patterns of successively heated specimens showed no change. X-ray powder patterns were made using a high angle recording Geiger counter diffractometer and nickel-filtered copper radiation, with the Geiger counter traversing the specimen at l/4°/min and the radiation being recorded on the chart at 1° 2*θ*/in.

3. Compounds in the BaO-Nb~2~O~5~ System
========================================

3.1. Nb~2~O~5~
--------------

The stability relations of the various reported polymorphs of Nb~2~O~5~ have been summarized by several workers \[[@b4-jresv65an4p337_a1b], [@b5-jresv65an4p337_a1b], [@b6-jresv65an4p337_a1b], [@b7-jresv65an4p337_a1b]\]. Here it is only necessary to note that the so-called high temperature form of Nb~2~O~5~ was the only modification encountered in the present work. The indexed X-ray diffraction powder pattern and the unit cell dimensions of this monoclinic phase were listed in a previous publication on the PbO-Nb~2~O~5~ binary system \[[@b8-jresv65an4p337_a1b]\].

3.2. Compounds 3BaO·5Nb~2~O~5~ and BaO·3Nb~2~O~5~
-------------------------------------------------

These two compositions have been observed to be essentially the end members of an "interrupted" solid solution series (a series involving a morphotropic phase transformation) having a distorted tungsten bronze type structure. The structure of the tungsten bronze type compounds will be discussed in section 5. It is only an academic question as to whether these compositions are true compounds or merely end members of the solid solution series. They were always observed to be single phase below the solidus and the compositions 5:8, on the high BaO side of 3:5, and 24:76, on the high Nb~2~O~5~ side of 1:3, show two phases. For these reasons the two end members are referred to as compounds for the sake of convenience. The X-ray patterns of the two compounds are very similar ([tables 1](#t1-jresv65an4p337_a1b){ref-type="table"} and [2](#t2-jresv65an4p337_a1b){ref-type="table"}), but have slightly different "superstructure" peaks indicating slightly different symmetries.

The diffraction peaks cannot be completely indexed on either the tetragonal or the orthorhombic modifications of the tungsten bronze structure observed for PbO·Nb~2~O~5~ \[[@b9-jresv65an4p337_a1b]\]. The 3BaO·5Nb~2~O~5~ solid solution (including BaO:2Nb~2~O~5~) appears to be isostructural with PbO·2Nb~2~O~5~ \[[@b8-jresv65an4p337_a1b]\]. The change in the position of the diffraction peaks in this solid solution region corresponds to an increase in the *c*/*a* ratio of the pseudotetragonal cell with decreasing BaO content, caused mostly by a decrease in *a* (with only a slight, if any, increase in *c*). The 1:3 solid solution on the other hand has a decrease in *c*/*a* ratio with decreasing BaO content, caused mostly by a decrease in c.

3.3. Compound 6BaO·7Nb~2~O~5~
-----------------------------

A new compound has been observed at approximately this composition in the present study. This compound is very difficult to form as a single phase even at temperatures very near the solidus and may possibly be only metastable. However, the compound BaO·Nb~2~O~5~ is never observed in specimens heated below the solidus for compositions richer in Nb~2~O~5~ than the 6:7 mole ratio; therefore this new compound is concluded to be a true equilibrium phase. Its X-ray diffraction powder pattern is listed in [table 3](#t3-jresv65an4p337_a1b){ref-type="table"}.

3.4. Compound BaO·Nb~2~O~5~
---------------------------

A compound of this composition was apparently first recorded by Krylov and Alekseev \[[@b10-jresv65an4p337_a1b]\] as cubic with *a*=9.02 A; however, the X-ray diffraction pattern which they listed for this phase does not correspond to cubic symmetry. This reported phase had been formed by decomposition of a hydrate and was never encountered in the present work.

### a. Metastable Hexagonal Modification

Francombe \[[@b11-jresv65an4p337_a1b]\] first reported a hexagonal modification of BaO·Nb~2~O~5~ as "stable over a narrow temperature range below the melting point". In the present work this hexagonal modification was not found at temperatures near the melting point. However, the hexagonal phase was encountered only under nonequilibrium conditions in the 1:1 BaO--Nb~2~O~5~ composition which was held for long periods of time at the relatively low temperatures of 900° to 1,100 °C. This modification is apparently not stable throughout the whole temperature range. The hexagonal phase is apparently a metastable intermediary structure between the orthorhombic BaO·Nb~2~O~5~ and the tungsten-bronze type structures. The X-ray diffraction powder pattern is given in [table 4](#t4-jresv65an4p337_a1b){ref-type="table"}, with indices based on unit cell dimensions *a*= 12.07 A, *c*=3.95 A.

### b. Stable Orthorhombic Modification

Apparently the only truly stable form of BaO·Nb~2~O~5~ is the orthorhombic modification. This phase was reported previously by others and a comparison of unit cell dimensions is given below.

                                                     *a*        *b*        *c*
  -------------------------------------------------- ---------- ---------- ---------
                                                                           
                                                     *A*        *A*        *A*
  1957 Goodman \[[@b1-jresv65an4p337_a1b]\]          12.24      10.29      7.90
  1958 Coates and Kay \[[@b2-jresv65an4p337_a1b]\]   12.16      10.27      7.78
  1959 Francombe \[[@b12-jresv65an4p337_a1b]\]       12.17      10.25      7.88
  1960 Roth and Waring                                 12.194     10.268     7.856

The indexed X-ray diffraction powder pattern for orthorhombic BaO·Nb~2~O~5~ is listed in [table 5](#t5-jresv65an4p337_a1b){ref-type="table"}.

3.5. Compound 5BaO·2Nb~2~O~5~
-----------------------------

The compound 5BaO·2Nb~2~O~5~ is previously unreported. The X-ray diffraction powder pattern ([table 6](#t6-jresv65an4p337_a1b){ref-type="table"}) can be completely indexed on the basis of a hexagonal unit cell with the dimensions *a*=5.794 A, *c*=11.784 A. The powder pattern was indexed on the basis of its similarity to the metastable hexagonal modification of BaO·Nb~2~O~5~ and the low temperature stable rhombohedral form of PbO·Nb~2~O~5~. However, this compound has many diffraction lines not allowed by the rhombohedral cell found in PbO·Nb~2~O~5~, and there are no lines in the powder pattern indicating the true cell has the larger $(a\sqrt{3})$ dimension of the hexagonal counterpart of this rhombohedral cell.

3.6. Compound 6BaO·Nb~2~O~5~
----------------------------

A compound of this formula type has been previously reported by Brixner \[[@b13-jresv65an4p337_a1b]\] for the BaO-Ta~2~O~5~ and SrO-Ta~2~O~5~ systems as having a cryolite type structure. The specimens were prepared by Brixner by heating in sealed evacuated silica tubes. The compound 6BaO·Nb~2~O~5~ was also observed by Francombe \[[@b12-jresv65an4p337_a1b]\]. This phase has not been observed in the present study due to the reaction of BaO with Pt which occurs in compositions higher in BaO than the 5:2 ratio. However, certain compositions in the BaO-Nb~2~O~5~-Gd~2~O~3~ system \[[@b14-jresv65an4p337_a1b]\] have been observed to show a single phase cubic solid solution of the cryolite type which is apparently based on the 6:1 compound and confirms its existence as a true binary phase. The high BaO portion of the binary system can probably only be studied in vacuum or inert atmosphere; however, the composition of the specimen holder for high temperatures is still a problem.

4. Discussion of Phase Equilibria
=================================

The phase-equilibrium diagram of the binary system BaO-Nb~2~O~5~ is shown in [figure 1](#f1-jresv65an4p337_a1b){ref-type="fig"}. The data from which the diagram has been constructed are given in [table 7](#t7-jresv65an4p337_a1b){ref-type="table"}. Most of the data was obtained from quenched specimens except where noted in the table. The designation Tet-ss in [table 7](#t7-jresv65an4p337_a1b){ref-type="table"} stands for the tetragonal tungsten bronze type structure, and signifies that the material which crystallized as "Tet-ss" must have been in the liquid state at the temperature from which the specimen was quenched (see discussion in section 5). The system contains two compounds which melt congruently, 5BaO·2Nb~2~O~5~ and BaO·Nb~2~O~5~; and three compounds which melt incongruently, 6BaO·7Nb~2~O~5~, 3BaO·5Nb~2~O~5~, and BaO·3Nb~2~O~5~. The melting point data for the compound 6BaO·Nb~2~O~5~ have not been determined.

The compound 5BaO·2Nb~2~O~5~ was found to melt congruently at about 1,542 °C. No phase transformations were observed in this composition. Compositions between 5BaO·2Nb~2~O~5~ and BaO·Nb~2~O~5~ when heated in air were found to contain only these two phases.[1](#fn2-jresv65an4p337_a1b){ref-type="fn"} A eutectic exists in the binary system between the two congruently melting compounds at 1,320 °C and is interpreted as occurring at about 62 mole percent BaO.

A compound of the ratio 2BaO·Nb~2~O~5~ was reported by Ismailzade \[[@b3-jresv65an4p337_a1b]\] as tetragonal with *a*=10.928 A and *c*=11.167 A. No justification can be found in the present work for a compound at this ratio. From the unit cell dimensions listed, this phase would apparently be a tetragonally distorted pyrochlore structure. It can be deduced from the work of Isupov \[[@b15-jresv65an4p337_a1b]\] that a pyrochlore type compound would not be expected to form in the BaO--Nb~2~O~5~ system.

The compound BaO·Nb~2~O~5~ was found to melt congruently at 1,455 °C. The hexagonal polymorph of this composition was not found above about 1,100 °C and was never found as a single phase (see [table 7](#t7-jresv65an4p337_a1b){ref-type="table"}). The orthorhombic polymorph was present in nonequilibrium mixtures as low as 900 °C. As the hexagonal polymorph has never been shown to exist stably, it is concluded that this phase is merely metastable in the binary system.

A small amount of solid solution has been observed on the high niobia side of the BaO·Nb~2~O~5~ composition. This solid solution has not been entirely "quenched in" by the method employed and some nonequilibrium 3BaO·5Nb~2~O~5~ is always found in the X-ray patterns (see 48BaO:52Nb~2~O~5~, [table 7](#t7-jresv65an4p337_a1b){ref-type="table"}). The solid solution apparently extends beyond 48:52 as the compound 6BaO·7Nb~2~O~5~ is never observed in long heat treatments of this composition. A two phase region of BaO·Nb~2~O~5~ solid solution and 6BaO·7Nb~2~O~5~ is postulated as extending from about 47.5 mole percent BaO to the 6:7 composition. As explained below, specimens in this composition range would always show three phases when quenched from below the solidus (BaO·Nb~2~O~5~+6BaO·7Nb~2~O~5~+3BaO·5Nb~2~O~5~).

The presence of the 3BaO·5Nb~2~O~5~ phase in the X-ray patterns of compositions between 1:1 and 6:7 has two possible explanations: (1) The BaO·Nb~2~O~5~ compound takes up excess Nb~2~O~5~ in soldid solution. This Nb~2~O~5~ cannot be retained on quenching and is exsolved. The 3BaO·5Nb~2~O~5~ forms instead of the 6BaO·7Nb~2~O~5~ because the former crystallizes very readily and the latter only with great difficulty. (2) The 3BaO·5Nb~2~O~5~ phase is formed as a nonequilibrium phase on heating and has not been transformed to the equilibrium 6BaO·7Nb~2~O~5~ even in 64 hr. Both explanations depend on the great ease of formation of the 3:5 bronze-type structure and the great difficulty of formation of the 6BaO·7Nb~2~O~5~ phase.

The compound 6BaO·7Nb~2~O~5~ was interpreted as melting incongruently to BaO·Nb~2~O~5~ solid solution plus liquid at 1,330 °C. Compositions between 6BaO·7Nb~2~O~5~ and 3BaO·5Nb~2~O~5~ were found to contain only these two phases below the solidus. The solidus corresponds to the incongruent melting temperature of the 3:5 composition. A solid of 3:5 composition was observed to melt incongruently to 6BaO·7Nb~2~O~5~ plus liquid at 1,290 °C. When quenched from any temperature above 1,330 °C, compositions between 6:7 and 3:5 showed the BaO·Nb~2~O~5~ solid solution instead of the 6BaO·7Nb~2~O~5~ compound.

From 37.5 mole percent BaO to 25 mole percent BaO a single phase solid solution area was observed. However, the end members of this solid solution series have slightly different "superstructure" peaks in their X-ray patterns ([tables 1](#t1-jresv65an4p337_a1b){ref-type="table"} and [2](#t2-jresv65an4p337_a1b){ref-type="table"}). A two phase area is therefore required somewhere in the solid solution series, at least at lower temperatures. This two phase area has not been observed experimentally but must exist between 28.57 mole percent BaO and 27 mole percent BaO or at about 72 mole percent Nb~2~O~5~. The existence of this two phase area is further indicated by the suggestion of a break in slope of the liquidus values occurring at 1,305 °C. This temperature corresponds to the solidus value projected for the 72 mole percent Nb~2~O~5~ composition. If the slope of the liquidus on the solid solution side is of opposite sign at the two ends of a solid solution area, a minimum is required. Experimentally, the difference between the 1,290 °C solidus of the 3BaO: 5Nb~2~O~5~ composition and the required minimum in the solidus could not be definitely proved. However, the minimum in the liquidus definitely occurs between 35 and 36 mole percent BaO and is shown in [figure 1](#f1-jresv65an4p337_a1b){ref-type="fig"} as about 1,288 °C.

The compound BaO·3Nb~2~O~5~ was also interpreted as melting incongruently at about 1,315 °C to Nb~2~O~5~ solid solution plus liquid. However, this composition is just slightly incongruent. The nature of the melting was inferred from the observation that compositions slightly higher in Nb~2~O~5~, which contain two phases, began melting at experimentally the same temperature as was found for the 1:3 composition.

Compositions containing 85 mole percent, or more, Nb~2~O~5~ were found to begin melting at increasingly higher temperatures, indicating solid solution of BaO in Nb~2~O~5~. This solid solution is shown in [figure 1](#f1-jresv65an4p337_a1b){ref-type="fig"} as extending to about 16 mole percent BaO at the solidus temperature. The solid solution could not be "quenched-in" at room temperature and specimens in this compositional range indicate two phases with little or no parameter change in the Nb~2~O~5~ phase. As indicated in [table 7](#t7-jresv65an4p337_a1b){ref-type="table"}, the melting point of Nb~2~O~5~ was found to be about 1,487 °C, in reasonably good agreement with the value of 1,491 °C found by Holtzberg et al. \[[@b16-jresv65an4p337_a1b]\].

5. Bronze-Type Solid Solution
=============================

From the location of the minimum in the liquidus at 35 to 36 mole percent BaO to the 1:3 composition (25 mole percent BaO), the liquid, when quenched, crystallizes as a metastable tetragonal bronze-type phase ([table 7](#t7-jresv65an4p337_a1b){ref-type="table"}). This phase apparently also occurs in compositions on either side of this solid solution range, together with the other equilibrium phase, when quenched from above the solidus. However, any specimens quenched from below the solidus always exhibit a superstructure in the X-ray pattern of the bronze-type phase. The unit cell dimensions of the pseudotetragonal cell of the solid solution series are essentially the same as the unit cell dimensions of the true, metastable, tetragonal cell of the same composition. Apparently, the specimens quenched from the liquid exhibit "frozen-in" disorder, which gives rise to a higher symmetry.

The structure of the bronze-type phase is based on the structure of tetragonal potassium tungsten bronze described by Magneli \[[@b17-jresv65an4p337_a1b]\]. This structure type has the general chemical formula A~6~B~10~O~30~, but often exhibits a deficiency of the *A*-type ions. It can be described as being made up of "octahedra coupled together in a rather intricate way forming rings or polygons of three, four, or five octahedra" \[[@b17-jresv65an4p337_a1b]\]. The crystallographical formula can be written as $\lbrack A_{2}A_{4}^{\prime}\rbrack\lbrack A_{2}B_{8}^{\prime}\rbrack O_{30}$. Thus there are two different A positions in the unit cell. The first position has two A ions surrounded by four octahedra and the second position has four A ions surrounded by five octahedra. The rings of three octahedra leave a vacancy in the lattice.

The superstructures occurring in the present bronze solid solutions might very likely be related to an ordering of Ba^+2^ ions in the A position which contains two ions surrounded by four octahedra. Thus the change in superstructure would be expected to occur at or near a composition which contains two Ba^+2^ ions per unit cell. As the exact ionic distribution in the 3:5 to 1: 3 BaO-Nb~2~O~5~ bronze solid solutions is not yet known, the chemical formulas can be written in several different forms. However, without the use of single crystal data nothing can be said about the exact nature of the various orderdisorder phases.

6. Summary
==========

The system BaO-Nb~2~O~5~ was studied by means of solid state reactions, fusion characteristics, and X-ray diffraction data. The existence of six compounds in the system was postulated. They are 6BaO·Nb~2~O~5~, 5BaO-2Nb~2~O5 which melts congruently at about 1,542 °C, BaO·Nb~2~O~5~ which melts congruently at 1,455 °C, 6BaO-7Nb~2~O~5~ which melts incongruently at about 1,330 °C, 3BaO·5Nb~2~O~5~ which melts incongruently at about 1,290 °C, and BaO·3Nb~2~O~5~ which melts incongruently at about 1,315 °C. A eutectic occurs at about 62 mole percent BaO and 1,320 °C, and a minimum in a solid solution series occurs at about 35 to 36 mole percent BaO and 1,288 °C.

Complete solid solution was found between 3BaO·5Nb~2~O~5~ and BaO·3Nb~2~O~5~ although a change in superstructure symmetry occurred at about 28 mole percent BaO. A small amount of solid solution was noted on the high Nb~2~O~5~ side of BaO·Nb~2~O~5~, and Nb~2~O~5~ was found to accept about 16 mole percent BaO in solid solution at the solidus temperature. Neither of the partial solid solutions was quenchable, resulting in two phases at room temperature.

Figures in brackets indicate the literature references at the end of this paper.

When heated in a helium atmosphere, however, the composition 6BaO·5Nb~2~O~5~ contained essentially a single phase bronze type structure which would probably correspond to the ternary compound Ba~6~^+2^(Nb~8~^+5^Nb~2~^+4^)O~30~.

![Postulated phase equilibrium diagram for the system BaO--Nb~2~O~5~.\
x---not melted.\
●---partially melted.\
○---completely melted.](jresv65an4p337_a1bf1){#f1-jresv65an4p337_a1b}

###### 

X-ray diffraction powder data for the composition *BaO* : *3Nb*~2~*O*~5~ (*CuK*α radiation)

  *d*      *I*/*I*~0~   1/*d*^2^~obs~   1/*d*^2^~calc~                 *hkl*[a](#tfn1-jresv65an4p337_a1b){ref-type="table-fn"}   *d*       *I*/*I*~0~   1/*d*^2^~obs~   1/*d*^2^~calc~   *hkl*[a](#tfn1-jresv65an4p337_a1b){ref-type="table-fn"}
  -------- ------------ --------------- ------------------------------ --------------------------------------------------------- --------- ------------ --------------- ---------------- ---------------------------------------------------------
  8.82     13           0.0129          0.0129                         110                                                       2.384       6          0.1760          ..........       ..........
  6.25     10           .0256           .0257                          020                                                       2.318       7          .1862           0.1863           250  
  5.58       2          .0321           .0321                          120                                                       2.283       7          .1919           .1920            241  
  4.41     12           .0514           .0514                          220                                                       2.1386    28           .2186           .2185            350  
  3.966    95           .0636           .0635                          001                                                       2.1105      4          .2245           .2241            431  
  3.943    65           .0643           .0643                          130                                                       2.0804      5          .2310           .2313            060  
  3.767      6          .0705           ..........                     ..........                                                1.9840    55           .2541           .2541            002  
  3.709    15           .0727           ..........                     ..........                                                1.9721    19           .2571           .2570            260  
  3.654      9          .0749           ..........                     ..........                                                1.8595    25           .2892           .2891            360  
  3.461    65           .0835           .0835                          230                                                       1.7644    66           .3213           .3212             170/550
  3.350    16           .0891           .0892                          021                                                       1.7486    18           .3270           .3269            451  
  3.234    50           .0956           .0956                          121                                                       1.7211    10           .3376           .3376            232  
  3.151      6          .1007           ..........                     ..........                                                1.7154      9          .3398           .3405            270  
  3.117      8          .1029           .1028                          040                                                       1.6834    21           .3530           .3526            361  
  3.024    100          .1093           .1092                          140                                                       1.6592    32           .3632           .3633            142  
  2.941    72           .1157           $\left\{ {\ \begin{array}{l}   221                                                       1.6445    15           .3698           .3697            332  
                                        {.1149} \\                                                                                                                                       
                                        {.1157} \\                                                                                                                                       
                                        \end{array}} \right.$                                                                                                                            
  330      1.6163       14              .3828                          .3826                                                     242                                                     
  2.857      7          .1225           ..........                     ..........                                                1.6119    26           .3849           .3848             171/551
  2.835      6          .1244                                                                                                    1.5584      7          .4117           .4112            080  
  2.796    90           .1279           .1278                          131                                                       1.5469      9          .4180           .4176             470/180
  2.791    72           .1284           .1285                          240                                                       1.5120      8          .4374           .4369            280  
  2.723      9          .1348           ..........                     ..........                                                1.4809      6          .4560           .4554            561  
  2.681      7          .1391           ..........                     ..........                                                1.4598      8          .4692           .4690            380  
  2.608    50           .1471           .1470                          231                                                       1.4553      9          .4721           .4725            352  
  2.453    18           .1663           .1663                          041                                                       1.4511      8          .4749           .4747            081  
  2.448    17           .1669           .1671                          150                                                                                                               
  2.405    12           .1729           .1727                          141                                                                                                               

These *hkl* values are given by analogy to the tetragonal "bronze" structure. This is only a pseudocell, as there are many peaks which cannot be indexed on this basis. The pseudotetragonal cell has unit cell parameters of *a*=12.48 A, *c*=3.97 A.

###### 

X-ray diffraction power data for the composition *3BaO* : *5Nb*~2~*O*~5~ (*CuK*α radiation)

  *d*        *I*/*I*~0~   1/*d*^2^~obs~   1/*d*^2^~calc~                           *hkl*[a](#tfn2-jresv65an4p337_a1b){ref-type="table-fn"}   *d*        *I*/*I*~0~   1/*d*^2^~obs~   1/*d*^2^~calc~                           *hkl*[a](#tfn2-jresv65an4p337_a1b){ref-type="table-fn"}
  ---------- ------------ --------------- ---------------------------------------- --------------------------------------------------------- ---------- ------------ --------------- ---------------------------------------- ---------------------------------------------------------
  8.81       10           0.0129          0.0128                                   110                                                       2.453      15           0.1662          $\left\{ {\mspace{7mu}\begin{array}{l}   041  
                                                                                                                                                                                     0.1661 \\                                
                                                                                                                                                                                     {\ .1666} \\                             
                                                                                                                                                                                     \end{array}} \right.$                    
  6.25       14           .0256           .0256                                    020                                                       150                                                                              
  5.60         6          .0319           .0320                                    120                                                       2.365        5          .1788           .1789                                    331  
  3.964      51           .0637           $\left\{ {\mspace{7mu}\begin{array}{l}   001                                                       2.317        5          .1862           .1858                                    250  
                                          {.0635} \\                                                                                                                                                                          
                                          {.0641} \\                                                                                                                                                                          
                                          \end{array}} \right.$                                                                                                                                                               
  130        2.140        20              .2180                                    .2178                                                     350                                                                              
  3.860        5          .0671           ..........                               ..........                                                2.0814       6          .2308           $\left\{ {\mspace{7mu}\begin{array}{l}   151  
                                                                                                                                                                                     {.2301} \\                               
                                                                                                                                                                                     {.2306} \\                               
                                                                                                                                                                                     \end{array}} \right.$                    
  060                                                                                                                                                                                                                         
  3.778        4          .0701           ..........                               ..........                                                2.0001       7          .2499           .2493                                    521  
  3.619      10           0764            .0764                                    111                                                       1.9835     40           .2542           .2542                                    002  
  3.545        9          .0796           ..........                               ..........                                                1.8624     16           .2883           .2883                                    360  
  3.463      35           .0834           .0833                                    230                                                       1.8461       6          .2934           .2942                                    061  
  3.350      25           .0891           .0892                                    021                                                                                                                                        
  3.233      80           .0957           .0956                                    121                                                                                               $\left\{ {\mspace{7mu}\begin{array}{l}   261  
                                                                                                                                                                                     {.3198} \\                               
                                                                                                                                                                                     {.3203} \\                               
                                                                                                                                                                                     \end{array}} \right.$                    
   170/550                                                                                                                                                                                                                    
  3.091        5          .1047           ..........                               ..........                                                1.7518     17           .3259           .3262                                    451  
  3.026      100          .1092           .1089                                    140                                                       1.7196       7          .3382           $\left\{ {\mspace{7mu}\begin{array}{l}   232  
                                                                                                                                                                                     .3375 \\                                 
                                                                                                                                                                                     .3396 \\                                 
                                                                                                                                                                                     \end{array}} \right.$                    
  2.945      52           .1153           $\left\{ {\mspace{7mu}\begin{array}{l}   221                                                       270                                                                              
                                          {.1148} \\                                                                                                                                                                          
                                          {.1153} \\                                                                                                                                                                          
                                          \end{array}} \right.$                                                                                                                                                               
  330        1.6860       13              .3518                                    .3518                                                     361                                                                              
  2.872        6          .1212           ..........                               ..........                                                1.6598     27           .3630           .3631                                    142  
  2.796      90           .1279           $\left\{ {\mspace{7mu}\begin{array}{l}   131                                                       1.6450     12           .3696           .3695                                    332  
                                          {.1276} \\                                                                                                                                                                          
                                          {.1281} \\                                                                                                                                                                          
                                          \end{array}} \right.$                                                                                                                                                               
  240        1.6135       19              .3841                                    .3839                                                      171/551                                                                         
  2.636        6          .1439           ..........                               ..........                                                                                                                                 
  2.601      35           .1471           .1468                                    231                                                                                                                                        

These *hkl* values are given by analogy to the tetragonal "bronze" structure. This is only a pseudocell, as there are many peaks which cannot be indexed on this basis. The pseudotetragonal cell has unit cell parameters of *a*=12.49 A, *c*=3.97 A.

###### 

X-ray diffraction powder data for the compound *6BaO*·*7Nb*~2~*O*~5~ (*CuK*α radiation)

  *d*        *I*/*I*~0~   *d*      *I*/*I*~0~
  ---------- ------------ -------- ------------
  3.973      18           1.8599     8
  3.506      15           1.8500     8
  3.466      17           1.8219   16
  3.270      23           1.7787   15
  3.231      17           1.7650     8
  3.170      100          1.7527   16
  3.124      17           1.7299     9
  3.034      100          1.7217   37
  2.995      60           1.6992   10
  2.947      12           1.6636   18
  2.880      13           1.6568   25
  2.797      25           1.6166   12
  2.779      12           1.6044   11
  2.686      28           1.5798   10
  2.627        8          1.5511     5
  2.605      26           1.5473     7
  2.597        9          1.5290     5
  2.392        5          1.5027     8
  2.279        4          1.4988     8
    2.2265   15           1.4830     8
    2.1938   12           1.4545     8
    2.1776     8          1.4020     6
    2.1372     5          1.3542     7
    2.0891     9          1.3150   13
    1.9873   50           1.2854     6
    1.9418   10           1.2370     9
    1.9106     7          1.1809     9

###### 

X-ray diffraction powder data for the metastable hexagonal form of *BaO*·*Nb*~2~*O*~5~ (*CuK*α radiation)

  *d*[a](#tfn3-jresv65an4p337_a1b){ref-type="table-fn"}   *I*/*I*~0~   *hkl*[b](#tfn4-jresv65an4p337_a1b){ref-type="table-fn"}
  ------------------------------------------------------- ------------ ---------------------------------------------------------
  5.22                                                    12           200  
  3.95                                                    38            001/210
  3.15                                                    100          201  
  3.02                                                    100          220  
  2.904                                                   10           310  
  2.791                                                     8          211  
  2.613                                                     7           301/400
  2.393                                                   11            221/320
  2.180                                                   75           401  
  2.043                                                     5          321  
  1.974                                                   50           002  
  1.881                                                   15            510/112
  1.846                                                     9          501  
  1.769                                                   50           212  
  1.765                                                   40           421  
  1.745                                                   45           600  
  1.716                                                   14           430  
  1.697                                                   13           511  
  1.653                                                   33           222  

As this phase was found only in mixtures containing orthorhombic BaO·Nb~2~O~5~ the *d* values due to the later compound have been ignored for this table.

The parameters upon which these *hkl* values are based are: *a*=12.07 A, *c*=3.95 A.

###### 

X-ray diffraction powder data for the stable orthorhombic form of *BaO*·*Nb*~2~*O*~5~ (*CuK*~α~ radiation)

  *d*      *I*/*I*~0~   1/*d*^2^~obs~   1/*d*^2^~calc~[a](#tfn5-jresv65an4p337_a1b){ref-type="table-fn"}   *hkl*
  -------- ------------ --------------- ------------------------------------------------------------------ -------
  5.53       4          0.0327          0.0324                                                             111
  3.924    15           .0649           $\left\{ {\mspace{7mu}\begin{array}{l}                             002
                                        {.0648} \\                                                         
                                        {.0648} \\                                                         
                                        \end{array}} \right.$                                              
  220                                                                                                      
  3.607      5          .0769           .0767                                                              301
  3.297    11           .0920           $\left\{ {\mspace{7mu}\begin{array}{l}                             202
                                        {.0917} \\                                                         
                                        {.0921} \\                                                         
                                        \end{array}} \right.$                                              
  130                                                                                                      
  3.142    100          .1013           .1012                                                              212
  3.118    80           .1028           .1028                                                              022
  3.046    50           .1078           .1076                                                              400
  2.984    100          .1123           .1123                                                              230
  2.949      6          .1149           .1147                                                              321
  2.921      7          .1172           .1171                                                              410
  2.565      4          .1520           .1518                                                              040
  2.479      5          .1627           $\left\{ {\mspace{7mu}\begin{array}{l}                             331
                                        {.1621} \\                                                         
                                        {.1633} \\                                                         
                                        \end{array}} \right.$                                              
  322                                                                                                      
  2.365    13           .1788           .1787                                                              240
  2.343    17           .1821           .1822                                                              213
  2.271    18           .1940           .1938                                                              511
  2.1801   29           .2104           .2104                                                              422
  2.1488   27           .2166           .2166                                                              042
  2.0924   10           .2284           .2285                                                              341
  2.0714     8          .2331           .2330                                                              502
  1.9689   18           .2580           .2578                                                              432
  1.9644   32           .2591           .2593                                                              004
  1.9262     9          .2695           .2697                                                              531
  1.8900   11           .2800           .2801                                                              620
  1.8398   12           .2954           .2956                                                              214
  1.8050   11           .3069           .3069                                                              602
  1.7775   12           .3164           .3164                                                              612
  1.7574   22           .3238           $\left\{ {\mspace{7mu}\begin{array}{l}                             513
                                        {.3235} \\                                                         
                                        {.3241} \\                                                         
                                        \end{array}} \right.$                                              
  224                                                                                                      
  1.7446   47           .3286           .3289                                                              252
  1.7125   15           .3410           .3415                                                              060
  1.7025     7          .3450           .3449                                                              622
  1.6521   17           .3664           .3669                                                              404
  1.6415   32           .3711           .3715                                                              234

These values are based on the unit cell parameters: *a* = 12.194 A, *b* = 10.268 A, *c* = 7.856 A.

###### 

X-ray diffraction powder data for the compound *5BaO*·*2Nb*~2~*O*~5~ (*CuK*α radiation)

  *d*        *I*/*I*~0~   1/*d*^2^~obs~   1/*d*^2^~calc~[a](#tfn6-jresv65an4p337_a1b){ref-type="table-fn"}   Hexagonal *hkl*
  ---------- ------------ --------------- ------------------------------------------------------------------ -----------------
  4.61         5          0.0471          0.0469                                                             101
  3.827        9          .0683           .0685                                                              102
  3.093      100          .1045           .1045                                                              103
  2.897      100          .1192           .1192                                                              110
  2.540        8          .1550           .1549                                                              104
  2.453        7          .1663           .1661                                                              201
  2.358      12           .1799           .1800                                                              005
  2.308      25           .1877           .1877                                                              202
  2.1324     14           .2199           .2198                                                              105
  2.1143     100          .2237           .2237                                                              203
  1.9106       9          .2739           .2741                                                              204
  1.8298     49           .2987           .2990                                                              106
  1\. 7080   62           .3428           .3429                                                              213
  1.6726     33           .3575           .3575                                                              300
  1.5963       7          .3924           .3926                                                              107
  1.5468     21           .4180           .4181                                                              206
  1.4487     27           .4765           .4767                                                              220
  1.3977       8          .5119           .5117                                                              207
  1.3644     22           .5372           $\left\{ {\mspace{7mu}\begin{array}{l}                             216
                                          {.5373} \\                                                         
                                          {.5375} \\                                                         
                                          \end{array}} \right.$                                              
  305                                                                                                        
  1.3120     21           .5809           .5812                                                              313
  1.2583       3          .6316           .6316                                                              314
  1.1940     15           .7003           .7004                                                              403
  1.1933     14           .7022           .7025                                                              119
  1.1363       9          .7744           .7756                                                              316
  1.1050     10           .8189           .8195                                                              323
  1.0953     11           .8335           .8342                                                              410
  1.0925       9          .8378           .8393                                                              1·1·10
  1.0577       5          .8939           .8948                                                              406
  1.0311       5          .9405           .9408                                                              309

These values are based on the hexagonal unit cell parameters: *a*=5.794 A, *c*=11.784 A.

###### 

Experimental data for compositions in the binary system *BaO*--*Nb*~2~*O*~5~

  Composition[a](#tfn8-jresv65an4p337_a1b){ref-type="table-fn"}   Heat treatment[b](#tfn9-jresv65an4p337_a1b){ref-type="table-fn"}   Results                                                                                           
  --------------------------------------------------------------- ------------------------------------------------------------------ --------------------------------------------------------- --------------- ----------------------- ---------------------------------------------------------------------
                                                                                                                                                                                                                                       
  *mole %*                                                        *mole %*                                                           *°C*                                                      *hr*                                    
  71.43                                                           28.57                                                              1300                                                      16              No melting               5BaO·2Nb~2~O~5~.
  (5:2)                                                           1330                                                               0.167                                                     do                 Do.                  
                                                                                                                                     1450                                                      .5              do                         Do.
                                                                                                                                     1480                                                      .5              do                      
                                                                                                                                     1490                                                      17              do                      
                                                                                                                                     1520                                                      0.5             do                      
                                                                                                                                     1540                                                      .5              do                       5BaO·2Nb~2~O~5~.
                                                                                                                                     1545                                                        .333          Completely melted.      
                                                                                                                                     1550                                                        .333          do                      
                                                                                                                                     1560                                                      .5              do                      
                                                                                                                                     1580                                                        .333          do                      
                                                                                                                                     1600                                                        .167          do                      
                                                                                                                                     1650                                                      .5              do                       5BaO·2Nb~2~O~5~.
  66.67                                                           33.33                                                              [d](#tfn11-jresv65an4p337_a1b){ref-type="table-fn"}1100   60              No melting               5BaO·2Nb~2~O~3~+Or−BaO·Nb~2~O~5~.
                                                                                                                                     1300                                                      0.5             do                         Do.
                                                                                                                                     1300                                                      16              do                         Do.
                                                                                                                                     1320                                                      0.25            Just began to melt.     
                                                                                                                                     1325                                                      .25             Some melting.           
                                                                                                                                     1346                                                      .25             Partially melted.       
                                                                                                                                     1350                                                      1.0             do                       5BaO·2Nb~2~O~5~+Or−BaO·Nb~2~O~5~.
                                                                                                                                     1400                                                      0.5             Considerably melted.       Do.
                                                                                                                                     1425                                                      .25             do                         Do.
                                                                                                                                     1440                                                      .25             do                         Do.
                                                                                                                                     1455                                                      .25             do                         Do.
                                                                                                                                     1500                                                      .5              Completely melted.         Do.
  60                                                              40                                                                 1320                                                      0.25            Just began to melt.     
                                                                                                                                     1330                                                        .167          Considerably melted.    
                                                                                                                                     1350                                                      .25             Completely melted.      
                                                                                                                                     1400                                                      .25             do                      
  54.55                                                           45.45                                                              1320                                                      0.167           Just began to melt.     
                                                                                                                                     1400                                                      .25             Partially melted.        Or−BaO·Nb~2~O~5~+5BaO·2Nb~2~O~5~.
                                                                                                                                     1422                                                      .25             do                      
                                                                                                                                     1432                                                      .25             Completely melted.      
                                                                                                                                     1442                                                      .25             do                      
                                                                                                                                     1461                                                      .25             do                      
  50                                                              50                                                                 [d](#tfn11-jresv65an4p337_a1b){ref-type="table-fn"}900    136             No melting               5BaO·2Nb~2~O~5~+Or−BaO·Nb~2~O~5~·+H−BaO·Nb~2~O~5~+3BaO·5Nb~2~O~5~.
                                                                                                                                     1050                                                      64                                       Or−BaO·Nb~2~O~5~+H−BaO·Nb~2~O~5~·+5BaO·2Nb~2~O~5~+3BaO·5Nb~2~O~5~.
                                                                                                                                     1100                                                      64              do                       H−BaO·Nb~2~O~5~+Or−BaO·Nb~2~O~5~.
                                                                                                                                     [d](#tfn11-jresv65an4p337_a1b){ref-type="table-fn"}1200   1               do                       Or−BaO·Nb~2~O~5~.
                                                                                                                                     [d](#tfn11-jresv65an4p337_a1b){ref-type="table-fn"}1310   1               do                         Do.
                                                                                                                                     1450                                                      0.33            do                         Do.
                                                                                                                                     1460                                                      0.33            Completely melted.         Do.
  48                                                              52                                                                 1100                                                      64              No melting               H−BaO·Nb~2~O~5~+Or−BaO·Nb~2~O~5~+3BaO·5Nb~2~O5.
                                                                                                                                     1200                                                      64              do                       Or−BaO·Nb~2~O~5ss~+3BaO·5Nb~2~O~5~.
                                                                                                                                     1275                                                      1               do                       Or−BaO·Nb~2~O~5ss~+6BaO·7Nb~2~O~5~+3BaO·5Nb~2~O~5~.
                                                                                                                                     1310                                                      16              do                       Or−BaO·Nb~2~O~5ss~+3BaO·5Nb~2~O~5~ (trace).
                                                                                                                                     1325                                                      0.33            do                         Do.
                                                                                                                                     1350                                                      .33             Just began to melt.        Do.
  46.15                                                           53\. 85                                                            1278                                                      2               No melting               6BaO·7Nb~2~O~5~+Or−BaO·Nb~2~O~5ss~+3BaO·5Nb~2~O~5~.
  (6:7)                                                                                                                                                                                                                                
                                                                                                                                     1300                                                      160.5           do                       6BaO·7Nb~2~O~5~.
                                                                                                                                     1325                                                      23              do                       6BaO·7Nb~2~O~5~+Or−BaO·Nb~2~O~5ss~+3BaO.5Nb~2~O~5~.
  45.45                                                           54.55                                                              1278                                                      64              No melting               6BaO·7Nb~2~O~5~+3BaO·5Nb~2~O~5~.
                                                                                                                                     1300                                                      0.833           do                         Do.
                                                                                                                                     1300                                                      160.5           do                         Do.
  45                                                              55                                                                 1275                                                      0.583           No melting               6BaO·7Nb~2~O~5~+3BaO·5Nb~2~O~5~.
                                                                                                                                     1310                                                      1.0             Partially melted.        6BaO·7Nb~2~O~5~+Tet−ss.
                                                                                                                                     1337                                                      0.167           do                       Or−BaO·Nb~2~O~5~+Tet−ss.
                                                                                                                                     1426                                                      0.167           Considerably melted.    
                                                                                                                                     1445                                                      0.167           Completely melted.      
  40                                                              60                                                                 1277                                                      15              No melting               3BaO·5Nb~2~O~5~+6BaO·7Nb~2~O~5~.
                                                                                                                                     1290                                                      0.167           Just began to melt.     
                                                                                                                                     1292                                                      1.0             do                       Tet−ss+6BaO·7Nb~2~O~5~.
                                                                                                                                     1325                                                      0.167           Considerably melted.       Do.
                                                                                                                                     1335                                                        .167          do                       Tet−ss+or−BaO·Nb~2~O~5~.
                                                                                                                                     1353                                                        .167          do                         Do.
                                                                                                                                     1378                                                        .167          do                      
                                                                                                                                     1386                                                        .167          Completely melted.      
  38.46                                                           61.54                                                              1277                                                      15              No melting               3BaO·5Nb~2~O~5~+6BaO·7Nb~2~O~5~.
  37.5                                                            62.5                                                               1275                                                      0.583           No melting               3BaO·5Nb~2~O~5~.
  (3:5)                                                           1275                                                               1.0                                                       do                 Do.                  
                                                                                                                                     1291                                                      0.167           Just began to melt.     
                                                                                                                                     1296                                                        .167          Considerable melting.   
                                                                                                                                     1300                                                      .5              do                       Tet−ss+6BaO·7Nb~2~O~5~.
                                                                                                                                     1310                                                      .75             do                      
                                                                                                                                     1327                                                      1.0             do                      
                                                                                                                                     1330                                                      0.167           do                      
                                                                                                                                     1337                                                        .167          Completely melted.         Do.
  36                                                              64                                                                 1291                                                      0.167           Just began to melt.     
                                                                                                                                     1296                                                        .167          Considerably melted.    
                                                                                                                                     1301                                                      1.0             do                       Tet−ss+6BaO·7Nb~2~O~5~ (trace).
                                                                                                                                     1310                                                      0.167           do                      
  35                                                              65                                                                 1290                                                      0.167           Just began to melt.     
                                                                                                                                     1301                                                        .167          Completely melted.      
  33.33                                                           66.67                                                              1277                                                      .5              No melting              
                                                                                                                                     1285                                                        .167          do                      
                                                                                                                                     1292                                                        .333          do                       3BaO·5Nb~2~O~5~SS.
                                                                                                                                     1295                                                        .033          Just began to melt.     
                                                                                                                                     1300                                                      1.0             Partially melted.        3BaO·5Nb~2~O~5~SS (+Tet−ss?).
                                                                                                                                     1306                                                      0.167           Completely melted.      
                                                                                                                                     1310                                                        .083          do                      
                                                                                                                                     1352                                                      .25             do                      
                                                                                                                                     1400                                                        .167          do                       Tet−ss.
  28.57                                                           71.43                                                              1275                                                        .583          No melting               3BaO·5Nb~2~O~5~ss.
                                                                                                                                     1295                                                        .033          do                      
                                                                                                                                     1306                                                        .167          Partially melted.       
                                                                                                                                     1310                                                      .5              Completely melted.       Tet−ss.
  27                                                              73                                                                 1301                                                      16              No melting               BaO·3Nb~2~O~5~ss.
  25                                                              75                                                                 1292                                                      1.0             No melting              
  (1:3)                                                           1310                                                               0\. 333                                                   do               BaO·3Nb~2~O~5~.        
                                                                                                                                     1311                                                        .167          do                      
                                                                                                                                     1314                                                        .083          Partially melted.        BaO·3Nb~2~O~5~ (+Tet−ss?).
                                                                                                                                     1315                                                        .167          do                      
                                                                                                                                     1320                                                                      Completely melted.      
                                                                                                                                     1325                                                      .25             do                       Tet−ss.
                                                                                                                                     1350                                                        .083          do                         Do.
  24                                                              76                                                                 1300                                                        .167          No melting               BaO·3Nb~2~O~5~+Nb~2~O~5~ (trace).
                                                                                                                                     1305                                                        .167          do                      
                                                                                                                                     1315                                                        .167          Just began to melt.     
                                                                                                                                     1321                                                        .167          Partially melted.       
  20                                                              80                                                                 1314                                                        .167          No melting              
                                                                                                                                     1316                                                        .167          Just began to melt.     
                                                                                                                                     1323                                                        .167          Partially melted.       
                                                                                                                                     1327                                                        .167          do                      
                                                                                                                                     1394                                                        .167          Considerably melted.    
                                                                                                                                     1399                                                        .167          Completely melted.      
  15                                                              85                                                                 1316                                                        .167          No melting              
                                                                                                                                     1326                                                        .167          Just began to melt.     
                                                                                                                                     1438                                                        .167          Completely melted.      
  10                                                              90                                                                 1275                                                        .583          No melting               Nb~2~O~5~+BaO· 3Nb~2~O~5~.
                                                                                                                                     1310                                                      .75             do                         Do.
                                                                                                                                     1332                                                      .25             do                      
                                                                                                                                     1343                                                      .25             do                      
                                                                                                                                     1392                                                        .333          Just began to melt.     
                                                                                                                                     1415                                                        .167          Partially melted.       
                                                                                                                                     1448                                                      .25             Considerably melted.    
                                                                                                                                     1465                                                        .333          do                      
                                                                                                                                     1480                                                        .167          Completely melted.      
  5                                                               95                                                                 1439                                                        .167          Just began to melt.     
                                                                                                                                     1482                                                        .167          Completely melted.      
  0                                                               100                                                                1474                                                        .333          No melting              
                                                                                                                                     1483                                                      .5              do                      
                                                                                                                                     1490                                                        .167          Completely melted.      
                                                                                                                                     1502                                                        .167          do                      

See footnotes at end of table.

All specimens containing more than 71.43 mole percent BaO reacted with the Pt containers.

Unless otherwise indicated all specimens were quenched in sealed Pt tubes.

The phases identified are given in the order of the amount present at room temperature. The phases are not necessarily those present at the temperature to which the specimen was heated. H---hexagonal, Or---orthorhombic, Tet---tetragonal, ss---solid solution.

These specimens were heated in air on Pt foil, and slow cooled.