We are IntechOpen,the world’s leading publisher ofOpen Access books
Built by scientists, for scientists

5,500

135,000

165M

Open access books available

International authors and editors

Downloads

Our authors are among the154

TOP 1%

12.2%

Countries delivered tomost cited scientists

Contributors from top 500 universities

Selection of our books indexed in the Book Citation Index
in Web of Science™ Core Collection (BKCI)Interested in publishing with us?
Contact book.department@intechopen.com
Numbers displayed above are based on latest data collected.
For more information visit www.intechopen.com

Chapter

Functional Materials Synthesis andPhysical Properties
Tatsuya Senzaki, Michiaki Matsukawa, Takanori Yonai,
Haruka Taniguchi, Akiyuki Matsushita, Takahiko Sasaki
and Mokoto Hagiwara

Abstract
A citrate pyrolysis technique is a unique route to prepare reactive precursor
mixtures through an ignition process of concentrated aqueous solution. This procedure enables to synthesize highly homogeneous and fine powders for functional
materials. The double-chain based superconductor Pr2 Ba4 Cu7 O15 δ and double
perovskite photocatalytic semiconductor Ba2 Tb(Bi,Sb)O6 were synthesized byusing the citrate pyrolysis technique. For the present sample with a reduction
treatment for 72 h, a sharp superconducting transition appeared at an onset temperature T c,on =26 K accompanied by a zero-resistance state at T c,zero =22 K. The
superconducting volume fraction estimated from the magnetization measurement
showed an excellent value of  58%. Both reduction treatment in a vacuum andsubsequent quenching procedure are needed to realize higher superconductivity
due to further oxygen defects. The polycrystalline samples for Ba2 Tb(Bi1 x ,Sbx )O6(x ¼ 0 and 0.5) were formed in the monoclinic and cubic crystal structures. We
conducted the gaseous 2-propanol (IPA) and methylene blue (MB) degradation
experiments under a visible light irradiation, to evaluate photocatalytic activities ofthe powder samples. For the Sb50% substituted sample, the highest performance of
MB degradation was observed. The effect of Sb-substitution on the photocatalytic
degradation of MB is in direct contrast to that on the IPA decomposition undervisible light irradiation. The enhanced photocatalytic properties in the citrate samples are attributed to their morphology, where fine particles are homogeneously
distributed with a submicron order.
Keywords: citrate pyrolysis technique, double-chain based superconductor,
pressure effect, double-perovskite oxide, photocatalytic semiconductor

1. Introduction
A citrate pyrolysis technique is similar to nitrate combustion synthesis methods[1] and a unique route to prepare reactive precursor mixtures through an ignition
process of concentrated aqueous solution including stoichiometric amounts of metal
ions. For 80 K-class high- T c cuprate superconductors such as YBa2 Cu4 O8 , highquality single-phase polycrystalline samples have been successfully prepared atambient oxygen pressure [2, 3]. We believe that the present technique is a powerfultool to fabricate highly homogeneous and fine crystalline grains for functional
materials, in comparison to conventional solid-state reaction methods.
1

Recent Perspectives in Pyrolysis ResearchHigh- T c copper-oxide superconductors discovered as far have close relationshipwith two-dimensional CuO2 planes. In quasi one-dimensional (1D) Cu2 O3 laddersystem without CuO2 planes, it has been reported in [4] that the application of
external pressure under 3 GPa causes bulk superconductivity at T c = 12 K. For
Pr-based copper oxides including insulating CuO2 planes, we have reported thatPr2 Ba4 Cu7 O15 δ (Pr247) with metallic CuO double-chain structure achieves asuperconducting-state with a higher T c (15 K) after a reduction treatment [5].
In the subsequent microscopic research on Pr247 [6], nuclear quadrupole resonance observations have resolved that the newly discovered superconductivity
occurs along the CuO double-chain block. The Pr-based cuprates, PrBa2 Cu3 O7 δ
(Pr123) and PrBa2 Cu4 O8 (Pr124), have identical crystal structures as Y-based highT c superconductors, YBa2 Cu3 O7 δ (Y123) and YBa2 Cu4 O8 (Y124), respectively.
Both the Pr123 and Pr124 compounds share insulating CuO2 planes and exhibit nosuperconductivity [7, 8]. The CuO single chains in Pr123 follow semiconducting
property but Pr124 has a metallic conduction along the CuO double chain block [9].
For Pr124, it is hard to control the carrier density of doped double chains, because itis thermally stable against high temperature heat treatment.
For Pr247 intermediate compound existing between Pr123 and Pr124 phases,
there are alternate stacks of CuO single-chain and double-chain blocks along thec-axis such as {-S-D-S-D-} sequence [10, 11] (see Figure 1). Here, CuO single-chain
and double-chain blocks along the b-axis are abbreviated as S and D, respectively.
Under thermal control of the oxygen content along the semiconducting CuO single
chains in Pr247, it is possible to investigate the physical characters of the metallic
CuO double chains. In oxygen defect polycrystalline sample, we succeeded in theappearance of superconductivity at an onset temperature T c,on of 15 K [5].
0The B-site substituted perovskite oxides A2 B0 B0 O6 have been widely studied
because of their attractive physical properties and potential applications [13] (seeFigure 2a). Some of the double perovskite compounds such as A2 FeMoO6
exhibiting negative tunneling magnetoresistance effect at room temperature are ofgreat interest with a wide range of applications in magnetic devices [14]. Furthermore, multiferroic double perovskite oxides have an effective coupling between
spontaneous ferroelectric polarization and ferromagnetic ordering, which is considered to be promising materials from view points of physics and its applications
0[15]. Recently, a series of double perovskite oxides Ba2 Ln0 Bi0 O6 (Ln:lanthanides)
has been examined on the view point of photocatalytic semiconductors for hydrogen generation by water splitting and are taken as alternative materials for TiO2oxide [16, 17]. In particular, Ba2 PrBiO6 is found to possess highly photocatalytic
performance, which is probably close to the valence mixing state [18, 19]. Furthermore, a previous study on the magnetic properties of the Ba2 PrBiO6 compound
revealed that the average valence of Pr ions is an intermediate state between
trivalent and tetravalent [20].
As for the key factors to fabricate visible light driven photocatalysts, it isdesirable to control the energy band gap between the valence and conduction bandsof their semiconductors to utilize a wide range of visible light [21, 22]. Accordingly,
we think that the Sb substitution at the B site of the parent material Ba2 PrBiO6 is aneffective approach to adjusting the band gaps. For high photocatalytic activity, we
avoid charge recombination between electron and hole and try to promote thephotogenerated charge separation in the photocatalystic materials [21, 23]. In our
research [24], it has been demonstrated that the valence mixing states between Pr3þand Pr4þ are closely related to the phenomena of charge separation.
For our further understanding of the enhanced effect of the mixed valence states
at B-site ions of the double perovskite compound on the photocatalytic

2

Functional Materials Synthesis and Physical Properties
DOI: http://dx.doi.org/10.5772/intechopen.100241

Figure 1.
(a) Typical crystal structure of Pr2 Ba4 Cu7 O15 δ (Pr247) with CuO single-chain and double-chain blocks
stacked along the c-axis. Here, S and D denote CuO single-chain and double-chain blocks along the b-axis. For
comparison, the crystal structure of Pr124 is shown on the right hand side. (b) TEM image of superconducting
Pr247. CuO single-chain and double-chain blocks are alternately stacked along the c-axis such as {-S-D-S-D-}
sequence [12].

performance, we demonstrate the 2-propanol decomposition and methylene blue(MB) degradation under the irradiation of visible right for Ba2 Tb(Bi,Sb)O6 samples
prepared by the citrate pyrolysis technique. MB aqueous solution is adopted as themodel pollutant [25].

2. Experiments
2.1 Double-chain based superconductor
2.1.1 Synthesis of Pr2 Ba4 Cu7 O15 δ samples
First of all, flow chart of citrate pyrolysis technique for the synthesis of
Pr2 Ba4 Cu7 O15 δ (sample #1) is illustrated in Figure 3b. We synthesized high-quality
polycrystalline samples of Pr2 Ba4 Cu7 O15 δ by using a citrate pyrolysis technique [2, 3].
Stoichiometric quantities of high purity Pr6 O11 , Ba(NO3 )2 , and CuO were mixed andthoroughly ground. The mixture was dissolved in a nitric acid solution at 50–60°C. Afteradding citric acid to the resultant solution, we then neutralized it by adding aqueous

3

Recent Perspectives in Pyrolysis Research

Figure 2.
(a) Typical crystal structure of double perovskite Ba2 (Pr,Tb)(Bi,Sb)O6 . (b) SEM image of Ba2 TbBiO6
polycrystalline film fabricated from the single-phase powders by an electrophoretic deposition technique.
(c) Photograph of the pelletized precursors of Ba2 TbBiO6 after a citrate pyrolysis procedure.

Figure 3.
(a)X-ray diffraction patterns of as-sintered polycrystalline Pr2 Ba4 Cu7 O15 δ . The (004) peak corresponds toone of typical Miller indexes of Pr247. The calculated curve is obtained using the lattice parameters in the text.
Inset shows characteristic peaks at 2θ  7°, indicating the formation of Pr123, Pr124, and Pr247 phases. (b)Flow chart of citrate pyrolysis technique for the synthesis of Pr2 Ba4 Cu7 O15 δ (sample #1). After post-annealingof the as-sintered sample in a vacuum, quenching procedure is needed to obtain higher superconductivity due tofurther oxygen defects.

4

Functional Materials Synthesis and Physical Properties
DOI: http://dx.doi.org/10.5772/intechopen.100241

ammonia. After the solution was dried up under stirring on halogen lamp heater block,the porous black products were formed through the self-ignition process of it. Finally,
the precursors were ground into fine powders and they were annealed under ambientpressure of flowing oxygen gas at 891°C 0:5°C for an extended period over 100120 h.
For the present citrate pyrolysis synthesis procedure, we adopted the electric tube
furnace with three zone temperature controlled system, to achieve the temperature
uniformity within 1°C. In our previous study [26], we realized homogeneous distributions of the superconducting grains and improved weak links between theirsuperconducting grains in the sintering procedure by using the 3 zone furnace. The
oxygen in the as-sintered sample was removed by reduction treatment in a vacuum at
500600°C, yielding a superconducting material. In particular, sample #1 wasquenched in air from 300°C down to room temperature and samples #2–1 and #2–2 were
slowly cooled in the electric furnace, as listed in Table 1. As mentioned below, thisquenching procedure is needed to obtain higher superconductivity due tofurther oxygen defects. Typical dimensions of the pelletized rectangular sample were4  3  1 mm3.
2.1.2 Structural and physical properties of Pr2 Ba4 Cu7 O15 δ samples
X-ray diffraction measurements on the produced samples were carried out atroom temperature with an Ultima IV diffractometer (Rigaku) using Cu-Kα radiation. We evaluated the lattice parameters from the x-ray diffraction patterns using
the least-squares fits.
The local crystal structure of the Pr247 sample was revealed by high-resolution
transmission electron microscopy (TEM) using a JEOL3010 microscope operated at
300 kV at Tohoku University, to examine alternative stacking along the c-axis
between CuO single-chain and double-chain blocks. The electric resistivity as afunction of temperature was measured by the dc four-terminal method using a
Gifford-McMahon cryocooler (Sumitomo heavy Industries).
We performed Hall coefficient measurements on the 48-h-reduced samples withthe five-probe technique using a physical property measuring system (PPMS,
Quantum Design), to check the sign of carriers in the present Pr247 superconductor. For determination of an onset temperature of superconductivity andsuperconducting volume fraction at low temperatures, the dc magnetization was
performed under zero-field cooling (ZFC) in a commercial superconducting quantum interference device (SQUID) magnetometer (MPMS, Quantum Design).
2.1.3 Pressure effect on transport properties of Pr2 Ba4 Cu7 O15 δ samples
It is well known that application of external pressure on oxide superconductors
changes doped carrier densities, causing a positive or negative dependence of theirSample no.

Reduced conditionδ

T c,on (K)T c,zero (K)Experimental data

#1

500°C 48 h, 600°C 24 h quenched

0.72

26

22

ρ(T), M(T)#2-1a

500°C 48 h furnace cooled

0.56

26.5

15

TEM

#2-2b

500°C 48 h furnace cooled

0.56

26.5

15

RH , pressure effectIn details, see the corresponding text and references. δ denotes oxygen deficiency.
aRef. [12].
Ref. [27].

bTable 1.
Sample details of Pr2 Ba4 Cu7 O15 δ used in the experiments.

5

Recent Perspectives in Pyrolysis Researchsuperconducting transition temperature. We carried out the temperature dependence of the resistivity and the magneto-resistance (MR), under a maximum pressure of 2 GPa.
The MR effect of Pr247 sample was measured at low temperatures as a functionof applied field up to 14 T using a 15 T-SM superconducting magnet at Institute forMaterials Research, Tohoku University. The electric current I was excited in thelongitudinal direction to the sample and the external magnetic field H was appliedin the transverse direction to it (H⊥I). We measured the influence of appliedpressure on the electric resistivity using a hybrid piston cylinder-type CuBe/NiCrAlcell under hydrostatic pressure up to 2.0 GPa, where inner and outer cylinders weremade of NiCrAl and CuBe alloys, respectively. A mixture of Fluorinert FC-70 and
FC77 (1:1) was used as a pressure transmitting medium in the experiments.
2.2 Double perovskite photocatalytic semiconductor
2.2.1 Synthesis of Ba2 Tb(Bi,Sb)O6 samples
The citrate pyrolysis technique as mentioned above was applied to synthesis of
Ba2Tb(Bi,Sb)O6 compounds. After mixing stoichiometric quantities of high purity Ba(NO3 )2 , Tb4 O7 , Bi2 O3 , and Sb, the resultant mixture was dissolved in a nitric acidsolution at 70–80°C. Furthermore, adding citric acid to the solution, the neutralizing
process was in progress by adding aqueous ammonia to it while the pH value of thesolution reached  6:9. The transparent solution was dried under stirring on the
halogen lamp hot plate, and the self-ignition process occurred in the 0.5 L beaker,
resulting in the formation of the porous products. Finally, the precursors were groundinto fine powders and they were annealed in air at 900–1000°C for 48-96 h, in orderto synthesize the Ba2 Tb(Bi,Sb)O6 double perovskite phase (samples #T1 and #T2).
For scanning electron microscope (SEM) measurements, Ba2 TbBiO6 polycrystalline film on Ag substrate was fabricated from the single-phase powders by anelectrophoretic deposition technique. The SEM image revealed the surface
morphology and shape of the Ba2 TbBiO6 powder sample.
2.2.2 Physical properties of Ba2 Tb(Bi,Sb)O6 samples
We measured optical spectra by a diffuse reflectance method using a spectrophotometer (Hitachi U-3500) with the reference material of BaSO4 . The energy
band gaps for the powder samples were estimated from the reflectance data on thebasis of conventional Kubelka-Munk function [18, 28]. The dc magnetization measurement was performed over a wide range of temperatures under the magnetic
field cooling process of 0.1 T using a SQUID magnetometer.
The effective magnetic moment (μeff ) estimated from the the magnetic susceptibility data using the Curie–Weiss law gives rise to the average valence of the Tb
ion at the B site, which is related to the ratio of the Tb3þ and Tb4þ ions.
2.2.3 Photocatalytic properties of Ba2 Tb(Bi,Sb)O6 samples
We conducted the gaseous 2-propanol (IPA) and methylene blue (MB) degradation experiments, to evaluate photocatalytic activities of the powder samples (indetail, refer to [18, 29]). The visible light radiation experiment started after the IPA
gas concentration reached constant under the dark condition. This conformationsuggested that the IPA gas finished absorbing on the surface of powders. We used a
300 W Xe lamp equipped with UV and IR filtering functions (Cermax LX300F,
6

Functional Materials Synthesis and Physical Properties
DOI: http://dx.doi.org/10.5772/intechopen.100241

Figure 4.
(a) Photocatalytic activities of IPA decomposition vs visible light irradiation time for Ba2 TbBiO6 citratepyrolysis and solid-state samples. For comparison, the data for the Sb50% substituted sample are given. The
gaseous concentration is normalized by the surface area of the powder samples. (b) Illuminating spectra of theXe lamp limited in the visible wavelength range between 390 and 780 nm. (c) Photograph of 0.5-L glass
reactor vessel for the IPA experiment. The powder sample (about 1 g) placed on the bottom of a small glass cell
was set in its vessel.

Excelitas Technologies). The illuminating spectra of the Xe lamp covered the visible
wavelength range from 390 to 780 nm (Figure 4b). We set the powder samples(about 1 g) placed on the bottom of a small glass cell in a 0.5-L glass reactor vessel(Figure 4c) and injected the dilute IPA gas (5 cc) into its vessel with a syringe.
It is well known that the IPA gas under photocatalytic reaction is finallydecomposed into CO2 [29]. Accordingly, the CO2 concentration was measured as afunction of irradiation time using a gas chromatography system (GC-2014, ShimazuCo.). The photocatalytic methylene blue degradation was carried out using 0.5 g of
powders suspended in 50 mL of MB solution (10 ppm). The MB solution was stirredin dark for 30 min before starting visible light radiation. The bleaching of MB was
measured using the UV–visible spectrometer (V550, JASCO Co.). The solution of
about 3 mL was transferred from the 100 mL reactor vessel under light irradiationand it was then analyzed at the regular time interval, to determine thecorresponding MB concentration.

3. Results and discussion
3.1 Double-chain based superconductor Pr2 Ba4 Cu7 O15 δ
3.1.1 Structural and superconducting properties of Pr2 Ba4 Cu7 O15 δ
X-ray diffraction data revealed that the as-sintered polycrystalline samples are
an almost single phase with an orthorhombic structure (Ammm), as shown in
Figure 3a. The lattice parameters of the as-sintered sample prepared using thethree-zone controlled furnace are a ¼ 3:8919 Å, b ¼ 3:9143 Å, and c ¼ 50:7927 Å.
7

Recent Perspectives in Pyrolysis Research

These values fairly agree with the lattice parameters of Pr247 estimated by aprevious study [30]. It was from gravimetric analysis estimated that the oxygen
deficiencies in the 48 and 72 h reduced samples in a vacuum are δ ¼ 0:56 and δ ¼
 0:72, corresponding to samples #2–1, #2–2 and sample #1, respectively (Table 1).
According to a variation in T c as a function of the oxygen deficiency [31], the T c,onshows a rapid increase at δ ≥  0:2, then follows a stable increase with δ, and finallyremains saturation around 26–27 K at δ ≥  0:6. Therefore, we conclude that the
doped carrier concentrations in the present samples are located near the optimally
doped region.
First of all, the temperature dependences of electric resistivities of the Pr123,
Pr124, and as-sintered Pr247 compounds are shown in Figure 5a. The Pr123 andPr124 samples exhibit semiconducting and metallic behaviors in ρ. The as-sintered
Pr247 sample shows a weakly semiconducting property at high temperatures, itthen reaches a maximum peak at intermediate tempertures around  150 K, andfinally it follows a metallic behavior with lowering T. It is well known that CuO
single chains in Pr123 and CuO double chains in Pr124 show semiconducting andmetallic behaviors, respectively. The reduction heat treatment on the as-sinteredsample in a vacuum results in the appearance of superconducting state withT c =22-27 K, accompanied by the strongly metallic properties over a wide range oftemperature (Figure 6a). For the present Pr247 sample with a reduction treatment
for 72 h, a sharp superconducting transition appears at an onset temperature
T c,on =26 K and then it achieves a zero resistance state at T c,zero =22 K.
Furthermore, to check bulk superconductivity, we performed to measure lowtemperature dependence of magnetic susceptibility χ of the 72-h-reduced
superconducting sample measured at 5 mT under ZFC scan. Figure 6b exhibits
diamagnetic signals below T c,on = 26 K for the 72-h-reduced sample. In addition,
the superconducting volume fraction due to the shielding effect is estimated to be 58% from the ZFC values at 5 K. In the inset of Figure 6, the magnified data areplotted to clarify the definition of T c,on . We note that the quenching procedure in

Figure 5.
(a) Temperature dependences of electric resistivities of the Pr123, Pr124, and as-sintered Pr247 compounds.
(b) Schematic view of Cu(3dx2 y2 ) orbitals and O(2pσ ) orbitals in a CuO double chain of Pr2 Ba4 Cu7 O15 δ .
Here, tpp and tdd denote the hoping term between 2pσ orbitals at the nearest neighbor oxygen sites and thatbetween 3dx2 y2 orbitals at the nearest neighbor copper sites, respectively [32].

8Functional Materials Synthesis and Physical Properties
DOI: http://dx.doi.org/10.5772/intechopen.100241

Figure 6.
(a) Temperature dependence of electric resistivity of the 72-h-reduced superconducting Pr247 compound.
(b) Low-temperature dependence of magnetic susceptibility χ of the 72-h-reduced superconducting sample
measured at 5 mT under ZFC scan. In the insets, the magnified data are plotted to clarify the definition of T c,on .

air promotes a sharp superconducting transition appearing at temperatures between
T c,on =26 K and T c,zero =22 K.
3.1.2 Hall and pressure effects of Pr2 Ba4 Cu7 O15 δ
Furthermore, in Figure 7, we show the temperature dependences of the Hall
coefficients RH for the as-sintered non-superconducting and 48-h-reduced
superconducting samples of Pr2Ba4Cu7 O15 δ. For comparison, the RH values of the assintered sample are taken from our previous work [33], which are similar, in magnitude and temperature dependence, to RH of Pr124 with a metallic CuO double-chain
block. (Figure 1a) For the 48-h-reduced sample, the RH data exhibit negative values
in the limited temperature range between 30 and 100 K, accompanied by electron
doping due to the reduced heat treatment in a vacuum. Moreover, we estimate RH ¼
1:1  10 3 cm3/C at 30 K, which is in good agreement with the published data [33].
In Figure 7b, we show the temperature dependences of electrical resistivities of
the 48-h-reduced superconducting sample under hydrostatic pressures up to
2.0 GPa. The application of external pressure on the 48-h-reduced sample
suppressed the superconductivity with increasing the applied pressure. In the case9

Recent Perspectives in Pyrolysis Research

Figure 7.
(a) Temperature dependences of Hall coefficients for the as-sintered non-superconducting and 48-h-reduced
superconducting Pr247 compounds. For comparison, the as-sintered data are cited from our previous paper[34]. (b) Temperature dependences of electrical resistivities of the 48-h-reduced superconducting Pr247 undervarious pressures up to 2.0 GPa. (c) Magneto-resistance effect (up to 14 T) of the 48-h-reduced
superconducting Pr247 for temperatures close to 30 K under a maximum pressure of 2.0GPa.

of applied pressures above 0.8 GPa, the zero-resistance state vanished and the hightemperature metallic properties were transferred to the semi-conducting behaviors,
accompanied by a rapid increase in ρ. The onset temperature of superconducting
transition T c,on declined gradually from 26.5 K at ambient pressure through 24.1 K
at 0.8 GPa down to 18.0 K at 1.6 GPa. However, the onset temperature wasenhanced up to  30 K under a maximum pressure of 2.0 GPa.
The electronic phase diagram between normal and superconducting phases of a
CuO double chain model has been clarified using the Tomonaga-Luttinger Liquid
theory [32]. In the case of a shrinkage of the lattice spacing along c-axis between thetwo single chains of a CuO double-chain block, we expect the enhancement of bothcarrier hopping energies, tpp and tdd . Here, we define the hoping term between 2pσ
orbitals at the nearest neighbor oxygen sites and that between 3dx2 y2 orbitals at thenearest neighbor copper sites, as tpp and tdd , respectively (see Figure 5b). If weapply the external pressure on Pr247 including the CuO double chain block, it istheoretically predicted that the pressure induced enhancement of the hopping
terms will result in a phase transition from the superconducting to normal phase.
This theoretical prediction is qualitatively in agreement with the negative pressure
effect on the superconducting phase observed in Pr247 [34].
We examined the magneto-resistance effect (up to 14 T) of the 48-h-reduced
superconducting Pr247 for temperatures close to 30 K under a maximum pressureof 2.0 GPa, to establish a phase boundary between the superconducting and normal
states. In Figure 7c, the MR data around 30 K tend to increase according to the
upward covey behaviors at low fields. On the other hand, the MR around 40 K
shows weak increases in the downward convey forms which is related to the model
10

Functional Materials Synthesis and Physical Properties
DOI: http://dx.doi.org/10.5772/intechopen.100241

of slightly warped Fermi surfaces. (in details, see [27]) This finding indicates thatthe applied magnetic field destroyed the superconducting isolated regions andenlarged further the normal-state majority phase, resulting in the observed MR
phenomena near 30 K. The re-entrant superconducting behavior observed at
2.0 GPa is an open question to be resolved in future through the structure analysis
under applied pressures [35].
3.2 Double perovskite photocatalytic semiconductor
3.2.1 Structural and valence-state properties of Ba2 Tb(Bi,Sb)O6 samples
X-ray diffraction patterns of Ba2 TbBiO6 are shown in Figure 8. For the parent
Ba2 TbBiO6 with a monoclinic structure (the space group I2=m), the lattice parameters were estimated from the x-ray diffraction data to be a ¼ 6:1099 Å, b ¼ 6:0822
Å, c ¼ 8:5939 Å and β ¼ 89:888∘ , which fairly agree with previous data [20]. The
peak intensity of (101) reflection (the inset of Figure 8) is responsible for the
degree of B-site ordering in the double-perovskite crystal structures. When the Bsite ordering is assumed to be 70 %, the tiny profiles around the (101) peak arewell fitted by the least squared method using the RIETAN-FP program [37].
For the Ba2 Pr(Bi,Sb)O6 system, the polycrystalline samples for x < 0:5 areformed in almost single phases of the monoclinic structure, while the x ≥ 0:5 samples crystallize in a cubic structure with the space group Fm3m [24]. Substitution of
the smaller Sb5þ (0.60 Å) ion at the Bi5þ (0.76 Å) site causes a monotonic decreasein the lattice parameters. For Ba2 TbBi0:5 Sb0:5 O6 , we obtain the lattice parameters
a ¼ 8:4511 Å and α ¼ 90∘ . Figure 8b shows tolerance factor vs. Sb content (x) for
2þ
4þ
3þ 5þ
3þ 5þ
5þ
4þ
4þ
4þ
Ba2þ
2 Tb Bi1 x Sbx O6 and Ba2 Tb M11 x M2x O6 with M1 = Bi0:5 Bi0:5 andFigure 8.
(a)X-ray diffraction patterns of Ba2 TbBiO6 . Inset shows the enlarged diffraction data. The emergence of (101)reflection indicates B-cation ordering which is characteristic of the ordered double-perovskite structure. (b)3þ 5þ5þTolerance factor vs Sb content for Ba2 TbBi1 x Sbx O6 . The solid and dotted lines denote Ba2þ
2 Tb Bi1 x Sbx O6
5þ
5þ
4þ
3þ
4þ
4þ
4þ
4þ
3þ
and Ba2þ
2 Tb M11 x M2x O6 with M1 = Bi0:5 Bi0:5 and M2 =Sb0:5 Sb0:5 . The crystallographic phase
diagram consisting of the monoclinic, rhombohedral and cubic phases is given as a function of tolerance factor inref. [36].

11Recent Perspectives in Pyrolysis Research5þM24þ = Sb3þ
0:5 Sb0:5 . The tolerance factor of double perovskite compounds Ba2 (Pr,Tb)(Bi,Sb)O6 is given by the following equation,rBa þ rO,
t ¼ pﬃﬃﬃrTb þrM
2 2 þ rO

(1)

where rBa , rO , rTb , and rM¼ðBi,SbÞ are the ionic radii of the respective ions (indetails, refer to [24]). The crystallographic phase diagram consisting of the monoclinic, rhombohedral and cubic phases is given as a function of tolerance factor inref. [36]. The crystal structures obtained for the x = 0 and x = 0.5 samples arealmost consistent with the phase diagram reported. Assuming the tetravalent stateof Tb4þ , we obtain the value of t = 0.97914, indicating the stability of a cubic
structure for the x = 0.5 sample. The microstructures and pelletized precursors for
the Ba2TbBiO6 parent sample prepared by the citrate pyrolysis method are shown in
Figure 2b and c. The crystalline grains of the citrate sample have an average size
ranging from about 0.2 to 0.5 micron. On the other hand, the grain diameters of thesolid-sate sample are distributed on a micron order scale and about one-order grater
than those of the former. The citrate pyrolysis process fabricates uniformly
dispersed grains with sub micron size compared with the solid-state preparation
technique (see [24]).
The magnetic susceptibility data for the Ba2 Tb(Bi1 x ,Sbx ) O6 compounds (x=0
and 0.5) were measured as a function of temperature under a magnetic field of
0.1 T. (not shown here) The effective magnetic moments (μeff ) are estimated fromthe magnetization data using the Curie–Weiss law. For the parent and x = 0.5 citratesamples, we obtain μeff = 8.91 μB and 8.86 μB , as listed in Table 2. Moreover, we try
to evaluate the ratio of the Tb3þ and Tb4þ ions using the equation,
μ2eff ¼ yμ2eff Tb3þ þ ð1yÞμ2eff Tb4þ(2)

where μeff (Tb3þ ) = 9.72 μB and μeff (Tb4þ ) = 7.94 μB . For the parent and x = 0.5
citrate samples, we obtain that the ratio of Tb3þ and Tb4þ ions is 0.52 : 0.48 and 0.49 :
0.51, respectively. The mixed valence state expected from the magnetic data qualitatively consists with the above discussion on the stability of cubic structure for thex = 0.5 sample. The magnetic data suggest that about half of Re ions (Re = Pr and Tb)
Sampleno.

cComposition

Synthetic
methodCrystalsymmetry

μeff (μB )Experimental
data

#T1

Ba2 TbBiO6

citrate pyrolysis

monoclinic

8.91

IPA, MB, Opt.

#T2

Ba2 TbMO6 M = Bi0:5
Sb0:5

citrate pyrolysis

cubic

8.86

IPA, MB, Opt.

#T3

Ba2 TbBiO6

solid statemonoclinic

9.07

IPA, MB, Opt.

#P1

Ba2 PrBiO6

citrate pyrolysis

monoclinica

3.08a

MB

a

MB

3.15b

MB

a

#P2

Ba2 PrSbO6

citrate pyrolysis

cubic

#P3

Ba2 PrBiO6

solid statemonoclinicb

3.0

The effective magnetic moments μeff were estimated from the magnetization data using the Curie–Weiss law. IPA, MB
and Opt. denote gaseous 2-propanol decomposition, methylene blue degradation, and optical measurements,
respectively.
aRef. [24].
bRef. [38].

Table 2.
Sample details of Ba2 (Pr,Tb)(Bi,Sb)O6 used in the experiments.

12

Functional Materials Synthesis and Physical Properties
DOI: http://dx.doi.org/10.5772/intechopen.100241

are oxidized to the tetravalent state over the whole range of Sb substitution [24]. In aprevious analysis of X-ray photoemission spectroscopy [39], it has been shown that a
predominant peak of Pr3þ coexists with a smaller shoulder structure of Pr4þ , giving
further evidence for the mixed valence state of the Pr ion.
3.2.2 Photocatalytic and optical properties of Ba2 Tb(Bi,Sb)O6 samples
Next, the visible-light induced decomposition experiment using IPA gas was
carried out, to examine photocatalytic activities of the powder samples.
In Figure 4a, the temporal variation of evolved CO2 concentration after visible
light irradiation are shown for the Ba2 TbBiO6 citrate and solid state samples. For
comparison, the data for the Sb50% substituted Ba2 Tb(Bi0:5 ,Sb0:5 )O6 sample arealso given. The CO2 concentrations for both the citrate and solid state x = 0 samples
rapidly rise at the initial 20 min and then show a gradual increase at further
illumination time. For the Sb50% substituted sample, no clear evolution of CO2 wasdetected. It is expected that the heavy substitution of Sb ion at the B-site causes theband gap opening and considerably reduces the formation of electron–hole pairs,
resulting in a strong suppression of the photocatalytic reaction processes. In ourprevious study [38], we investigated the influence of the band gap opening due tothe Sb substitution on the basis of first-principles electric structure calculation. The
Sb substitution at Bi site removes the Bi-orbitals and makes the corresponding band
gap enlarged. The photocatalytic activity exhibits strong dependence of the Sb
substitution, which is associated with the enhancement of the band gap energy. It istrue that the photocatalytic behavior for the solid state sample is similar to that of
the citrate sample. However, the evolved CO2 quantities of the x=0 citrate sample
are about twice as large as the data of the corresponding solid state sample, as
shown in Figure 4a. The improved photocatalytic activity of the Ba2 TbBiO6 citratesample is attributed to its morphology, where fine polycrystalline grains with a sub
micron order are homogeneously dispersed.
Furthermore, we demonstrated photocatalytic degradation of methylene blue(MB) vs. visible light irradiation time for the end-member samples with Ba2 (Pr,Tb)
BiO6 and Ba2 PrSbO6 compositions. For comparison, the MB data of the Ba2 PrSbO6
solid-state sample are given. Here, the MB degradation rate (%) is given byðCð0Þ CðtÞÞ=Cð0Þ  100, where the peak intensities located around λ = 665 nm at
the initial and final concentrations at different time intervals are defined as C(0)and C(t), respectively. Figure 9a shows the MB degradation rate after the visible
light irradiation for Ba2 PrBiO6 and Ba2 PrSbO6 samples. In Figure 9b and c, thetypical absorbance spectra and corresponding MB solutions for Ba2 PrSbO6 at different irradiation time intervals are also displayed. The MB degradation rates undervisible light irradiation show rapid increases due to Sb-substitution. For the Sb50%
substituted Ba2 Tb(Bi0:5 ,Sb0:5 )O6 sample, the highest performance of MB degradation was observed. The citrate parent sample of Ba2 PrSbO6 exhibits higher degradation in comparison with the data of the solid-state sample with the identicalcomposition. For Ba2 PrBiO6 , the effect of Sb-substitution on the photocatalytic
degradation of MB is in direct contrast to that on the IPA decomposition undervisible light irradiation.
Finally, we carried out the optical measurements on the Ba2 Tb(Bi1 x ,Sbx )O6(x=0 and 0.5) powder samples by the diffuse reflectance method. In the first step,
we transformed the observed reflectance data to the absorption coefficient αKM byapplying the conventional Kubelka-Munk function. In the next step, extrapolating
the tangent line to the εp axis near the band edge, we evaluate the energy band gap
from the intersection following the equation
13

Recent Perspectives in Pyrolysis Research

Figure 9.
(a) Photocatalytic degradation of methylene blue (MB) vs visible light irradiation time for Ba2 (Pr,Tb)(Bi,Sb)
O6 citrate pyrolysis samples. For comparison, the MB data of the Ba2 PrSbO6 solid-state sample are given.
(b) Absorbance spectra as a function of visible light irradiation time for the MB degradation in the case of
Ba2 PrSbO6 citrate pyrolysis sample. (c) Photocatalytic variations of the MB solutions at different irradiation
time intervals.

Figure 10.
2(a) Optical properties of Ba2 Tb(Bi1 x ,Sbx ) O6 (x=0 and 0.5). αKM εp vs εp for the x ¼ 0:5 sample are1=2
vs εp . For the x = 0 sample, Eg is estimated fromplotted as a function of εp . The inset shows plots of αKM εpan intersection point of base line and straight line by extrapolation. (b) Band gap energies vs Sb content (x) for
Ba2 Tb(Bi1 x ,Sbx ) O6 (x=0 and 0.5). The data of Ba2 Pr(Bi,Sb)O6 are cited from our previous work [24]. (c)Schematic illustration between the semiconductor band positions and the the surface redox reactions inphotocatalysis. The valence band (VB) is located to facilitate oxidation, but the lower conduction band (CB1)
is not sufficiently positioned to facilitate reduction. The higher conduction band (CB2) is suitable for promoting
effective reduction process.

14

Functional Materials Synthesis and Physical Properties
DOI: http://dx.doi.org/10.5772/intechopen.100241



αεp

n


∝ εp


Eg ,

(3)

where α, εp , and Eg are the absorption coefficient, the photon energy, and theband gap energy. The exponents, n ¼ 2 and n ¼ 1=2, are responsible for direct andindirect optical transitions, respectively [18, 19]. In Figure 10a, the absorption2
coefficient, αKM εp is plotted as a function of εp for the x=0.5 sample. In the inset
1=2
vs. εp are shown for the x=0 sample. We obtain thatof Figure 10a, αKM εp
Eg = 0.92 eV at x=0 and 2.45 eV at x=0.5, assuming indirect and direct photontransitions, respectively. The magnitude of the energy band gap is enhanced due tothe Sb substitution.
In Figure 10c, schematic view between the semiconductor band positions andthe the surface redox reactions in photocatalysis is presented. The valence band
(VB) is located to facilitate oxidation, but the lower conduction band (CB1) is not
sufficiently positioned to facilitate reduction. The higher conduction band (CB2) isneeded to promote reduction process. Applying the present band model to thephotocatalytic activities observed for Ba2 Tb(Bi,Sb)O6 , the parent compounds withsmaller energy band gap of nearly 1 eV are responsible for the lower energy level of
conduction band (CB1) edge. On the other hand, from the effect of band gap
opening due to Sb substitution, we believe that the CB2 band model is valid in theheavily Sb substituted samples. The former is closely related to facilitate oxidation
reactions at the surface for the IPA decomposition process. In the latter compoundswith the larger energy band gaps of 2.5 eV, the MB degradation is strongly
promoted in contrast to that of the former compounds. These findings indicate thatthe conduction band edge of the heavily Sb substituted samples is optimized.

4. Conclusions
A citrate pyrolysis technique is a unique route to prepare reactive precursor
mixtures through an ignition process of concentrated aqueous solution including
metallic ions of stoichiometric composition. This procedure enables to synthesize
highly homogeneous and fine powders for functional materials. The double-chain
based superconductor Pr2 Ba4 Cu7 O15 δ and double perovskite photocatalytic
semiconductor Ba2 Tb(Bi,Sb)O6 were synthesized by using the citrate pyrolysis
technique.
The TEM image of the 48-h-reduced Pr247 revealed that CuO single-chain anddouble-chain blocks are alternately stacked along the c-axis such as {-D-S-D-S-}
sequence. For the present Pr247 sample with a reduction treatment for 72 h, a sharp
superconducting transition appeared at an onset temperature T c,on =26 K accompanied by a zero-resistance state at T c,zero =22 K. The superconducting volume fraction
estimated from the magnetization measurement reached an excellent value of 58%. Both reduction treatment in a vacuum and subsequent quenching procedure
are needed to realize higher superconductivity due to further oxygen defects. For
the 48-h-reduced sample, the RH data exhibited negative values in the limited
temperature range between 30 and 100 K, accompanied by electron doping due tothe reduced heat treatment in a vacuum. The re-entrant superconducting behavior
observed at 2.0 GPa is an open question to be resolved in future through detailed
structure analysis under applied pressures.
The polycrystalline samples for Ba2 Tb(Bi1 x ,Sbx )O6 (x ¼ 0 and 0.5) wereformed in the monoclinic and cubic crystal structures. The magnetic data suggestthat about half of Tb ions are oxidized to the tetravalent state over the wide range ofSb substitution, which is a common trend in the case of Ba2 Pr(Bi,Sb)O6 . For Ba2 Tb
15

Recent Perspectives in Pyrolysis Research(Bi1 x ,Sbx )O6 , we estimated Eg = 0.92 eV at x=0 and 2.45 eV at x=0.5, assuming
indirect and direct photon transitions, respectively.
We conducted the gaseous 2-propanol (IPA) and methylene blue (MB) degradation experiments under a visible light irradiation, to evaluate photocatalytic
activities of the powder samples. The band gap opening due to the heavy Sb substitution suppresses the formation of electron–hole pairs, causing a decrease of thephotocatalytic reaction processes in the IPA decomposition. The MB degradation
rates under visible light irradiation show rapid increases due to Sb-substitution. For
the Sb50% substituted Ba2 Tb(Bi0:5 ,Sb0:5 )O6 sample, the highest performance of MB
degradation was observed. In the Ba2 (Pr,Tb)(Bi,Sb)O6 system, the effect of Sbsubstitution on the photocatalytic degradation of MB is in direct contrast to that on
the IPA decomposition under visible light irradiation. We conclude that the citratepyrolysis samples of Ba2 Tb(Bi,Sb)O6 exhibit excellent performances in comparison
with the data of the solid-state samples with the identical composition. The
enhanced photocatalytic properties in the citrate samples are attributed to theirmorphology, where fine particles are homogeneously distributed with a sub micron
order.

Acknowledgements
This work was supported in part by MEXT Grands-in-Aid for Scientific Research(JPSJ KAKENHI Grants No. JP19K04995). We thank A. Sato, T. Teramura, and
Y. Nakarokkaku for their supports in experiments.

Author details
Tatsuya Senzaki1, Michiaki Matsukawa1*, Takanori Yonai1, Haruka Taniguchi1,
Akiyuki Matsushita2, Takahiko Sasaki3 and Mokoto Hagiwara4
1 Faculty of Science and Engineering, Iwate University, Morioka, Japan
2 National Institute for Materials Science, Tsukuba, Japan
3 Institute for Materials Research, Tohoku University, Sendai, Japan
4 Kyoto Institute of Technology, Kyoto, Japan*Address all correspondence to: matsukawa@iwate-u.ac.jp© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the termsof the Creative Commons Attribution License (http://creativecommons.org/licenses/
by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,provided the original work is properly cited.
16

Functional Materials Synthesis and Physical Properties
DOI: http://dx.doi.org/10.5772/intechopen.100241

References[1] L. A. Chick, L. R. Pederson, G. D.

[12] T. Konno, M. Matsukawa, H.

Maupin, J. L. Bates, L/ E. Thomas, G. J.
Exarhos, Materials Letters, vol. 10, 6-12,
1990.

Taniguchi, J.Echigoya, A. Matsushita,
M. Hagiwara, T. Miyazaki, K. Sano, Y.
Ono, Y. Yamada, T. Sasaki, and Y.
Hayasaka, Physica C521-522 (2016) 13.

[2] K. Koyama, A. Junod, T. Graf, G.

Triscone, and J. Muller, Physica C,vol.185-189, 66-70, 1991.

[13] S. Vasala, and M. Karppinen, Prog.

[3] M. Hagiwara, T. Shima, T. Sugano, K.

Koyama, and M. Matsuura, Physica C,
vol. 445-448, 111-114, 2006.

[14] K. -I. Kobayashi, T. Kimura, H.
Sawada, K. Terakura, and Y. Tokura,
Nature, vol. 395, pp. 677, 1998.

[4] M. Uehara, T. Nagata, J. Akimitsu, H.

[15] R. Ramesh, and N. A. Spaldin,

Solid State Chem., vol. 43, pp. 1-31, 2015.

Takahashi, N. Mori, and K. Kinoshita, J.
Phys. Soc. Jpn. 65 (1996) 2764.

Nature Materials, vol. 2, pp. 21, 2007.

[5] M. Matsukawa, Y. Yamada, M.

vol. 238, pp. 37, 1972.

Chiba, H. Ogasawara, T. Shibata, A.
Matsushita, and Y. Takano, Physica C
411 (2004) 101.

[17] H. W. Eng, P. W. Barnes, B. M.

[6] S. Watanabe, Y. Yamada and S.

Sasaki, Physica C 426-431 (2005) 473.
[7] L. Soderholm, K. Zhang, D. G. Hinks,

M. A. Beno, J. D. Jorgensen,C. U. Segre,
I. K. Schuller, Nature 328 (1987) 604.
[8] S. Horii, Y. Yamada, H. Ikuta, N.
Yamada, Y. Kodama, S. Katano,Y.
Funahashi, S. Morii, A. Matsushita, T.
Matsumoto, I. Hirabayashi, and U.
Mizutani, Physica C 302 (1998) 10.
[9] T. Mizokawa, C. Kim, Z. -X. Shen, A.

Ino, T. Yoshida, A. Fujimori, M. Goto, H.
Eisaki, S. Uchida, M. Tagami, K. Yoshida,
A. I. Rykov, Y. Siohara, K. Tomimoto, S.
Tajima, Yuh Yamada, S. Horii, N. Yamada,
Yasuji Yamada, and I. Hirabayashi, Phys.
Rev. Lett. 85 (2000) 4779.
[10] P. Bordet, C. Chaillout, J. Chenavas,

J. L. Hodeau, M. Marezio,J. Karpinski,
and E. Kaldis, Nature 334 (1988) 596.
[11] Y. Yamada, S. Horii, N. Yamada, Z.

Guo, Y. Kodama, K. Kawamoto,U.
Mizutani, and I. Hirabayashi, Physica C
231(1994)131.
17[16] A. Fujishima, and K. Honda, Nature,

Auerand, and P. M. Woodward, J. Solid
State Chem., vol.175, pp. 94, 2003.
[18] T. Hatakeyama, S. Takeda, F.

Ishikawa, A. Ohmura, A. Nakayama, Y.
Yamada, A. Matsushita, and J. Yea, J.
Cer. Soc. Jpn., vol. 118, pp.91-95, 2010.
[19] A. Matsushita, T. Nakane, T. Naka,

H. Isago, Y. Yamada, and Yuh Yamada,Jpn. J. Appl. Phys., vol. 51, pp. 121802-15, 2012.
[20] William T. A. Harrison, K. P. Reis,

A. J. Jacobson, L. F. Schneemeyer, and J.
V. Waszczak, Chem. Mater., vol. 7,
pp. 2161-2167, 1995.
[21] X. Chen, S. Shen, L. Guo, and S.

Mao, Chem. Rev. vol.110, 6503-6570,
2010.
[22] D. Sudha, and P. Sivakumar,

Chemical Engineering and Processing,vol. 97, 112–133, 2015.

[23] B. Ohtani, Catalysts, vol.3, 942-953,
2013.
[24] A. Sato, M. Matsukawa, H.

Taniguchi, S. Tsuji, K. Nishidate, S.

Recent Perspectives in Pyrolysis Research

Aisawa, A. Matsushita, and K. Zhang,
Solid State Science, 107, 10635, 2020.

[37] F. Izumi and K. Momma, Solid State
Phenom. 130 (2007) 15.

[25] A. Housa, H. Lachheb, M. Ksibi, E.
Elaloui, C. Guillard, J.M. Herrmann,
Applied Catalysis B31, 145, 2001.

[38] H. Taniguchi, M. Matsukawa, K.
Onodera, K. Nishidate, and A.
Matsushita, IEEE Transactions on
Magnetics, 55(2), (2019) 2400404.

[26] K. Honnami, M. Matsukawa, T.
Senzaki, H. Taniguchi, K. Takahashi, T.
Sasaki, M. Hagiwara, Physica C585
(2021) 1353869.
[27] M. Kuwabara, M. Matsukawa, K.
Sugawara,H. Taniguchi, A. Matsushita,
M. Hagiwara, K. Sano, Y. Ono, and T.
Sasaki, J. Phys. Soc. Jpn. 85 (2016)
124704.
[28] J. W. Tang, Z. G. Zou, and J. H. Ye,

J. Phys. Chem. C, vol. 111,
pp. 12779-12785, 2007.
[29] T. Murase, H. Irie, and K.
Hashimoto, J. Phys. Chem. B, vol. 108,
15803-15807 (2004)[30] Y. Yamada and A. Matsushita,

Physica C 426-431 (2005) 213.
[31] M. Hagiwara, S. Tanaka, T. Shima,

K. Gotoh, S. Kanda, T. Saito, and K.
Koyama, Physica C 468 (2008) 1217.
[32] K. Sano, Y. Ono, and Y. Yamada, J.

Phys. Soc. Jpn., 74 (2005) 2885.
[33] J. Tada, M. Matsukawa, T. Konno, S.

Kobayashi, M. Hagiwara, T. Miyazaki,
K. Sano, Y. Ono, and A. Matsushita, J.
Phys. Soc. Jpn. 82 (2013) 105003.
[34] F. Ishikawa, K. Fukuda, S. Sekiya, A.
Kaeriyama, Y. Yamada and A.
Matsushita, J. Phys. Soc. Jpn., 76 (2007)
Suppl. A 92.
[35] H. Taniguchi, A. Nakayama, M.

Matsukawa, S. Nakano, M. Hagiwara
and T. Sasaki, J. Phys. Soc. Jpn. 90(2021) 015001.

[36] S. Otsuka, and Y. Hinatsu, J. Solid

State Chem., vol. 227, pp. 132-141, 2015.
18[39] K. Onodera, T. Kogawa, M.

Matsukawa, H. Taniguchi, K. Nishidate,
A. Matsushita, and M. Shimoda, J. Phys.
Conf. Ser., vol. 969, pp. 012122-1-6,
2018.