Structural features and thermal expansion of zinc
aluminosilicate quartz solid solutions

Alessio Zandonà, Beatriz Paiva da Fonseca, Gundula Helsch, Vinzent Olszok, Michael J Pitcher, Haytem Bazzaoui, Alfred Weber, Mathieu Allix, Joachim Deubener

<figure><img src="image_1.png" /></figure>

To cite this version:

Alessio Zandonà, Beatriz Paiva da Fonseca, Gundula Helsch, Vinzent Olszok, Michael J Pitcher, et al. Structural features and thermal expansion of zinc aluminosilicate quartz solid solutions. Journal of the European Ceramic Society, 2024, 44 (13), pp.7769-7777. 10.1016/j.jeurceramsoc.2024.05.046. hal-04728426

HAL Id: hal-04728426

https://hal.science/hal-04728426v1

Submitted on 14 Oct 2024

**HAL** is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_2.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

# Structural features and thermal expansion of zinc aluminosilicate quartz solid solutions

Alessio Zandonà<sup>a,*</sup>, Beatriz Paiva Da Fonseca<sup>a</sup>, Gundula Helsch<sup>a</sup>, Vinzent Olszok<sup>b</sup>, Michael J. Pitcher<sup>c</sup>, Haytem Bazzaoui<sup>c</sup>, Alfred P. Weber<sup>b</sup>, Mathieu Allix<sup>c</sup>, Joachim Deubener<sup>a</sup>

<sup>a</sup> Clausthal University of Technology, Institute of Non-Metallic Materials, 38678 Clausthal-Zellerfeld, Germany

<sup>b</sup> Clausthal University of Technology, Institute of Particle Technology, 38678 Clausthal-Zellerfeld, Germany

<sup>c</sup> CNRS, CEMHTI UPR3079, Univ. Orléans, F-45071 Orléans, France

## Abstract

Zinc aluminosilicate (ZAS) glasses were synthesized along the peraluminous join ($SiO_2$ contents between 95 and 50 mol%) by melt-quenching or sol-gel spray-drying and subjected to controlled heat treatments to obtain ZAS quartz solid solutions ($Zn-Qz-ss$). The precipitation of $Zn-Qz-ss$ is non-stoichiometric with respect to their parent glass and the crystals undergo a compositional evolution during annealing, even in absence of secondary crystalline phases. Near-hexagonal high-quartz-like crystals with negative thermal expansion (down to $-3 \times 10^{-6} K^{-1}$) can be obtained in the range 50-80 mol% $SiO_2$, while $SiO_2$-richer crystals exhibit positive thermal expansion at room temperature (up to $29 \times 10^{-6} K^{-1}$). $Zn^{2+}$ ions occupy two distinct positions within the structural channels of quartz, with a strong preference for 4-fold coordination. In analogy to lithium aluminosilicate quartz solid solutions ($Li-Qz-ss$), the low-to-high phase transition exhibits a linear correlation to the composition of the crystals.

**Keywords:** X-ray diffraction, quartz solid solutions, quartz inversion, stuffed derivatives of $SiO_2$, negative thermal expansion

*Corresponding author: Alessio Zandonà, alessio.zandona@tu-clausthal.de
# 1. Introduction

Lithium aluminosilicate (LAS) glass-ceramics represent a state-of-the-art solution for the production of transparent monolithic zero-thermal-expansion materials [1,2]. Their applications range from thermal-shock-resistant cooktop panels and fire-viewing windows to high-precision optics and telescope mirror blanks. The advantageous thermal properties of these glass-ceramics arise from their content in stuffed derivatives of $SiO_2$ polymorphs [3] with low thermal expansion, such as keatite solid solution [4] or, more frequently, quartz solid solution (Qz-ss) crystals [5-7]. The latter crystals, though being frequently referred to in the literature just through their three main oxide components ($Li_2O$, $Al_2O_3$ and $SiO_2$) as lithium aluminosilicate Qz-ss (for brevity, termed Li-Qz-ss [8] in the following), represent in commercial materials a complex solid solution, which can be described through the generalized formula $Zn_xMgyLi_zAl_{(2x+2y+z)+u}P_uSi_{1-(2x+2y+z)-2u}O_2$. Their tectosilicate structure is built up by helical chains of tetrahedra: while $Al^{3+}$ and $P^{5+}$ can substitute $Si^{4+}$ in the tetrahedral framework sites, $Li^+$, $Mg^{2+}$ and $Zn^{2+}$ occupy otherwise vacant positions within open channels running parallel to the c direction [1]. More recently, the possibility of crystallizing Qz-ss over a much wider compositional landscape ($M_{0.5x}Al_xSi_{1-x}O_2$, with $M = Co^{2+}$, $Ni^{2+}$, $Fe^{2+}$ and/or $Mn^{2+}$) has been demonstrated [9,10].

Such chemical versatility is crucial for the functional role of Qz-ss in glass-ceramics obtained by controlled crystallization [11] of multicomponent parent glasses. The thermal expansion of Qz-ss can be tuned through compositional adjustments to obtain a slight thermal contraction, which yields then a thermally invariant behaviour of the overall material through the combination with a positively expanding residual amorphous phase [1]. Referring to the compositional endmembers with major technological relevance, Li-Qz-ss are those best characterized in the scientific literature, also due to the relative ease by which they can be crystallized from glass (they exhibit a thermodynamic stability field around the composition $Li_{0.5}Al_{0.5}Si_{0.5}O_2$ [12]). At room temperature, they exhibit trigonal symmetry (enantiomorphic space groups: $P3_121$ or $P3_221$, just like low or α-quartz) and positive thermal expansion in the compositional range 100-83 mol% $SiO_2$; at higher levels of substitution [$Si^{4+} \rightarrow Al^{3+} + Li^+$], they are hexagonal (enantiomorphic space groups: $P6_422$ or $P6_222$, as for high or β-quartz) and display zero thermal expansion or a slight thermal contraction [13-16]. On the contrary, magnesium aluminosilicate (MAS) Qz-ss (for brevity, termed Mg-Qz-ss [8] in the following) have been recently shown to exhibit trigonal symmetry
throughout their solid solution range (SiO₂–Mg₀.₂₅Al₀.₅Si₀.₅O₂), coupled with a positive thermal expansion [17–19].

Concerning zinc aluminosilicate (ZAS) Qz-ss (for brevity, termed Zn-Qz-ss [8] in the following), only limited information is available in the scientific literature: while early crystallographic investigations are fragmentary [20], Petzoldt [6] recorded lattice parameters and observed negative or zero thermal expansion (by dilatometry) in the approximate compositional range 50–70 mol% SiO₂. Müller et al. [21] confirmed negative thermal expansion along both c and a directions in a sample with nominal composition Zn₀.₁₆₅Al₀.₃₃Si₀.₆₇O₂. More recently [9], a Rietveld refinement of a Zn-Qz-ss with nominal stoichiometry Zn₀.₂₂Al₀.₄₄Si₀.₅₆O₂ revealed a structure that was very close to that of high quartz, associated with a noticeable negative thermal expansion. Zn ions were accommodated over two distinct sites within the framework channels, as already speculated by early authors [20].

This work aims at closing the existing gaps in the current crystallographic description of Zn-Qz-ss, with a particular focus on structure-property relationships linking symmetry, Zn²⁺ incorporation and thermal expansion behaviour. These results are meant to provide a sounder foundation for the technological enhancement of Qz-ss-based zero-thermal-expansion glass-ceramics, favouring smart material design over trial-and-error approaches.

86

## 2. Experimental

### 2.1 Glass synthesis

Most of the ZAS precursor glasses were synthesized by melt-quenching in a laboratory furnace (Tab. 1). Batches of 5 g were prepared by manually mixing SiO₂ (99.9%, Chempur), Al₂O₃ (99.999%, Strem Chemicals) and ZnO (99.999%, Strem Chemicals) in an agate mortar, with ethanol as a suspending agent. After drying, melting was performed at 1650 °C for 45 min, repeating the procedure twice to ensure chemical homogenization; the melts were quickly quenched into glasses by immersing the bottom of the Pt-Rh20 crucible in water. In the case of sample Z90m, the melting temperature was increased to 1700 °C due to the high melt viscosity. The glasses were manually grinded in an agate mortar, obtaining fine amorphous powders for the subsequent heat treatments.

99

Some compositions were additionally prepared by sol-gel spray-drying (Tab. 1), following the procedure optimized in previous works [10,16,22]. In contrast to the melt-
quenched samples, a ZnO excess (2.5% of the total SiO₂ molar content) was invariably introduced with respect to the nominal stoichiometry to foster the crystallization of Qz-ss, as similarly observed in Li- and Co-containing samples comprising a Li₂O excess [10,16,23]. Tetraethoxysilane (TEOS, 99.9%, Thermo Fisher) was hydrolyzed in a solution containing methanol (≥ 99.9%, VWR Chemicals), nitric acid (1 mol/L, ORG Chemical) and distilled water in stoichiometric proportions. To ensure homogeneity and full hydrolysis, the solution was mixed for 30 minutes using a magnetic stirrer. Zn(NO₃)₂·6H₂O (≥ 99.0%, Merck) (including the above-mentioned Zn excess) and Al(NO₃)₃·9H₂O (≥ 99.0%, Thermo Fisher) were separately dissolved in methanol in the desired ratio and then aggregated to the TEOS solution. The final solution was further diluted with methanol to achieve an appropriate viscosity and concentration for spray-drying. The spray-drying equipment consisted of a PALAS AGK 2000 atomizer (operated with 2.5 bar pressurized air), a tube furnace set at 400 °C and a heated particle filter holder. The mean residence time of the aerosol within the tube furnace was approximately 1.5 s.

<table><caption>Table 1. List of the samples synthesized within this work by melt-quenching or sol-gel spray-drying, with indication of the nominal glass stoichiometry as well as the targeted stoichiometry of Qz-ss according to the substitution [Si⁴⁺ ↔ Al³⁺ + 0.5 Zn²⁺].</caption><thead><tr><th rowspan="2">Sample</th><th rowspan="2">Synthesis route</th><th colspan="3">Nominal glass composition</th><th rowspan="2">Target Qz-ss stoichiometry</th></tr><tr><th>ZnO (mol%)</th><th>Al₂O₃ (mol%)</th><th>SiO₂ (mol%)</th></tr></thead><tbody><tr><td>Z50m</td><td>melt-quenching</td><td>25.0</td><td>25.0</td><td>50.0</td><td>Zn₀.25Al₀.5Si₀.5O₂</td></tr><tr><td>Z60m</td><td>melt-quenching</td><td>20.0</td><td>20.0</td><td>60.0</td><td>Zn₀.2Al₀.4Si₀.6O₂</td></tr><tr><td>Z70m</td><td>melt-quenching</td><td>15.0</td><td>15.0</td><td>70.0</td><td>Zn₀.15Al₀.3Si₀.7O₂</td></tr><tr><td>Z77m</td><td>melt-quenching</td><td>11.5</td><td>11.5</td><td>77.0</td><td>Zn₀.115Al₀.23Si₀.77O₂</td></tr><tr><td>Z80m</td><td>melt-quenching</td><td>10.0</td><td>10.0</td><td>80.0</td><td>Zn₀.1Al₀.2Si₀.8O₂</td></tr><tr><td>Z83m</td><td>melt-quenching</td><td>8.5</td><td>8.5</td><td>83.0</td><td>Zn₀.085Al₀.17Si₀.83O₂</td></tr><tr><td>Z85m</td><td>melt-quenching</td><td>7.5</td><td>7.5</td><td>85.0</td><td>Zn₀.075Al₀.15Si₀.85O₂</td></tr><tr><td>Z87m</td><td>melt-quenching</td><td>6.5</td><td>6.5</td><td>87.0</td><td>Zn₀.065Al₀.13Si₀.87O₂</td></tr><tr><td>Z90m</td><td>melt-quenching</td><td>5.0</td><td>5.0</td><td>90.0</td><td>Zn₀.05Al₀.1Si₀.9O₂</td></tr><tr><td>Z66s</td><td>sol-gel with ZnO excess</td><td>18.0</td><td>16.4</td><td>65.6</td><td>Zn₀.165Al₀.33Si₀.67O₂ (67 mol% SiO₂)</td></tr><tr><td>Z80s</td><td>sol-gel with ZnO excess</td><td>11.8</td><td>9.8</td><td>78.4</td><td>Zn₀.1Al₀.2Si₀.8O₂ (80 mol% SiO₂)</td></tr><tr><td>Z90s</td><td>sol-gel with ZnO excess</td><td>7.1</td><td>4.9</td><td>88.0</td><td>Zn₀.05Al₀.1Si₀.9O₂ (90 mol% SiO₂)</td></tr></tbody></table>
<table><tr><td>Z95s</td><td>sol-gel<br>with ZnO excess</td><td>4.8</td><td>2.4</td><td>92.8</td><td>Zn<sub>0.025</sub>Al<sub>0.05</sub>Si<sub>0.95</sub>O<sub>2</sub><br>(95 mol% SiO<sub>2</sub>)</td></tr></table>

## 2.2 Crystallization heat treatments

Melt-quenched powders were all treated in an Anton Paar HTK1200N chamber mounted on a diffractometer. First, exploratory HT-XRD experiments were run to gain an overview of the crystallization sequence between 850 °C and 1150 °C (heating ramps at 30 K min⁻¹), with 15 min isothermal dwells every 50 °C to acquire X-ray diffraction (XRD) patterns. For Z90m, the maximum temperature was increased to 1200 °C. Moreover, several samples were crystallized isothermally for 1, 6 or 8 h at temperatures between 850 °C and 1100 °C using the same apparatus, to study in more detail the structural evolution of Qz-ss.

Based on such preliminary experiments, several additional heating schedules were attempted for each composition to maximize Qz-ss content (and its crystallinity) and minimize the formation of secondary phases. They followed two main strategies: (i) repeating the same exploratory HT-XRD experiments detailed above between 850 °C and 1150 °C, stopping at an intermediate annealing stage identified as optimal because of a high crystalline content and no formation of secondary phases; (ii) an initial ramp at a rate of 30 K min⁻¹ up to a comparatively low target temperature, followed by an isothermal dwell of 6 h.

As for the spray-dried powders, they were pre-emptively treated at 600 °C for 30 min in a laboratory furnace to ensure complete decomposition of the organic precursors and solvent removal. They were then heated in the same laboratory furnace at a rate of 10 K min⁻¹ to various temperatures between 800 °C and 1050 °C, with an isothermal dwell of 30 min. After XRD characterization, the best samples (with the lowest content of residual glass and secondary phases) obtained from such treatments were selected for further crystallographic investigation. In the case of sample Z95s, the best heat treatment was instead identified with a similar approach as for melt-quenched samples, relying on HT-XRD experiments. A list of the selected samples is provided in Tab. 2.

## 2.3 Powder diffraction

Laboratory powder XRD data were acquired in Bragg-Brentano geometry using Cu Kα radiation, either on a Bruker D8 Advance diffractometer equipped with a
LynxEye XE line detector or on a Malvern Panalytical Empyrean diffractometer mounting a PIXcel 1D detector. In both cases, an Anton Paar HTK1200N heating chamber was available for performing in-situ high-temperature experiments, including measurements of thermal expansion and low-to-high phase transition up to 600 °C. Temperature calibration was performed as described previously [24]. It is worth mentioning that the chamber used for the explorative experiments between 850 °C and 1150 °C (shown in Fig. 1) was devoid of automatic sample position adjustment system. Some melt-quenched samples (Z60m, Z70m, Z77m, Z80m, Z83m and Z85m) were additionally characterized in Debye-Scherrer geometry using synchrotron radiation (calibrated wavelength: 0.67153 Å) at the beamline CRISTAL of the SOLEIL synchrotron in Saint Aubin, Essonne (France), mounting a Dectris Mythen line detector. Samples were loaded in Kapton capillaries for room temperature experiments and in SiO₂ capillaries for high-temperature ones, which were conducted up to 600 °C using a calibrated hot-air blower.

Data evaluation involved Pawley and Rietveld refinements that were performed using the software HighScore Plus (Panalytical). To take into account the occasionally poor quality of the crystallized samples, the uncertainty of the determined values was set as five times the estimated standard deviations provided by the software. Structural plots were produced using the software VESTA [25].

# 3. Results

## 3.1 Crystallization sequence

The samples were initially subjected to HT-XRD measurements up to 1150 °C, to gain an overview of the crystallization sequence. As known from literature [6,26], ZAS glasses exhibit virtually no volume nucleation in the absence of seed formers, so that the samples were invariably crystallized in powdered form. Zn-Qz-ss was the first phase detected in all samples (see for instance Fig. 1A), but the evolution of the crystalline content differed as a function of glass composition. A qualitative evaluation of the results (Fig. 1B) reveals that only samples between 50 and 80 mol% SiO₂ content can yield high fractions of Zn-Qz-ss with a negligible amount of residual amorphous phase. In such samples, heating to excessively high temperatures invariably brought about a decomposition of the formed Zn-Qz-ss, whose peaks underwent broadening and splitting and shifted to higher 2θ angles, with the concurrent precipitation of gahnite, that is ZnAl₂O₄ spinel (starting from 1100 °C in Fig. 1A). Interestingly, the
temperature threshold for the formation of gahnite shifted to higher temperatures with an increasing SiO₂ content of the starting glass, possibly in correlation with an increasing viscosity of the crystallizing melt. The high angle peak shift observed for Zn-Qz-ss crystals is consistent with a SiO₂ enrichment of the crystals due to partial structural unstuffing leading to a contraction of the unit cell. Such metastability leading to spinel formation was similarly observed in the past in Mg-Qz-ss [6,19,27], whose unstuffing behaviour during heating was intensely investigated as a possible synthesis route for high-strength glass-ceramics [28–31]. Samples with a SiO₂ content higher than 80 mol% invariably retained high amounts of residual amorphous phase even up to 1200 °C; at temperatures exceeding 1150 °C, the concomitant appearance of gahnite and cristobalite was detected.

<figure><img src="image_3.png" /><figcaption>Figure 1. (A) HT-XRD results for sample Z70m, measured during heating from 850 °C to 1150 °C (intensity in logarithmic scale). (B) Qualitative summary of the phase assemblages observed during HT-XRD measurements of samples synthesized by melt-quenching. Labels: G for glass, Q for Zn-Qz-ss, S for gahnite, C for cristobalite.</figcaption></figure>

Based on the above-described measurements, suitable temperatures were selected for each melt-quenched composition in order to investigate the formation of Zn-Qz-ss by HT-XRD isothermally and in more detail. All samples exhibited a gradual increase in Zn-Qz-ss content with time (see for instance Fig. 2A). Although no secondary phases were detected during these measurements apart from a residual amorphous fraction, Zn-Qz-ss displayed also here a time-dependent peak shift towards higher 2θ values during their formation in samples with a SiO₂ content equal
to or higher than 60 mol% (an example in Fig. 2A). In other words, despite the absence of a secondary gahnite phase, Zn-Qz-ss crystals underwent a gradual SiO₂ enrichment during their direct precipitation from glass. The peaks did not perceivably broaden during the process, suggesting an overall compositional evolution rather than the successive precipitation of gradually SiO₂-richer crystals. The unit cell volumes extracted by Pawley refinements exhibit a near-linear correlation to the total amount of crystallized Zn-Qz-ss (estimated through the integrated intensity of the (011) peak), as previously observed in glass-ceramics [32] but never reported in glasses devoid of nucleating agents. It is worth mentioning that this behaviour was absent in Li-Qz-ss crystallized from ternary LAS glasses, investigated in previous works [15,23] (see also Fig. S1 of the Supplementary Materials). Nevertheless, ZAS samples with a higher SiO₂ content expectedly and consistently show lower unit cell volumes than Zn- and Al-richer samples, reaffirming the key role of the starting glass composition in determining the stoichiometry (and therefore the properties, see also below) of Zn-Qz-ss crystals. Considering the sluggish kinetics of crystallization showed during these isothermal treatments (for instance, comparing the integrated peak intensities of Z90m and Z80m after one hour in Fig. 2B), the results additionally confirmed that it would be impossible to crystallize high fractions of Zn-Qz-ss in samples with a SiO₂ content higher than 80 mol%.

<figure><img src="image_4.png" /><figcaption>Figure 2. (A) HT-XRD results obtained from sample Z80m during an isothermal dwell of 1 h at 950 °C (6 consecutive measurements, each lasting 10 min). All identifiable peaks can be assigned to Qz-ss and exhibit a time-dependent shift to higher 2θ</figcaption></figure>
angles. (B) Unit cell volumes of Zn-Qz-ss determined by Pawley refinements of HT-XRD data collected isothermally from various melt-quenched samples, plotted against the respective integrated intensity of the Qz-ss (011) peak. The left-most data points represent the first measurement of the isothermal dwell (elapsed time: 10 min), while the right-most data points correspond to last measurement (total durations: 1, 6 or 8 h). All samples are devoid of gahnite; Zn-Qz-ss is the only detectable phase in all samples.

Spray-dried sol-gel powders were subjected to several heat treatments in a laboratory furnace and measured ex situ (Fig. 3). The samples crystallized at noticeably lower temperatures than the melt-quenched glasses: for instance, it was possible to obtain Zn-Qz-ss already at 900 °C in Z80s, while Z80m started to crystallize at 950 °C (Fig. 1B). This may be attributed to the high surface-to-volume ratio of spray-dried powders [16] or to their residual volatile content [10], but above all to the introduced excess of ZnO that lowered melt viscosity and accelerated crystallization kinetics, as previously shown for a Li₂O excess [23]. A peak shift towards higher 2θ values (i.e., a gradual SiO₂ enrichment of the crystals) during crystallization and without the formation of secondary phases was evident also in this case (compare for example the XRD patterns obtained after annealing Z80s at 900 °C and 950 °C in Fig. 3A). The sol-gel route successfully yielded Zn-Qz-ss for all compositions, although the concurrent formation of cristobalite was unavoidable in the sample with 95 mol% SiO₂ (Fig. 3B), as similarly noticed above for SiO₂-rich melt-quenched glasses.

<figure><img src="image_5.png" /><figcaption>Figure 3. (A) XRD measurements of sample Z80s after heat treatments performed in a laboratory furnace between 850 °C and 1000 °C. (B) HT-XRD results acquired from</figcaption></figure>
sample Z95s during an isothermal hold at 1075 °C for 70 minutes. Labels: Q for Zn-Qz-ss, S for gahnite, C for cristobalite.

## 3.2 Crystallographic characterization

The preliminary data shown above revealed the need to carefully optimize the heat treatment conditions in order to perform a meaningful investigation of the structure-property relationship of Zn-Qz-ss as a function of crystal stoichiometry. As exemplified in detail for Z80s (Fig. S2 and Tab. S1), annealing conditions deeply affected indeed the crystalline assemblage of the samples, as well as the crystallographic features and thermal expansion behaviour of the obtained Zn-Qz-ss, due to the non-stoichiometric glass crystallization behaviour detailed above and, at higher temperatures, the decomposition of Zn-Qz-ss with the formation of gahnite. Each sample was therefore subjected to several heat treatments, eventually pinpointing optimal conditions yielding well-crystallized Zn-Qz-ss with as low as possible contents of residual glass and secondary phases such as gahnite and cristobalite. As shown below, this approach was found to provide the best correlation between crystallographic analysis and nominal crystal stoichiometry (Tab. 1).

Samples Z87m and Z90m were excluded from further treatment, since Zn-Qz-ss exhibited very broad peaks and were invariably accompanied by high fractions of secondary phases. The final selection of crystallized samples is summarized in Tab. 2, while XRD measurements are provided as Fig. S3 of the Supplementary Materials (laboratory XRD for Z50m, Z66s, Z80s, Z90s, Z95s and synchrotron XRD for Z60m, Z70m, Z77m, Z80m, Z83m and Z85m). Excluding sample Z95s that contained relatively high amounts of cristobalite, all the above-selected glasses could be crystallized into Zn-Qz-ss with none or only minor contents of secondary phases. The amorphous fraction of the powders was also generally low, but grew as a function of the SiO₂ content due to their increasingly low tendency towards crystallization. Zn-Qz-ss invariably exhibited non-negligible peak width and asymmetry, most likely arising from a compositional distribution of the crystals formed in each sample (as corroborated by the peak shifts observed during crystallization, described in Section 3.1). Various data analysis approaches were attempted to describe this peak shape during Pawley and Rietveld refinements, involving symmetric (Figs. S4-S7 and Tabs. S2 and S3 of the Supplementary Materials) or asymmetric peak shape functions and the possible simultaneous refinement of several Qz-ss phases with slightly different
lattice parameters (Fig. S8, Tabs. S6 and S7), as recently demonstrated for a stuffed derivative of cristobalite [33]. Since the different approaches delivered equivalent results in terms of average lattice parameters, data refinements discussed in the following were performed for simplicity using a single Zn-Qz-ss phase and symmetric peak shapes.

<table><caption>Table 2. Lattice parameters and coefficients of thermal expansion (CTEs) obtained by Pawley refinements of XRD data collected within this work from Zn-Qz-ss crystallized from glass powders. Numbers in parentheses provide the estimated uncertainty of the last digit.</caption><thead><tr><th>Sample</th><th>Heat treatment</th><th>a (Å)</th><th>c (Å)</th><th>Unit cell volume (Å³)</th><th>CTE 30-300 °C (10⁻⁶ K⁻¹)</th><th>CTE 30-600 °C (10⁻⁶ K⁻¹)</th></tr></thead><tbody><tr><td>Z50m</td><td>850 °C, 6 h</td><td>5.3068(7)</td><td>5.459(1)</td><td>133.15(3)</td><td>-3.0(1)</td><td>-2.9(1)</td></tr><tr><td>Z60m</td><td>875 °C, 6 h</td><td>5.2605(1)</td><td>5.4506(1)</td><td>130.63(1)</td><td>-2.4(1)</td><td>-2.2(1)</td></tr><tr><td>Z70m</td><td>1050 °C, 15 min</td><td>5.1922(2)</td><td>5.4493(2)</td><td>127.22(1)</td><td>-1.6(1)</td><td>-1.6(1)</td></tr><tr><td>Z77m</td><td>950 °C, 6 h</td><td>5.1530(3)</td><td>5.4431(3)</td><td>125.17(1)</td><td>-0.5(1)</td><td>-1.0(1)</td></tr><tr><td>Z80m</td><td>950 °C, 6 h</td><td>5.1491(4)</td><td>5.4458(4)</td><td>125.04(1)</td><td>-0.1(1)</td><td>-0.8(1)</td></tr><tr><td>Z83m</td><td>1000 °C, 6 h</td><td>5.1056(2)</td><td>5.4484(3)</td><td>123.00(1)</td><td>4.5(1)</td><td>1.4(1)</td></tr><tr><td>Z85m</td><td>1050 °C, 6 h</td><td>5.0792(5)</td><td>5.4491(4)</td><td>121.74(2)</td><td>13.3(1)</td><td>5.6(1)</td></tr><tr><td>Z66s</td><td>850 °C, 30 min</td><td>5.2556(5)</td><td>5.463(3)</td><td>130.69(6)</td><td>-2.6(1)</td><td>-2.1(1)</td></tr><tr><td>Z80s</td><td>950 °C, 30 min</td><td>5.1327(6)</td><td>5.466(3)</td><td>124.70(6)</td><td>0.4(1)</td><td>-0.5(1)</td></tr><tr><td>Z90s</td><td>1050 °C, 30 min</td><td>5.0092(4)</td><td>5.444(2)</td><td>118.29(4)</td><td>29.4(1)</td><td>15.1(1)</td></tr><tr><td>Z95s</td><td>1075 °C, 30 min</td><td>4.9677(5)</td><td>5.429(3)</td><td>116.02(5)</td><td>21.5(1)</td><td>20.2(1)</td></tr></tbody></table>

The lattice parameters *a* and *c* obtained for Zn-Qz-ss agree well with the available literature references [9,21,34] and exhibit an evident correlation to the nominal composition of the starting glasses (Tab. 1 and Fig. 4A). Both lattice parameters increase with increasing stuffing degree of the Zn-Qz-ss crystals with respect to pure SiO₂ quartz, although the absolute variation is far lower for *c* than for *a* (~0.06 Å against ~0.4 Å, respectively). A broader comparison to Li-Qz-ss and Mg-Qz-ss is provided in Fig. 4B: analysing the mutual evolution of *a* and *c*, it is clear that Zn-Qz-ss display a similar behaviour to Li-stuffed Qz-ss, anticipating a certain structural affinity (see also below). The figure reports also literature values for Qz-ss crystallized in glass-ceramics: although the early seminal work by Petzoldt [6] probably suffered
from low accuracy of the instrumental capabilities of that time, a more recent study [35]
exhibits excellent agreement with the samples synthesized within this work.

<figure><img src="image_6.png" /></figure>

Figure 4. (A) Lattice parameters of Zn-Qz-ss synthesized within this work, in comparison to relevant literature sources for Zn-Qz-ss obtained from stoichiometric glasses (1: [34], 2: [9], 3: [21], pure quartz: [36]). (B) Correlation between *a* and *c* parameters of the Zn-Qz-ss crystallized within this work, in comparison to literature sources for Zn-Qz-ss (stoichiometric glasses: 1 [34], 2 [9], 3 [21]; glasses containing nucleating agents: 4 [6] and 5 [35]), Li-Qz-ss [9,14–16,37–39], Mg-Qz-ss [17,19] and pure quartz [36]. Arrows define the general direction of *a* and *c* evolution caused by an increasing stuffing degree of Qz-ss crystals. Estimated uncertainties are smaller than the depicted symbols.

Samples measured by synchrotron XRD and exhibiting a comparatively high crystalline quality (Z60m, Z70m, Z77m, Z80m) were additionally subjected to Rietveld refinements (Figs. S4-S7), using as starting point the structure previously determined for a Zn-Qz-ss with nominal stoichiometry Zn<sub>0.22</sub>Al<sub>0.44</sub>Si<sub>0.56</sub>O<sub>2</sub> [9]. The results (Tabs. S2 and S3) are in good agreement with this reference and yield overall crystal compositions (Fig. 5) that are close to the nominal target stoichiometry (Tab. 1). Despite the choice of a trigonal structural model (space group *P*3<sub>2</sub>21 as in low quartz), the refined average structures are very close to full hexagonality, with intertetrahedral rotation angles [40] ranging between 3.2(1)° and 5.1(1)°. It is worth mentioning that such angle is ~16° in (trigonal) pure quartz at room temperature and gradually decreases to ~7.5° during heating up to 571 °C; the phase transition occurring at 573 °C finally brings about a jump to 0°, which is the characteristic value for (hexagonal)
high quartz [41]. As already noted previously [9,20], Zn²⁺ ions occupy two different positions within the structural channels of the quartz framework, with a pronounced preference for the distorted tetrahedral site Zn1 over the distorted octahedral site Zn2 (Fig. 5). Therefore, the structure of Zn-Qz-ss appears very close to that of LAS crystals (fully hexagonal, with Li⁺ ions in 4-fold coordination [14]).

<figure><img src="image_7.png" /><figcaption>Figure 5. (A) Site occupation factors (sof) obtained by Rietveld refinements performed on crystallized samples Z60m, Z70m, Z77m and Z80m; the value at 55 mol% was obtained from a sample measured in a previous work [9]. (B) Refined Zn-Qz-ss structure for sample Z70m: side view of the pseudo-hexagonal channels defined by helical chains of tetrahedra (Al/Si in black, oxygens in blue), highlighting the two non-equivalent Zn sites (Zn1: distorted 4-fold coordination; Zn2: distorted 6-fold coordination; green spherical wedges detail the partial occupation of each position). (C) Refined Zn-Qz-ss structure for sample Z70m, viewed along the c direction.</figcaption></figure>

HT-XRD measurements were performed to investigate the thermal expansion behaviour of all samples up to 600 °C; the lattice parameters derived by Pawley refinements (Tabs. S4 and S5) enabled to compute the relative length changes Δl/l plotted in Fig. 6A. While most of the samples exhibit negative thermal expansion, samples with a SiO₂ content higher than 80 mol% clearly manifest a relatively abrupt transition between a positive expansion in the vicinity of room temperature and a negative one at higher temperatures. The resulting coefficients of thermal expansion
(CTEs; Tab.1 and Fig. 6B) show a gradual increase from negative values (ca. -3 × 10⁻⁶ K⁻¹ for Z50m) to highly positive ones (>20 × 10⁻⁶ K⁻¹ for Z95s) as the stuffing degree of the crystals decreases. The crossover occurs approximately at the composition of Z80m, whose CTE is very close to zero. CTEs computed for the temperature range 30-600 °C show a monotonous increase, whereas a maximum is identifiable at 90 mol% for the CTEs in the range 30-300 °C. This difference is evidently caused by the above-mentioned phase transition occurring above room temperature and shifting as a function of the sample composition. Overall, the agreement between literature sources [9,36], melt-quenched and sol-gel samples was excellent.

<figure><img src="image_8.png" /><figcaption>Figure 6. (A) Thermal expansion curves recorded by HT-XRD for Zn-Qz-ss synthesized within this work by melt-quenching and sol-gel. (B) Coefficients of thermal expansion (CTEs) obtained in the ranges 25-300 °C and 25-600 °C for the Zn-Qz-ss synthesized within this work, in comparison to relevant literature sources [9,36]. Estimated uncertainties are smaller than the depicted symbols.</figcaption></figure>

Finally, phase transition temperatures were extracted from the thermal expansion curves, as the intersection point of two tangents applied to the high-temperature (negative thermal expansion) and low-temperature (positive thermal expansion) intervals, respectively. As evident from Fig. 7, the obtained values exhibit a linear correlation to the nominal composition of the precursor glasses, with a good agreement between sol-gel and melt-quenched samples. The interpolated line separating the stability fields of high- and low-quartz-like phases is shifted to slightly lower SiO₂ contents with respect to the one previously determined for Li-Qz-ss [13,15,24]. Indeed, the composition marking the threshold for stabilizing high-quartz-
Isothermal HT-XRD measurements manifested that the formation of Zn-Qz-ss is a markedly non-stoichiometric process with respect to the composition of the precursor glass, even without the concurrent formation of secondary crystalline phases such as gahnite. Differences by more than 3% were identifiable between the unit cell volume of the first detectable Zn-Qz-ss and that of the final highly crystalline sample (Fig. 2), which account to a shift in SiO₂ content by 10 mol% or more. Highly crystalline samples exhibit however a very good correlation between lattice parameters and nominal composition (Fig. 4A), strongly suggesting that the final Zn-Qz-ss should closely correspond to the target stoichiometry. As such, crystals appear to be substantially enriched in Zn and Al at the moment of nucleation and to slowly converge towards the bulk composition of the glass upon further annealing. Such phenomenon was previously observed in glass-ceramics containing seed formers and attributed to crystal growth taking place through a heterogeneous glass, as chemical gradients could be identified by TEM around seed forming crystals [32]. Here, it may be explained through the existence of nanoscale compositional heterogeneities in the studied glasses, either already in the as-quenched state or as a consequence of secondary heat treatments.

Indeed, a stable liquid-liquid immiscibility field exists in the binary system ZnO-SiO₂ and on the ZnO-rich side of the ternary ZAS system, in the approximate range 60-95 mol% SiO₂ [42,43]. Although experimental proofs of phase separation occurring subsolidus along the peraluminous join of the ZAS system are lacking (due to the experimental challenges of observing phase separation in undercooled melts before the onset of crystallization), the above-mentioned superliquidus immiscibility dome may be extrapolated towards the centre of the ternary system at subsolidus (metastable) conditions [44,45]. The subsolidus thermodynamically stable phase assemblage for the analysed ZAS samples is invariably ZnAl₂O₄ (gahnite) + SiO₂ (quartz or cristobalite, depending on the temperature), which can be reached from the (virtually) homogeneous ZAS starting glass only through the onset of long-range diffusion already in the amorphous state. In other words, a strong thermodynamic driving force towards diffusive clustering of Zn and Al must exist at subsolidus conditions in the centre of the ZAS system.

An alternative pathway for lowering the internal energy of the system involves instead the (intermediate) formation of metastable Qz-ss crystals: in such case, the starting homogeneous ZAS glass would undergo diffusionless (stoichiometric)
442

structural ordering into Qz-ss. Nevertheless, our results suggest that diffusion-driven
chemical clustering and stoichiometric Qz-ss nucleation and growth compete and
widely overlap in terms of temperature and time, so that direct crystallization of Qz-ss
in the pristine aluminosilicate melt (i.e., before the onset of chemical diffusion) is
challenging or impossible. This interpretation actually achieves to explain also the
above-noted differences between the precipitation of Qz-ss in ZAS and LAS glasses:
in the latter system, the thermodynamically stable phase assemblages invariably
consist of lithium aluminosilicates [12] (Qz-ss or keatite solid solution), so that the
crystals can form stoichiometrically from the parent glass without a driving force
towards Li-Al clustering.

443

444

445

446

447

448

449

450

451

452

According to the picture sketched above, the ZAS melt/glass would start above
$T_g$ to separate through chemical diffusion into SiO₂-enriched and SiO₂-depleted
regions, with the latter consistently crystallizing first due to expectedly lower local
viscosity (viscosity decreases in the ZAS system both by SiO₂ depletion and ZnO
enrichment [46]), facilitating diffusionless structural ordering. Further crystal growth of
the so-formed Qz-ss through the SiO₂-richer regions would then bring about the
chemical re-equilibration (gradual peak shift) observed in Fig. 2. Concerning SiO₂-poor
samples that exhibited a lower extent of isothermal peak shifts (Z60m) or time-invariant
unit cell volumes (Z50m) during Qz-ss crystallization, they likely possessed a lower
thermodynamic driving force towards Zn and Al clustering, so that stoichiometric
structural ordering (i.e., Qz-ss crystallization) could kinetically prevail over chemical
diffusion and amorphous phase separation.

453

454

455

456

457

458

459

460

461

462

463

464

465

466

467

468

469

470

471

472

473

474

475

In this regards, more pervasive structural rearrangements are expected to be
necessary for the formation of Qz-ss in ZAS glasses with respect to LAS materials,
since Zn was reported to partially act as network-forming cation in 4-fold and 5-fold
coordination, with the non-negligible concurrent presence of high-coordinated Al[V] and
Al[VI] species [42]. Conversely, LAS glasses contain almost exclusively Al[IV] with Li⁺
ions providing charge compensation [47,48]. This difference may explain why Li-Qz-ss
invariably precipitate with a constant Al/Si ratio in LAS glasses (Fig. S1), while the
formation of ZAS crystals must be anticipated by structural and/or chemical
modifications of the precursor glasses. In addition, it is possible that the consistently
higher c values obtained for Qz-ss in sol-gel samples containing a ZnO excess (light
green circles in Fig. 4) may arise from a small fraction of Zn²⁺ still occupying framework
tetrahedral positions (as in the precursor glass), according to the substitution [Si⁴⁺_tetr
$\leftrightarrow$ Zn$^{2+}_{tetr} + Zn^{2+}_{channel}$]. Indeed, the ionic radius of Zn$^{2+}$ in tetrahedral coordination is noticeably higher than that of Si$^{4+}$ (0.60 against 0.26 Å [49], respectively). The data collected within this work, however, do not possess the necessary quality and resolution to test this speculation.

According to the performed crystallographic analyses, Zn-Qz-ss show strong similarities to LAS crystals, embodied by the strong preference of Zn$^{2+}$ ions for 4-fold coordination and by the high degree of hexagonality. As noticed above, the intertetrahedral rotation angles (Tab. S3) computed after Grimm and Dorner [40] are far lower than the value exhibited by low quartz at room temperature and actually correspond to values approached by pure quartz in the vicinity of (or even during) its phase transition, in the range 571-573 °C [41]. Considering also the above-detailed impossibility to obtain well-crystallized Zn-Qz-ss, it is very likely that the slight "trigonality" of the average structures determined within this work (and in a previous investigation [9]) may simply represent an artefact, with the crystals being in fact fully hexagonal. The observed sharp change in behaviour of the measured thermal expansion curves is a further hint at a phase transition occurring in the materials, which would speak for a hexagonal polymorph forming at high temperatures (as in pure quartz) and stabilized at lower temperatures by chemical substitutions, as in the LAS system. Along the same line of thoughts, it is worth mentioning here that similar views could be applicable to the MAS system, in which Qz-ss display similarly low tendency to crystallize due to comparatively high viscosity and the occurrence of competing phases such as cordierite or spinel [27]. Although recent investigations of Mg-Qz-ss delivered trigonal structures [17–19] with relatively high intertetrahedral rotation angles (~8°, reached by pure quartz at ca. 550 °C [41]), the thermal expansion curves of these crystals exhibit also phase transitions that shift as a function of crystal composition [19], so that this system likely deserves further crystallographic investigation.

Focussing on the comparison between LAS and Zn-Qz-ss, the stabilization of high-quartz-like frameworks (and CTEs < 0) appears to be slightly more effective through Li$^+$ ions, since the phase boundary is shifted to lower SiO$_2$ contents for ZAS crystals (Fig. 7). This is possibly due to the fact that, for a given Al/Si ratio, electroneutrality is achieved with half as many stuffing ions as in the case of LAS crystals, bringing about a more localized charge balancing and a less homogeneous "expansion" on the structural channels. However, it should not be disregarded that SiO$_2$-rich samples exhibiting a phase transition above room temperature contained a
510

511

512

513

514

515

non-negligible residual glass fraction (Fig. S3), so that Qz-ss crystals may be
significantly Zn- and Al-richer than the nominal glass composition. In this case, the data
points should be shifted to even lower SiO₂ contents, increasing the gap with respect
to the LAS system.

Conclusion

516

517

518

519

520

521

522

523

524

The results of this work provide a more accurate framework for the compositional design of Zn²⁺-stuffed Qz-ss that are obtainable in both melt-quenched and sol-gel glass-ceramics. The formation of Zn-Qz-ss from precursor glasses is shown to be non-stoichiometric and to be likely associated with immiscibility and/or a heterogeneous elemental distribution at the nanoscale. Nevertheless, high-quartz-like ZAS crystals exhibiting negative thermal expansion can be stabilized at SiO₂ contents lower than 80 mol%; at higher SiO₂ content, the thermal expansion of the crystals turns positive above room temperature and a low-to-high phase transition is identifiable, with a linear correlation to crystal stoichiometry as in the case of Li-Qz-ss.

525

526

Acknowledgement

527

528

529

530

531

532

533

534

The financial support of the Deutsche Forschungsgemeinschaft under the grant DE 598/37-1 is gratefully acknowledged. The authors acknowledge SOLEIL for provision of synchrotron radiation facilities and the block allocation group (BAG) RECIPROCS for the allocation of beamtime. They would like to thank Benoît Baptiste for his guidance during the application for beamtime, as well as Erik Elkaim for assistance while performing the measurements at the beamline Cristal. Funding was provided by the French National Research Agency (ANR) under project ANR-23-CE08-0013-01 HighFive.

535

536

References

537

538

[1] D. Krause, H. Bach, eds., Low Thermal expansion Glass Ceramics, Springer Berlin Heidelberg, 2005.

539

540

[2] G.H. Beall, Design and Properties of Glass-Ceramics, Annu. Rev. Mater. Sci. 22 (1992) 91–119. https://doi.org/10.1146/annurev.ms.22.080192.000515.

541

542

[3] M.J. Buerger, The stuffed derivatives of the silica structures, American Mineralogist 39 (1954) 600–614.

543

544

545

[4] W. Ostertag, G.R. Fischer, J.P. Williams, Thermal Expansion of Synthetic β-Spodumene and β-Spodumene—Silica Solid Solutions, Journal of the American Ceramic Society 51 (1968) 651–654. https://doi.org/10.1111/j.1151-2916.1968.tb12638.x.
546

547

548

[5] G.H. Beall, B.R. Karstetter, H.L. Rittler, Crystallization and Chemical Strengthening of Stuffed β-Quartz Glass-Ceramics, Journal of the American Ceramic Society 50 (1967) 181–190. https://doi.org/10.1111/j.1151-2916.1967.tb15077.x.

549

550

[6] J. Petzoldt, Metastabile Mischkristalle mit Quarzstruktur mit Oxidsystem Li2O-MgO-ZnO-Al2O3-SiO2, Glastechnische Berichte 40 (1967) 385–395.

551

552

[7] J. Petzoldt, Der Einbau von P2O5 in mestabile Mischkristalle mit Quarzstruktur des Grundsystems Li2O-MgO-ZnO-Al2O3-SiO2, Glastechnische Berichte 41 (1968) 181–189.

553

554

555

[8] J. Deubener, A. Zandonà, G. Helsch, Nomenclature of functional crystals in glass-ceramics: A recommendation based on aluminosilicate solid solutions, Journal of Non-Crystalline Solids 633 (2024) 122954. https://doi.org/10.1016/j.jnoncrysol.2024.122954.

556

557

558

559

[9] H. Bazzaoui, C. Genevois, E. Véron, M.J. Pitcher, M. Allix, A. Zandonà, Towards new zero-thermal-expansion materials: Li-free quartz solid solutions stuffed with transition metal cations, Journal of the European Ceramic Society 43 (2023) 1639–1648. https://doi.org/10.1016/j.jeurceramsoc.2022.11.035.

560

561

562

[10] B. Paiva Da Fonseca, A. Zandonà, G. Helsch, J. Deubener, Co2+-Stuffed Quartz Solid Solutions With Zero Thermal Expansion Synthesized by Sol-Gel Spray-Drying, Glass Eur 1 (2023) 25–36. https://doi.org/10.52825/glass-europe.v1i.460.

563

564

565

566

[11] J. Deubener, M. Allix, M.J. Davis, A. Duran, T. Höhe, T. Honma, T. Komatsu, S. Krüger, I. Mitra, R. Müller, S. Nakane, M.J. Pascual, J.W.P. Schmelzer, E.D. Zanotto, S. Zhou, Updated definition of glass-ceramics, Journal of Non-Crystalline Solids 501 (2018) 3–10. https://doi.org/10.1016/j.jnoncrysol.2018.01.033.

567

568

569

570

[12] R. Roy, D.M. Roy, E.F. Osborn, Compositional and Stability Relationships Among the Lithium Aluminosilicates: Eucryptite, Spodumene, and Petalite, Journal of the American Ceramic Society 33 (1950) 152–159. https://doi.org/10.1111/j.1151-2916.1950.tb12780.x.

571

572

573

574

[13] H. Xu, P.J. Heaney, A. Navrotsky, Thermal expansion and structural transformations of stuffed derivatives of quartz along the LiAlSiO4–SiO2 join: a variable-temperature powder synchrotron XRD study, Physics and Chemistry of Minerals 28 (2001) 302–312. https://doi.org/10.1007/s002690100165.

575

576

577

[14] H. Xu, P.J. Heaney, G.H. Beall, Phase transitions induced by solid solution in stuffed derivatives of quartz: A powder synchrotron XRD study of the LiAlSiO4-SiO2 join, American Mineralogist 85 (2000) 971–979. https://doi.org/10.2138/am-2000-0711.

578

579

580

[15] A. Zandona, G. Helsch, J. Deubener, Inversion of quartz solid solutions at cryogenic temperatures, Journal of the American Ceramic Society 103 (2020) 6630–6638. https://doi.org/10.1111/jace.17393.

581

582

583

584

[16] A. Zandona, G. Helsch, A. Martínez Arias, A.P. Weber, J. Deubener, Spray-dried sol-gel glass-ceramic powders based on the tunable thermal expansion of quartz and keatite solid solutions, Journal of the American Ceramic Society 105 (2022) 207–216. https://doi.org/10.1111/jace.18057.

585

586

587

[17] H. Xu, P.J. Heaney, P. Yu, H. Xu, Synthesis and structure of a stuffed derivative of α-quartz, Mg0.5AlSiO4, American Mineralogist 100 (2015) 2191–2198. https://doi.org/10.2138/am-2015-5303.

588

589

590

[18] H. Xu, X. Lü, P.J. Heaney, Y. Ren, Structural behavior of a stuffed derivative of α-quartz, Mg0.5AlSiO4, at high temperature: an in situ synchrotron XRD study, Physics and Chemistry of Minerals 46 (2019) 717–725. https://doi.org/10.1007/s00269-019-01033-1.

591

592

593

[19] A. Zandona, B. Rüdinger, J. Deubener, Mg-bearing quartz solid solutions as structural intermediates between low and high quartz, Journal of the American Ceramic Society 104 (2021) 1146–1155. https://doi.org/10.1111/jace.17517.
594
595

[20] M. Behruzi, Th. Hahn, Struktur und thermische ausdehnung des ungeordneten β-Eukryptits, Fortschr. Mineral. 55 (1977) 12–13.

596
597

[21] G. Müller, M. Hoffmann, R. Neeff, Hydrogen substitution in lithium-aluminosilicates, Journal of Materials Science 23 (1988) 1779–1785. https://doi.org/10.1007/BF01115722.

598
599
600

[22] A. Zandona, A. Martínez Arias, M. Gutbrod, G. Helsch, A.P. Weber, J. Deubener, Spray-Dried TiO2(B)-Containing Photocatalytic Glass-Ceramic Nanobeads, Advanced Functional Materials 31 (2021) 2007760. https://doi.org/10.1002/adfm.202007760.

601
602
603

[23] A. Zandona, G. Helsch, R. Al-Mukadam, J. Deubener, The effects of a Li2O excess on the crystallization sequence of lithium aluminosilicate glass powders, Journal of Non-Crystalline Solids 561 (2021) 120748. https://doi.org/10.1016/j.jnoncrysol.2021.120748.

604
605
606

[24] G. Helsch, J. Deubener, M. Rampf, M. Dittmer, C. Ritzberger, Crystallization and quartz inversion temperature of sol-gel derived LAS solid solutions, Journal of Non-Crystalline Solids 492 (2018) 130–139. https://doi.org/10.1016/j.jnoncrysol.2018.04.031.

607
608
609

[25] K. Momma, F. Izumi, VESTA: a three-dimensional visualization system for electronic and structural analysis, Journal of Applied Crystallography 41 (2008) 653–658. https://doi.org/10.1107/S0021889808012016.

610
611

[26] 若杉隆, 伊藤雅人, 岡田有史, 湯村尚史, 角野広平, ZnO-Al2O3-SiO2ガラスの結晶化機構, 材料 66 (2017) 389–392. https://doi.org/10.2472/jsms.66.389.

612
613
614

[27] W. Schreyer, J.F. Schairer, Metastable solid solutions with quartz-type structures on the join SiO2–MgAl2O4, Zeitschrift Für Kristallographie – Crystalline Materials 116 (1961) 60–82. https://doi.org/10.1524/zkri.1961.116.1-2.60.

615
616
617

[28] M. Dittmer, M. Müller, C. Rüssel, Self-organized nanocrystallinity in MgO–Al2O3–SiO2 glasses with ZrO2 as nucleating agent, Materials Chemistry and Physics 124 (2010) 1083–1088. https://doi.org/10.1016/j.matchemphys.2010.08.037.

618
619
620
621

[29] M. Dittmer, C.F. Yamamoto, C. Bocker, C. Rüssel, Crystallization and mechanical properties of MgO/Al2O3/SiO2/ZrO2 glass-ceramics with and without the addition of yttria, Solid State Sciences 13 (2011) 2146–2153. https://doi.org/10.1016/j.solidstatesciences.2011.09.005.

622
623
624
625

[30] M. Dittmer, C. Rüssel, Colorless and high strength MgO/Al2O3/SiO2 glass–ceramic dental material using zirconia as nucleating agent, Journal of Biomedical Materials Research Part B: Applied Biomaterials 100B (2012) 463–470. https://doi.org/10.1002/jbm.b.31972.

626
627
628

[31] P. Wange, T. Höhe, C. Rüssel, J. Dieter Schnapp, Microstructure-property relationship in high-strength MgO–Al2O3–SiO2–TiO2 glass-ceramics, Journal of Non-Crystalline Solids 298 (2002) 137–145. https://doi.org/10.1016/S0022-3093(02)00950-X.

629
630
631

[32] A. Zandona, C.B.M. Groß, B. Rüdinger, J. Deubener, A threshold heating rate for single-stage heat treatments in glass-ceramics containing seed formers, Journal of the American Ceramic Society 104 (2021) 4433–4444. https://doi.org/10.1111/jace.17822.

632
633
634
635

[33] A.J. Fernández-Carrión, A. Rakhmatullin, L. Yang, M.J. Pitcher, D. Massiot, F. Porcher, M. Allix, X. Kuang, Sodium Site Exchange and Migration in a Polar Stuffed-Cristobalite Framework Structure, Inorg. Chem. 60 (2021) 4322–4331. https://doi.org/10.1021/acs.inorgchem.1c00319.

636
637
638
639

[34] Roye et al., ICDD 00-032-1455, ICDD Grant-In-Aid (1981).

640
641

[35] E. Tkalcec, S. Kurajica, H. Ivankovic, Crystallization behavior and microstructure of powdered and bulk ZnO–Al2O3–SiO2 glass-ceramics, Journal of Non-Crystalline Solids 351 (2005) 149–157. https://doi.org/10.1016/j.jnoncrysol.2004.09.024.

[36] M.A. Carpenter, E.K.H. Salje, A. Graeme-Barber, B. Wruck, M.T. Dove, K.S. Knight, Calibration of excess thermodynamic properties and elastic constant variations
642

associated with the alpha <-->beta phase transition in quartz, American Mineralogist 83

643

(1998) 2-22. https://doi.org/10.2138/am-1998-1-201.

644

[37] C.-T. Li, The crystal structure of LiAlSi2O6 III (high-quartz solid solution), Zeitschrift

645

Für Kristallographie - Crystalline Materials 127 (1968) 327-348.

646

https://doi.org/doi:10.1524/zkri.1968.127.16.327.

647

[38] H.G.F. Winkler, Synthese und Kristallstruktur des Eukryptits, LiAlSiO4, Acta

648

Crystallographica 1 (1948) 27-34. https://doi.org/10.1107/S0365110X48000065.

649

[39] S. Ray, G.M. Muchow, High-Quartz Solid Solution Phases from Thermally Crystallized

650

Glasses of Compositions (Li2O,MgO).Al2O3.nSiO2, Journal of the American Ceramic

651

Society 51 (1968) 678-682. https://doi.org/10.1111/j.1151-2916.1968.tb15927.x.

652

[40] H. Grimm, B. Dorner, On the mechanism of the α-β phase transformation of quartz,

653

Journal of Physics and Chemistry of Solids 36 (1975) 407-413.

654

https://doi.org/10.1016/0022-3697(75)90066-9.

655

[41] S.M. Antao, Quartz: structural and thermodynamic analyses across the α ↔ β

656

transition with origin of negative thermal expansion (NTE) in β quartz and calcite, Acta

657

Crystallographica Section B 72 (2016) 249-262.

658

https://doi.org/10.1107/S205252061600233X.

659

[42] L. Cormier, L. Delbes, B. Baptiste, V. Montouillout, Vitrification, crystallization

660

behavior and structure of zinc aluminosilicate glasses, Journal of Non-Crystalline Solids

661

555 (2021) 120609. https://doi.org/10.1016/j.jnoncrysol.2020.120609.

662

[43] E.N. Bunting, PHASE EQUILIBRIA IN THE SYSTEM SiO2-ZnO1, Journal of the American

663

Ceramic Society 13 (1930) 5-10. https://doi.org/10.1111/j.1151-2916.1930.tb16797.x.

664

[44] F.Ya. Galakhov, V.I. Aver'yanov, V. Vavilonova, M.P. Areshev, Liquation in the systems

665

SrO (BaO)-Al2O3-SiO2, Fiz. Khim. Stekla 11 (1985) 712-716.

666

[45] B. Mysen, P. Richet, Chapter 8 - Properties of Aluminosilicate Systems, in: B. Mysen,

667

P. Richet (Eds.), Silicate Glasses and Melts (Second Edition), Elsevier, 2019: pp. 263-300.

668

https://doi.org/10.1016/B978-0-444-63708-6.00008-9.

669

[46] W.-Y. Kim, X. Yang, L. Yan, A.D. Pelton, S.A. Decterov, Modeling the viscosity of

670

silicate melts containing zinc oxide, Calphad 35 (2011) 542-550.

671

https://doi.org/10.1016/j.calphad.2011.09.005.

672

[47] P. Glatz, M. Comte, L. Cormier, L. Montagne, B. Doumert, G.G. Moore, Different roles

673

of phosphorus in the nucleation of lithium aluminosilicate glasses, Journal of Non-

674

Crystalline Solids 493 (2018) 48-56. https://doi.org/10.1016/j.jnoncrysol.2018.04.021.

675

[48] A. Ananthanarayanan, G.P. Kothiyal, L. Montagne, B. Revel, MAS-NMR studies of

676

lithium aluminum silicate (LAS) glasses and glass-ceramics having different Li2O/Al2O3

677

ratio, Journal of Solid State Chemistry 183 (2010) 120-127.

678

https://doi.org/10.1016/j.jssc.2009.10.006.

679

[49] R.D. Shannon, Revised effective ionic radii and systematic studies of interatomic

680

distances in halides and chalcogenides, Acta Crystallographica Section A 32 (1976) 751-

681

767. https://doi.org/10.1107/S0567739476001551.

682