Phase transitions

Thermophysical properties and barocaloric effect in ceramic ferroelectric NH$_4$HSeO$_4$

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

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

Abstract: The heat capacity, thermal expansion and hydrostatic pressure susceptibility of NH$_4$HSeO$_4$ ceramic samples have been investigated. The main parameters of the low temperature transitions between the para/pyroelectric $(T_1)$ $\leftrightarrow$ incommensurate $(T_2)$ $\leftrightarrow$ ferroelectric $(T_3)$ $\leftrightarrow$ para/pyroelectric phases were determined. The phase $T$–$p$ diagram was refined and the baric coefficient d$T_3$/d$p$ was determined. The volumetric strain behaviour and the results of direct measurements of $T_3(p)$ allowed us to establish the nature of the pressure effect on the stability of the ferroelectric phase. The extensive and intensive barocaloric effects were determined taking into account lattice thermal expansion.

Keywords: phase transitions, ferroelectrics, heat capacity, thermal expansion, pressure, barocaloric effect.

Received: 28.08.2023
Revised: 28.08.2023
Accepted: 01.09.2023

DOI: 10.61011/FTT.2023.10.56334.190

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