Abstract
The article discusses the use of KDP ferroelectric crystals (phosphates and arsenates of potassium, rubidium, cesium) and their deuterated analogues in various industries, including the creation of electro-optical devices and as hydrogen sorbents. The paper describes the physical properties of KDP crystals, changes in their properties near the phase transition temperature, as well as methods for obtaining KDP nanocrystals and their application in biomedicine. The paper also states that the phase transition in KDP crystals occurs near room temperature and manifests itself in a change in their physical properties, such as dielectric constant, optical properties, and heat capacity. In addition, approaching the phase transition temperature causes a change in the crystal lattice parameters, which can lead to the appearance of anomalous effects. The structure of the unit cell of potassium dihydrogen phosphate (KH2PO4) is considered. The plots of the temperature dependence of the order parameter of spontaneous polarization and the plots of the temperature dependence of the configurational heat capacity of the crystal in the phase transition region are calculated, and the plots of the temperature of the inverse and direct dielectric susceptibility are calculated. Graphs of the order parameter, which characterizes the degree of spontaneous polarization for different temperatures, depending on the strength of the external electric field, are also calculated.