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Effect of Deuteration on Phase Transitions in Vanadium Dioxotetrafluoride

The crystals of (ND 4 ) 3 VO 2 F 4 with a high degree of deuteration (~87%) have been grown and a significant (~1.5%) increase in the unit cell volume has been detected. The decrease in the chemical pressure leads to a change in the sequence of phase transitions due to wedging-out of one of the rhom...

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Bibliographic Details
Published in:Physics of the solid state 2019-02, Vol.61 (2), p.192-200
Main Authors: Bogdanov, E. V., Pogoreltsev, E. I., Gorev, M. V., Molokeev, M. S., Flerov, I. N.
Format: Article
Language:English
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Summary:The crystals of (ND 4 ) 3 VO 2 F 4 with a high degree of deuteration (~87%) have been grown and a significant (~1.5%) increase in the unit cell volume has been detected. The decrease in the chemical pressure leads to a change in the sequence of phase transitions due to wedging-out of one of the rhombic phases observed in (NH 4 ) 3 VO 2 F 4 . The thermal physical studies have been carried out and the entropies, deformations, and pressure coefficients related to structural transformations have been determined. The T – p phase diagram has been built and the pressure and temperature boundaries of crystal phase stability have been determined. The dielectric studies demonstrate a nonferroelectric nature of the phase transitions in (ND 4 ) 3 VO 2 F 4 . The experimental and model entropies are compared. Based on the decrease in the entropy as a result of deuteration, a hypothesis on significant but not limited anharmonism of vibrations of ammonia tetrahedral corresponding to the disordering is proposed.
ISSN:1063-7834
1090-6460
DOI:10.1134/S1063783419020082