Structures and phase transitions in the ordered double perovskites Ba₂Bi^IIIBi^VO₆ and Ba₂Bi^IIISb^VO₆

Abstract

High-resolution neutron powder diffraction has been used to investigate the structures and phase transitions in the double perovskites Ba(2)Bi(3+)Bi(5+)O(6) (dibarium dibismuth hexaoxide) and Ba(2)BiSbO(6) (dibarium bismuth antimony hexaoxide) in the temperature ranges 4.2-973 and 4.2-625 K, respectively. The charge-ordered bismuthate adopts four structures in the temperature range - monoclinic in P2(1)/n, monoclinic in I2/m, rhombohedral in R3, and finally cubic in Fm3m. The low-temperature monoclinic structure has been determined for the first time. The transitions from P2(1)/n to I2/m, at 132 K, and R3 to Fm3m, at 820 K, are tricritical in nature; the transition from I2/m to R3 at ca 430 K is discontinuous. The behaviour of Ba(2)BiSbO(6) is very similar, except that the transition temperatures are lower - 250 K for I2/m to R3 and 515 K for R3 to Fm3m - and the low-temperature structure is not formed at all. The R3 to Fm3m transition in this compound is closer to second order in nature, although there is evidence for some contribution from higher-order terms.

Temperature‐dependent Raman spectra of Ba2BiSbO6 ceramics

“…[6]. The atomic positions, potentials and the effective charges were optimized with respect to minimal energy.…”

Relaxations in Ba2BiSbO6 double complex perovskite ceramics

“…These discontinuous changes reflect the structural phase transitions that the Ba 2 BiSbO 6 compound undergoes near 242°C. 30 There are discontinuities to the same temperature in the A and B estimated parameters as shown in Fig. 8.…”

“…Each compound shows at least three phases, the aristotype at high temperatures, a rhombohedral R3 phase at intermediate temperatures, and a monoclinic I2 / m phase at low temperatures. [30][31][32] BaBiO 3 shows these same three phases but the phase transitions occur at high temperatures. At room temperature BaBiO 3 is monoclinic with symmetry I2 / m and at low temperatures it is monoclinic with P2 1 / n symmetry.…”

“…[20][21][22][23][24][25][26] Since that was confirmed, the Bi 4+ disproportionation [27][28][29] in Bi 3+ and Bi 5+ ions has emerged a very intense interest in related compounds where Bi 5+ is substituted for another pentavalent ion such as Sb 5+ and Ta 5+ . [30][31][32][33][34][35] This family of compounds shows a rich phase diagram with temperature changes. Each compound shows at least three phases, the aristotype at high temperatures, a rhombohedral R3 phase at intermediate temperatures, and a monoclinic I2 / m phase at low temperatures.…”

“…At room temperature BaBiO 3 is monoclinic with symmetry I2 / m and at low temperatures it is monoclinic with P2 1 / n symmetry. 30 The phase 36 and giant dielectric constant. 37 This work shows for the first time the use of impedance spectroscopy to characterize the temperature dependence of electrical properties of Ba 2 BiSbO 6 ceramic samples.…”