Study of phase transition properties in rochelle salt crystal

Abstract

The extra spin-lattice interactions terms, external electric field term, direct spin-spin interaction term and fourth-order phonon anharmonic terms have been added to two-sublattice pseudo-spin lattice couples mode(PLCM) model for Rochelle salt crystal. By applying the double-time thermal Green function method and using the modified model, theoretically, expressions for the shift, width, soft mode frequency, dielectric constant and loss tangent have been derived. By fitting model parameters values, temperature variations of the above quantities have been calculated for Rochelle salt crystal. We compare theoretical variations of soft mode frequency for Rochelle salt crystal, by getting correlated values of soft mode frequency from experimental data of dielectric constant. We compare our theoretical values for dielectric constant and loss tangent for Rochelle salt with the experimental result of Sandy and Jones [Phys Rev, 168(2), 481-493 (1968)]. Our theoretical results well agree with experimental data of others for Rochelle salt. Present expressions will also be useful for other similar crystals like sodium ammonium tartrate tetrahydrate (NaNH₄C₄H₄O₆.4H₂O) crystal, lithium ammonium tartrate monohydrate (LiNH₄C₄H₄O₆.H₂O) crystal and lithium thallium tartrate monohydrate (LiTlC₄H₄O₆.H₂O) crystal etc.