Temperature dependence of soft mode frequency, dielectric constant and loss tangent in potassium dihydrogen arsenate and deuterated potassium dihydrogen arsenate crystals

Abstract

The third and fourth order phonon anharmonic interactions terms and four spin coupling terms have been added in the pseudospin phonon coupled mode (PLCM) model for potassium dihydrogen arsenate (KDA) crystal. By using double-time thermal Green’s function method, expressions for soft mode frequency, dielectric constant and loss tangent have been obtained for KDA (KH₂AsO₄) crystal. Fitting model values in the theoretical expressions, the temperature dependence of ferroelectric soft mode frequency, dielectric constant and loss tangent have been calculated for KDA and deuterated KDA (DKDA) crystals. Theoretical results have been compared with experimental data of Kaminow, which show a good agreement.