TY - JOUR

T1 - Phase Transformations and Thermal Expansion of α- And β-BiTaO4 and the High-Temperature Modification γ-BiTaO4

AU - Zhuk, Nadezhda A.

AU - Krzhizhanovskaya, Maria G.

AU - Belyy, Vladimir A.

AU - Kharton, Vladislav V.

AU - Chichineva, Alena I.

PY - 2020/7/14

Y1 - 2020/7/14

N2 - Thermal analysis and X-ray phase analysis under high temperature have defined the order of the BiTaO4 phase transformations in the range of temperature from 25 to 1200 °C: α-BiTaO4 → γ-BiTaO4 → β-BiTaO4 and β-BiTaO4→ γ-BiTaO4 → β-BiTaO4; the new high-temperature phase of bismuth orthotantalate is γ-BiTaO4. It was shown that the transition α-BiTaO4 → β-BiTaO4 is irreversible, in contrast to BiNbO4. The crystal structure of the new bismuth orthotantalate high-temperature modification (γ-BiTaO4) was studied by X-ray powder diffraction. The possible space group of the high-temperature orthorhombic phase was determined as Cmcm, and the parameters of the unit cell were calculated at 900 °C: a = 3.92455(4), b = 15.06243(16), c = 5.63483(6) Å, and V = 333.093(6) Å3. As an alternative, the space group of γ-BiTaO4 was determined as P21/c, and the following unit cell parameters were calculated: a = 7.78151(10), b = 5.63466(6), c = 7.84843(7) Å, β = 104.5858(17)°, and V = 333.033(7) Å3. The method of HTPXRD was used to obtain thermal expansion coefficients (TECs) and to study the thermal deformations of the α, β, and γmodifications of BiTaO4. The average volumetric TECs of all modifications studied had the range of 18.4-33.6 × 10-6 °C-1. The highest anisotropy of thermal expansion was the characteristic of the triclinic phase, β-BiTaO4, whereas α-BiTaO4 had minimal anisotropy and TEC indicating the highest stability of this modification.

AB - Thermal analysis and X-ray phase analysis under high temperature have defined the order of the BiTaO4 phase transformations in the range of temperature from 25 to 1200 °C: α-BiTaO4 → γ-BiTaO4 → β-BiTaO4 and β-BiTaO4→ γ-BiTaO4 → β-BiTaO4; the new high-temperature phase of bismuth orthotantalate is γ-BiTaO4. It was shown that the transition α-BiTaO4 → β-BiTaO4 is irreversible, in contrast to BiNbO4. The crystal structure of the new bismuth orthotantalate high-temperature modification (γ-BiTaO4) was studied by X-ray powder diffraction. The possible space group of the high-temperature orthorhombic phase was determined as Cmcm, and the parameters of the unit cell were calculated at 900 °C: a = 3.92455(4), b = 15.06243(16), c = 5.63483(6) Å, and V = 333.093(6) Å3. As an alternative, the space group of γ-BiTaO4 was determined as P21/c, and the following unit cell parameters were calculated: a = 7.78151(10), b = 5.63466(6), c = 7.84843(7) Å, β = 104.5858(17)°, and V = 333.033(7) Å3. The method of HTPXRD was used to obtain thermal expansion coefficients (TECs) and to study the thermal deformations of the α, β, and γmodifications of BiTaO4. The average volumetric TECs of all modifications studied had the range of 18.4-33.6 × 10-6 °C-1. The highest anisotropy of thermal expansion was the characteristic of the triclinic phase, β-BiTaO4, whereas α-BiTaO4 had minimal anisotropy and TEC indicating the highest stability of this modification.

UR - http://www.scopus.com/inward/record.url?scp=85087135665&partnerID=8YFLogxK

U2 - 10.1021/acs.chemmater.0c00010

DO - 10.1021/acs.chemmater.0c00010

M3 - Article

AN - SCOPUS:85087135665

VL - 32

SP - 5493

EP - 5501

JO - Chemistry of Materials

JF - Chemistry of Materials

SN - 0897-4756

IS - 13

ER -