V. D. Fokina

Effect of Cationic Substitution on Ferroelectric and Ferroelastic Phase Transitions in Oxyfluorides A2A′WO3F3 (A, A′: K, NH4, Cs)

Thermal properties and structure of initial and distorted phases of crystals K 2 KWO 3 F 3 , (NH 4 ) 2 KWO 3 F 3 , (NH 4 ) 3 WO 3 F 3 , Cs 2 NH 4 WO 3 F 3 and Cs 2 KWO 3 F 3 were studied to reveal the effect of cationic substitution on disordering and stability of cubic Fm3m phase. It was found that the nature of phase transitions depends on the shape of cation in 8c position.

Mechanism and nature of phase transitions in the (NH4)3MoO3F3 oxyfluoride

AbstractThe temperature dependences of the heat capacity, the unit cell parameter, and the permittivity for the (NH4)3MoO3F3 cryolite (space group Fm

Heat capacity, p-T phase diagram, and structure of Rb2KTiOF5

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Thermophysical studies of the phase transitions in (NH4)3NbOF6 crystals

m) are investigated. It is revealed that the compound undergoes ferroelectric and ferroelastic structural phase transitions at temperatures of 297 and 205 K, respectively. The mechanism of structural distortions is discussed in terms of the entropy parameters, pressure-temperature phase diagrams, and electron density maps for critical atoms. An analysis is made of the influence of the cation size and shape on the phase transitions in oxyfluorides of the general formula A2A′MO3 (A,A′ = NH4, K; M = Mo, W).

Mechanism of phase transitions in the (NH4)2WO2F4 ferroelastic

The heat capacity and unit cell parameters of the (NH4)3WO3F3 and (NH4)3TiOF5 perovskite-like oxyfluorides were measured in the temperature interval from 80 to 300 K; the existence of two and one phase transitions in these compounds, respectively, was demonstrated, and their thermodynamic parameters were determined. The effect of a hydrostatic pressure of up to 0.5 GPa on the phase transition temperatures was studied. Triple points and high-pressure phases were found in the T vs. p diagrams. An analysis of entropy changes suggests that all the structural transformations revealed are associated with the ordering of structural blocks.

Structural phase transition in elpasolite-like (NH4)2KWO3F3

AbstractElpasolite Rb2KTiOF5 (space group, Fm

A Raman scattering study of the phase transition in the (NH4)3WO3F3 oxyfluoride

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