Thermal properties

Effect of deuteration on phase transitions in (NH$_4$)$_3$VOF$_5$

E. V. Bogdanov^ab, V. S. Bondarev^ac, M. V. Gorev^ac, M. S. Molokeev^ac, I. N. Flerov<sup>ac

a</sup> L. V. Kirensky Institute of Physics, Siberian Branch of the Russian Academy of Sciences, Krasnoyarsk, Russia
^b Krasnoyarsk State Agricultural University, Krasnoyarsk, Russia
^c Institute of Engineering Physics and Radioelectronics, Siberian Federal University, Krasnoyarsk, Russia

Abstract: The (ND$_4$)$_3$VOF$_5$ crystal was grown with a high degree of deuteration ($D\approx$ 92%). Structural and thermophysical studies have been carried out, the parameters of phase transitions have been determined. It was found that the deuteration of the ammonium cation in (NH$_4$)$_3$VOF$_5$ led to a change in the chemical pressure, which was accompanied by an increase in the unit cell volume and an increase in the phase transition temperatures. The baric coefficients $dT_i/dp$ were determined and the phase $T$–$p$ diagram (ND$_4$)$_3$VOF$_5$ was constructed. A decrease in the temperature stability of the initial cubic phase $Fm\bar{3}m$ in (ND$_4$)$_3$VOF$_5$, as well as a wedging out of the intermediate monoclinic phase at a lower pressure as compared to (NH$_4$)$_3$VOF$_5$, was found.

Keywords: oxyfluorides, phase transitions, heat capacity, thermal expansion, pressure.

Received: 11.11.2021
Revised: 11.11.2021
Accepted: 13.11.2021

DOI: 10.21883/FTT.2022.03.52101.237

Bibliographic databases:

•