Phase transitions, crystal growth

Barocaloric properties of ceramic (NH$_4$)$_3$H(SO$_4$)$_2$

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

a</sup> Kirensky Institute of Physics, Federal Research Center KSC SB, Russian Academy of Sciences, Krasnoyarsk, Russia
^b Institute of Engineering Physics and Radioelectronics, Siberian Federal University, Krasnoyarsk, Russia
^c Krasnoyarsk State Medical University named after Professor V. F. Voyno-Yasenetsky, Krasnoyarsk, Russia
^d Institute of Engineering Systems and Energy, Krasnoyarsk State Agrarian University, Krasnoyarsk, Russia

Abstract: An experimental study of the heat capacity, thermal expansion, and the effect of hydrostatic pressure on the permittivity of ceramics (NH$_4$)$_3$H(SO$_4$)$_2$ was carried out in the region of low-temperature phase transitions $A2/a\leftrightarrow(P2/n)_1\leftrightarrow(P2/n)_2\leftrightarrow P-1$. The main thermodynamic characteristics were determined: entropy, deformation and baric coefficients associated with successive distortions of the crystal lattice. The position of the boundaries between phases $(P2/n)_1$, $(P2/n)_2$ and $P-1$ in the temperature – pressure diagram was clarified. Based on the analysis of the $S(T,p)$ functions, the values and character of the temperature and baric behavior of the parameters of extensive and intensive barocaloric effects are determined. The absence of temperature hysteresis and a wide range of anomalous heat capacity during the $A2/a\leftrightarrow P2/n$ transition ensure high reproducibility of thermo- and barocycling processes and significant relative cooling capacity of (NH$_4$)$_3$H(SO$_4$)$_2$. Keywords: phase transitions, heat capacity, thermal expansion, pressure, barocaloric effect.

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

DOI: 10.61011/FTT.2024.10.59087.244

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