Dielectric properties of quasi-one dimensional PbHPO₄ crystal in presence of external electric field

The third and fourth order phonon anharmonic interactions external electric field terms are added in the two-sublattice pseudospin model for PbHPO₄ crystal. By using double time thermal Green's function method modified model, theoretical expressions for soft mode frequency, dielectric constant, shift, width and tangent loss are evaluated for PbHPO₄ crystal. Temperature and field variations of soft mode frequency, dielectric constant and loss tangent are calculated numerically. Present theoretical results agree with experimental result of Smutney and Fousek for dielectric constant of PbHPO₄.