New PbTiO3-Type Giant Tetragonal Compound Bi2ZnVO6 and Its

Feb 20, 2015 - Runze Yu , Narumi Matsuda , Ken Tominaga , Keisuke Shimizu , Hajime Hojo , Yuki Sakai , Hajime Yamamoto , Kengo Oka , and Masaki ...
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New PbTiO3‑Type Giant Tetragonal Compound Bi2ZnVO6 and Its Stability under Pressure Runze Yu,*,† Hajime Hojo,† Kengo Oka,†,‡ Tetsu Watanuki,§ Akihiko Machida,§ Keisuke Shimizu,† Kiho Nakano,† and Masaki Azuma*,† †

Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori, Yokohama 226-8503, Japan Department of Applied Chemistry, Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan § Quantum Beam Science Center, Japan Atomic Energy Agency, Sayo, Hyogo 679-5148, Japan ‡

S Supporting Information *

ABSTRACT: A new PbTiO3-type compound, Bi2ZnVO6, with a giant tetragonal distortion of c/a = 1.26 (a = 3.7869(3) Å, c = 4.7660(7) Å) was synthesized under high pressure−high temperature conditions (9 GPa and 1373 K). A point charge model calculation based on the atomic positions refined by Rietveld analysis of synchrotron X-ray diffraction (SXRD) data gave an electrical ionic polarization of 126 μC/cm2, the largest value among PbTiO3type perovskite compounds. The tetragonality (c/a) decreased with increasing temperature from 100 to 570 K without any trace of a phase transition. Instead, a pressure-induced transition from a polar tetragonal structure to a paraelectric GdFeO3 one accompanied by a 2.4% volume collapse was observed at 6.01 GPa. Bi2ZnVO6 showed paramagnetic behavior with S = 1/2 because of the random distribution of nonmagnetic Zn2+ and magnetic V4+ ions. Transport measurements indicated semiconductivity with an activation energy of 0.43 eV.

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INTRODUCTION PbTiO3 is a typical ferroelectric material with a large spontaneous polarization resulting from displacement of the B-site ion of ABO3 perovskite from the center of the octahedron leading to a pyramidal rather than octahedral coordination. This distorted structure is stabilized by the 6s2 lone electron pair of the Pb2+ ion and by hybridization between the Pb 6s and O 2p orbitals. 1,2 PbTiO 3 constitutes PbZrxTi1−xO3 (PZT), which shows outstanding piezoelectric properties at the morphotropic phase boundary (MPB) with the PbZrO3-based rhombohedral phase.3−8 Because of the growing concern about lead toxicity, the search is on for new lead-free compounds, such as PbTiO3-type perovskite or potassium sodium niobate (KNN)-based materials, as potential replacements for PZT.9−19 Several PbTiO3-type compounds with enhanced c/a ratios, such as PbVO3,9,10 BiCoO3,11 Bi2ZnTiO6,12 and BiFeO3 in thin film form13 have recently been found. PbVO3 has a c/a ratio of 1.23, much larger than that of PbTiO3 (1.06). The temperature dependence of the magnetic susceptibility measured on single crystals indicated a twodimensional antiferromagnetism originating from the ordering of dxy orbitals, which is thought to be related to the large tetragonal distortion.20 A tetragonal to cubic phase transition under pressure accompanied by a 9.4% volume collapse and drop in electrical resistivity was observed.9,21 BiCoO3 has an even larger distortion, with a c/a ratio of 1.27. Neutron © XXXX American Chemical Society

diffraction measurements indicated a C-type antiferromagnetic ordering of high-spin Co3+ magnetic moments.11 A pressureinduced phase transition accompanied by a 13% volume collapse and spin state transition was also observed.22 A monoclinic phase with a √2a × √2a × a unit cell, where a is the lattice parameter of a cubic perovskite and Cm space group, the same as in the low temperature phase of the MPB composition of PZT, was found in a solid solution between BiCoO3 and rhombohedral BiFeO3.23,24 Bi2ZnTiO6 is a B-site mixed double perovskite compound with a PbTiO3 structure and a large tetragonal distortion of c/a = 1.21.12 The highly insulating character of this compound, owing to the presence of only closed-shell ions in the B-site, makes it a good candidate for dielectric applications. Considering that the higher c/a ratio of PbVO3 relative to PbTiO3 is a result of the replacement of the Ti with a V ion, we thought that the tetragonal distortion might also be enhanced in Bi2ZnVO6. In our experiment, we synthesized a new PbTiO3type compound, Bi2ZnVO6, that had a larger distortion by using a high-pressure (HP) technique and investigated its crystal structure and magnetic and transport properties. We also analyzed the stability of the giant tetragonal phases of Biperovskites under pressure. Received: November 10, 2014 Revised: February 3, 2015

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DOI: 10.1021/cm504133e Chem. Mater. XXXX, XXX, XXX−XXX

Article

Chemistry of Materials

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EXPERIMENTAL SECTION

Polycrystalline samples of Bi2ZnVO6 were prepared from a mixture of Bi2O3, ZnO, V2O3 and V2O5 with 10% excess of Bi and Zn. The Bi2O3 powder was preheated in a box furnace at 673 K for 6 h. The mixture was carefully ground using an agate mortar in a glovebox and sealed into a gold capsule with a diameter of 3.6 mm and a height of 5 mm, and then it was treated at 9 GPa and 1373 K for 30 min in a cubicanvil type HP apparatus. Bi2ZnTiO6 as a reference was prepared at 8 GPa and 1473 K from a mixture of Bi2O3, ZnO and TiO2 in a stoichiometric ratio. BiCoO3 was prepared as previously reported.22 Synchrotron X-ray diffraction (SXRD) data for Bi2ZnVO6 under ambient conditions were collected with the large Debye−Scherrer camera installed on the BL02B2 beamline of SPring-8 (wavelength of 0.42000 Å). The diffraction data were analyzed with the Rietveld method using the RIETAN-FP program.25 Laboratory XRD data were collected at various temperatures with a D8 ADVANCE diffractometer (Bruker) with Cu Kα radiation, and the lattice parameters were refined with the Rietveld method using TOPAS software. High-resolution transmission electron microscope (HRTEM) images, Energy dispersive X-ray spectroscopy (EDX) and the selected-area electron diffraction (SAED) patterns were taken using a JEOL JEM-2100F microscope. The SXRD data for Bi2ZnVO6 and Bi2ZnTiO6 at HP were collected at the BL22XU beamline of SPring-8 using a diamond anvil cell (DAC) with helium as the pressure medium (wavelength of 0.49484 Å). The HP SXRD data of BiCoO3 were collected with the same system but the wavelength was 0.61990 Å. Thermal stability of Bi2ZnVO6 was examined using a Rigaku-TG8120 TG-DTA instrument. The sample was placed in a Pt crucible, heated to 1273 K at a rate of 2 K/min and cooled to room temperature at a rate of 5 K/min. The temperature dependence of the magnetic susceptibility of Bi2ZnVO6 was measured with a SQUID magnetometer (Quantum Design, MPMS XL) in an external magnetic field of 1000 Oe. The temperature dependence of the electrical resistivity of the materials was measured using the two-probe method. Dielectric measurements were performed at 0.1 V/mm using a Hewlett-Packard Precision LCR meter (HP 4284A). For the measurements, Au electrodes were deposited using DC sputtering method on sintered pellets of Bi2ZnVO6 and Ag wires were attached with Ag paste.

Figure 1. (a) Rietveld refinement of SXRD pattern of Bi2ZnVO6 at room temperature. Observed (+), calculated (line), and their difference (bottom line) profiles are shown. Bragg reflections are indicated by tick marks for Bi2ZnVO6 (top). The lower tick marks are for the impurity phase VO. (b) Crystal structure of Bi2ZnVO6. (c−e) SAED patterns of Bi2ZnVO6 viewed along the [001], [100], and [110] zone axes.

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deviations. All the occupation factors were fixed to unity in the final refinement. Our EDX analysis indicated the atomic mole ratio of Bi:Zn:V = 2:1.04:1.03, the same as the result of the Rietveld refinement in the experimental error. We tentatively assume that excess Bi and Zn reacted with the Au capsule during the high temperature treatment because these are volatile elements.27 This assertion is in accordance with our experimental result that the synthesis at higher temperature resulted in heavier reaction with gold and the presence of VO impurity. Table 1 lists the refined structural parameters with satisfactorily low R factors,25 and Table 2 lists the bond lengths. The bond valence sum (BVS)28 for the B site calculated for the refined bond distances and average bond valence parameters for Zn2+ and V4+ valences was +2.85. Considering the normal

RESULTS AND DISCUSSION Crystal Structure and Polarization of Bi2ZnVO6. As stated above, Bi2ZnVO6 was synthesized from starting oxides with 10% excess Bi and Zn. Our attempts to synthesize Bi2ZnVO6 from a stoichiometric composition resulted in the presence of VO impurity. We found the sample quality was quite sensitive to the synthesis pressure and temperature. For example, samples prepared at 8 GPa and 1373 K, 9 GPa and 1273 K, and 9 GPa and 1473 K contained large amounts of impurities even starting from 10% Bi and Zn excess composition. Furthermore, the gold capsule seriously reacted with the sample. Figure 1a shows the SXRD pattern of Bi2ZnVO6 and the results of the Rietveld fitting (the structure is illustrated in Figure 1b). It is known that the rock-salt type or layered ordering of the B-site cations results in either the √2a × √2a × 2a or 2a × 2a × 2a superstructure.26 The absence of either discrete supercell reflections or streaking in the SAED pattern along the [001], [100], and [110] zone axes (Figure 1c−e) associated with the cell doubling confirms that the Zn and V cations were randomly distributed in the B sites. Therefore, a tetragonal a × a × c unit cell was chosen. The atomic positions of Bi2ZnTiO6 were used in the initial structure model for the Rietveld refinement. Since the deviation of the cation ratio from 2:1:1 was suggested from the starting composition, the occupation factors of Bi, Zn, and V were refined, but these converged to 1:0.5:0.5 within the standard

Table 1. Crystallographic Parameters of Bi2ZnVO6 at Room Temperaturea site

Wyckoff position

x

y

z

Uiso(Å2)

g

Bi Zn V O1 O2

1a 1b 1b 1b 2c

0 0.5 0.5 0.5 0.5

0 0.5 0.5 0.5 0

0 0.5752(4) 0.5752 0.2167(0) 0.7352(2)

0.0301(5) 0.0111(9) 0.0111 0.0882(4) 0.0185(9)

1.0 0.5 0.5 1.0 1.0

a

Space group P4mm (No. 99), Z = 1, a = 3.7869(3) Å, c = 4.7660(7) Å, ρcalc = 7.6564 g/cm3, V = 68.34(9) Å3. R values (%): Rwp = 4.87; Rp = 3.30. Occupation factors of all sites are fixed to unity. B

DOI: 10.1021/cm504133e Chem. Mater. XXXX, XXX, XXX−XXX

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Chemistry of Materials

generate cracks and defects in the materials. We did not observe any contrast from the 180° domains. The large c/a ratio of PbTiO3-type compounds is mainly due to the large displacement of the O1 atom in the z direction away from the ideal (1/2, 1/2, 0) position. In the giant tetragonal compounds, PbVO3, BiCoO3, Bi2ZnTiO6, and Bi2ZnVO6, the large displacement makes the B−O coordination pyramidal rather than octahedral. Table 3 summarizes

Table 2. Selected Interatomic Distances of Bi2ZnVO6 at Room Temperaturea

a

bond

bond length (Å)

bond

bond length (Å)

Bi−O1(×4) Bi−O2(×4) Bi−O2(×4)

2.8700(4) 2.2755(2) 3.9828(8)

B−O1 B−O2(×4) B−O1

1.7086(4) 2.0412(6) 3.0574(3)

B represents Zn/V.

valences of Bi3+ and Zn2+, the valence state of Bi2ZnVO6 should be Bi3+2Zn2+V4+O6. The SXRD peaks of Bi2ZnVO6 were very broad, with the main peaks’ full width at half-maximum (FWHM) being 0.110°. Such peak broadening was also observed in Bi2ZnTiO6, and it was attributed to strained regions with locally suppressed polarization and tetragonality.29 The peak broadening in Bi2ZnTiO6 disappeared after annealing at high temperature (673 K) as the strain was released. On the other hand, the broad features of the SXRD peaks of Bi2ZnVO6 showed no significant change after annealing at 673 K for 8 h, suggesting that the broadening was not induced by the strained regions. To clarify the origin of the peak broadening, TEM observations were made. Figure 2a shows a typical bright-field TEM image

Table 3. Some Structure Parameters of PbTiO3-Type Perovskite Compounds compd

PbTiO3

PbVO3a

Bi2ZnTiO6a

BiCoO3a

Bi2ZnVO6

c/a δO1 ΔB (Å) PS (μC/cm2)

1.06 0.1118 0.32 59

1.23 0.2102 0.60 101

1.21 0.184 0.58 103

1.27 0.2034 0.73 103

1.26 0.2167 0.76 126

The structural parameters are from refs 9, 11, and12. δO1: Displacement of the O1 atom in the z direction from the ideal position (1/2, 1/2, 0). ΔB: The B site displacement from the oxygen square plane formed by O2. Ps: Spontaneous electrical ionic polarization as calculated with a point charge model at room temperature and ambient pressure (AP). a

selected structural parameters of PbTiO3-type compounds. The O1 displacement in Bi2ZnVO6 (0.2167) is the largest among them (PbTiO3 (0.1118), PbVO3 (0.2102), BiCoO3 (0.2034), and Bi2ZnTiO6 (0.1840)). Note also that the B-site displacement (ΔB) from the oxygen square plane formed by O2 of Bi2ZnVO6 is the largest. As a result, the two Zn(V)−O1 distances in Bi2ZnVO6 are significantly different, 1.7086(4) Å and 3.0574(3) Å (See Table 2), indicating the pyramidal MO5. The large distortion leads to a large electrical polarization. A point charge model calculation gave a spontaneous electrical ionic polarization (PS) of 126 μC/cm2, the largest among the known PbTiO3-type compounds, even larger than that of BiCoO3 with the largest c/a ratio. According to an empirical relation between TC and PS (in μC/cm2), i.e., TC = (0.303 ± 0.018)PS2,31 the TC of Bi2ZnVO6 is expected to be about 4800 K. In the case of BiFeO3 and BiCoO3, this equation gives about 5 times estimated values.22 The actual TC is probably about 1000 K. The high-TC prohibited us from observing the transition to the paraelectric phase on heating. Instead, we studied the stability of the giant tetragonal phase under pressure. Stability of Bi2ZnVO6 under Pressure. The TG-DTA data indicated that this compound decomposed into Bi3.85Zn0.45V1.7O10.475 and ZnO at 730 K without any structural phase transition. Figure 3a shows the temperature dependence of the lattice parameters. Both the a- and c-axis expanded while

Figure 2. (a) Typical bright-field TEM image of Bi2ZnVO6 taken by slightly tilting the sample from the [100] zone axis. The inset is the diffraction pattern obtained from the corresponding area. (b) Highresolution HRTEM image of the dotted region in a. The incident electron directions for the diffraction pattern and the HRTEM image are parallel to the [100] axis.

taken by slightly tilting the sample from the [100] zone axis. The inset is the electron diffraction pattern obtained from the corresponding area. Figure 2b is a magnified view (HRTEM image) of the dotted region of Figure 2a. The incident electron directions for both the diffraction pattern and the HRTEM image are parallel to the [100] axis. There were 90° domains with a {011} twin plane. The angle between the c axes on either side of the wall was 102.6°, which deviated from 90° due to geometrical requirements to form coherent twin interfaces in tetragonal Bi2ZnVO6. The value 102.6° corresponds to a tetragonality of c/a = 1.25, in good agreement with the ratio determined from the XRD data (1.26). Interestingly, the widths of the domains were very small (from 5 to 20 nm). The average crystallite size estimated using the Scherrer equation30 on the FWHM of the (011) peak of the SXRD data, 19.5 nm, was the same order as the width of the domains. The deviation may be attributed to the stripe shape of the domains because the Scherrer equation assumes isotropic particles. Thus, we believe that the broad features of the SXRD peaks of Bi2ZnVO6 were mainly induced by the presence of domains. However, we cannot exclude the possibility of stress as that in PbTiO3 because the large tetragonal distortion (c/a = 1.26) can

Figure 3. (a) Temperature dependence of lattice parameters of Bi2ZnVO6 between 120 and 500 K. (b) Temperature dependence of the c/a ratio. C

DOI: 10.1021/cm504133e Chem. Mater. XXXX, XXX, XXX−XXX

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Chemistry of Materials the c/a ratio slightly decreased (Figure 3b) with increasing temperature from 100 to 570 K. This behavior suggests that the electrical ionic polarization decreased on heating, as has been observed in BiCoO3 and Bi2ZnTiO6.11,12 We studied the HP behavior, as there was no transition to the paraelectric phase under heating. Figure 4a plots the

(1.3%) at the transition pressure. On the other hand, the volume collapse of BiCoO3 is pronounced, as large as 13%.22 This is because the compressibility of the ambient pressure (AP) phase of BiCoO3 is almost the same as that of the HP phase, whereas the AP phases of Bi2ZnVO6 and Bi2ZnTiO6 are more compressible than the HP phases. The unit cell volumes (V) of the two phases as a function of pressure (P) were fitted to the second order Birch−Murnaghan equation of state (EOS), P = (3/2)K0[(V0/V)7/3 − (V0/V)5/3], where K0 is the bulk modulus and V0 is the volume at ambient pressure.39 The fitting results give a K0 of 48.0 and 20.4 GPa for the AP phase for Bi2ZnVO6 and Bi2ZnTiO6, respectively. The K0 value for the BiCoO3 AP phase is 74.0 GPa, confirming that this compound is stiffer than Bi2ZnVO6 and Bi2ZnTiO6. According to the previous report,22 the large volume collapse of BiCoO3 was mainly induced by shrinkage of the c axis. The c/a ratio of BiCoO3 in the AP phase was almost independent of pressure, as shown in Figure 4c, whereas the c/a ratios of Bi2ZnVO6 and Bi2ZnTiO6 dramatically decreased with increasing pressure and were as small as 1.1 at the transition pressure. The structural transition in BiCoO3 is accompanied by a high-spin to low-spin state transition. Since the spin state is determined by competition between crystal field splitting and Hund’s coupling, and the former coupling is sensitive to the c/a ratio, the c/a ratio of the BiCoO3 giant tetragonal phase is almost constant so long as the high-spin state is preserved. On the other hand, such an electronic state change is absent from Bi2ZnVO6 and Bi2ZnTiO6, resulting in a variable c/a ratio and anisotropic compressions. Magnetic, Transport, and Dielectric Properties of Bi2ZnVO6. The temperature dependence of the magnetic susceptibility showed no trace of a magnetic transition in the measured temperature range of 5−300 K. Figure 5a shows field cooling (FC) data measured from 300 to 5 K in a magnetic field of 1000 Oe. This paramagnetism may be attributed to the random distribution of nonmagnetic Zn2+ and magnetic V4+ ions. The data in the high temperature region between 150 and

Figure 4. (a) SXRD patterns of Bi2ZnVO6 collected at various pressures and at room temperature. Ticks marked at the bottom of the patterns at 4.70 and 10.40 GPa denote the positions of the Bragg reflections. (b) Pressure dependence of the unit cell volume per formula unit for Bi2ZnVO6, Bi2ZnTiO6, and BiCoO3. Solid and open symbols represent the ambient and HP phases, respectively. (c) Pressure dependence of the c/a ratio of the tetragonal phases of Bi2ZnVO6, Bi2ZnTiO6, and BiCoO3.

pressure dependence of the SXRD patterns at room temperature. A structural transition from the tetragonal polar PbTiO3 type to the GdFeO3 type of paraelectric orthorhombic structures was clearly observed at around 6 GPa. The presence of both phases indicates the first order character of the transition. No further structural transition was observed up to 11.30 GPa. This phase transition is similar to those of other BiMO3 (M = Sc, Cr, Fe, Mn, Ni) compounds, whose structures change into the GdFeO3-type orthorhombic one under pressure.32−35 Among A2+Ti4+O3 perovskites, a PbTiO3 type structure is obtained when the factor (t) is larger than 1.36 Because of large Bi3+ and small M3+, t is ∼0.95 for Bi3+M3+O3 (0.948 for Bi2ZnVO6)37,38 and GdFeO3-type distortion is expected. The stereochemical activity of Bi3+ stabilizes the tetragonal distortion, and the GdFeO3-type structure is observed as a HP paraelectric phase. Because of the limited number of particles in the small sample space of the DAC, the measured intensity ratio was not reliable, prohibiting us from refining the structural parameters with the Rietveld method. Figure 4b plots the pressure dependence of the unit cell volume of Bi2ZnVO6 per formula unit, together with those of BiCoO3 and Bi2ZnTiO6 for comparison (SXRD patterns and lattice parameters are in Figures S1 and S2). The unit cell volume of Bi2ZnVO6 decreased linearly with increasing pressure, and there was a 2.4% volume collapse at the phase transition pressure (6.01 GPa). The iso-structural compound of Bi2ZnTiO6 also showed a transition to the GdFeO3-type orthorhombic phase at 1.09 GPa (Figure S1a), but with a much smaller volume collapse

Figure 5. (a) Temperature dependence of the magnetic susceptibility of Bi2ZnVO6 and the fitting results to the Curie−Weiss law. (b) Temperature dependence of the resistivity of Bi2ZnVO6. The inset shows the Arrhenius fit. (c) Dielectric permittivity and (d) dielectric loss of Bi2ZnVO6 as a function of temperature for selected frequencies. D

DOI: 10.1021/cm504133e Chem. Mater. XXXX, XXX, XXX−XXX

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Chemistry of Materials 300 K were fitted to the Curie−Weiss law with a temperatureindependent term, χ = χ0 + C/(T − θ), where χ0 is the temperature independent susceptibility, C is the Curie constant, and θ is the Weiss temperature. The data were normalized to the starting composition of Bi2.2Zn1.1VO6. The fitting result (the blue line in Figure 5a) gives χ0 = −4.62 × 10−4 emu/mol, C = 0.274 emu·K/mol, and θ = −89 K, indicating that the effective magnetic moment is 1.48 μB, which is a little smaller than the 1.73μB expected from V4+. The deviation may be induced by the secondary phase VO. The temperature dependence of the resistivity of a polycrystalline sample (Figure 5b) exhibited semiconducting behavior (dρ/dT < 0). The data could only be attained in the limited temperature range between 340 and 370 K because the resistance at low temperature was out of the range of our set up. The Arrhenius conduction model40 [ln ρ(T) ∞ T−1] fitted the ρ(T) values well and indicated an activation gap of about 0.43 eV (see the inset of Figure 5b). Considering the dark gray color of the sample, the band gap is underestimated, most probably owing to the presence of the semiconducting secondary phase, VO.41 Figure 5c and d shows the temperature dependence of dielectric permittivity and loss, respectively. The increase in relative permittivity on heating may suggest that the system approached the ferroelectric transition at higher temperature. The magnitude of the dielectric loss was higher than that of Bi2ZnTiO612 in accordance with the resistivity data.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank Profs. Mitsuru Itoh and Takao Sasagawa of the Materials and Structures Laboratory, Tokyo Institute of Technology for their help in the resistivity, dielectric properties, and magnetic measurements. This work was partially supported by Grants-in-Aid for Young Scientists (B) (Grants 26820291 and 26800180) and Creative Scientific Research (Grant 26106507) from the Japan Society for the Promotion of Science (JSPS). The synchrotron-radiation experiments were performed at SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (Grants 2011B3782, 2013A1652, 2013B3615, 2014A3615, and 2014A3784) and under the Shared User Program of JAEA Facilities (Grants 2011B-E03 and 2014A-E21) with the approval of the Nanotechnology Platform project supported by the Ministry of Education, Culture, Sports, Science and Technology (Grant A-14-AE-0015).

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CONCLUSION In conclusion, we synthesized a new PbTiO3-type B-site random double perovskite, Bi2ZnVO6, with a giant tetragonal distortion of c/a = 1.26 and a spontaneous electrical ionic polarization of 126 μC/cm2, the largest among the PbTiO3type compounds reported so far. The temperature dependence of the c/a ratio decreased with increasing temperature, and there was no structural transition below the decomposition temperature of 730 K. A structural transition from polar to paraelectric orthorhombic was observed at 6.01 GPa, and it was accompanied by a 2.4% volume collapse. The pressure dependence of the lattice parameters and the c/a ratio indicated anisotropic compression. The bulk modulus as determined by the fitting to the second-order Birch− Murnaghan equation was K0 = 48.0 GPa. Paramagnetism due to the random distribution of nonmagnetic Zn2+ and magnetic V4+ ions and semiconductivity with an activation energy of 0.43 eV were observed. This polar compound with a large tetragonal distortion is a promising candidate as the end number of high performance piezoelectric solid solution with a morphotropic phase boundary.

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ASSOCIATED CONTENT

S Supporting Information *

Figures showing SXRD patterns of BiCoO3 and Bi2ZnVO6 collected at various pressures and pressure dependence of lattice parameters of Bi2ZnTiO6, Bi2ZnVO6, and BiCoO3 tetragonal phases. This material is available free of charge via the Internet at http://pubs.acs.org.

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REFERENCES

AUTHOR INFORMATION

Corresponding Authors

*(M.A.) E-mail: [email protected]. *(R.Y.) E-mail: [email protected]. E

DOI: 10.1021/cm504133e Chem. Mater. XXXX, XXX, XXX−XXX

Article

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DOI: 10.1021/cm504133e Chem. Mater. XXXX, XXX, XXX−XXX