Effect of Electric Field, Hydrostatic, and Uniaxial Pressures on Physical Properties of NH ₄ HSO ₄ Ferroelectric Within the Framework of a Pseudospi

The static longitudinal dielectric, elastic, and thermal characteristics of the NH ₄ HSO ₄ crystal under the influence of a longitudinal electric field, as well as hydrostatic and uniaxial pressures, were calculated using a two‐sublattice pseudospin model of this ferroelectric. A linear dependence of the upper and lower Curie temperatures on the applied pressures has been demonstrated, as well as a linearly decreasing dependence of the lower Curie temperature on the electric field. The electrocaloric, barocaloric, and piezocaloric effects in this crystal have been investigated. The model predicts a negative electrocaloric temperature change near the lower Curie temperature, which can exceed 5 K.