Phase Transition Dielectric Properties in Order-disorder Antiferroelectric NH4(H2PO4) (ADP) Crystal

A modified four sublattice pseudospin lattice coupled model Hamiltonian by adding extra spin-lattice interaction, direct spin-spin interaction has been used to study dielectric properties for ammonium dihydrogen phosphate (ADP) crystal. Using the double-time temperature-dependent Green’s function method, the expressions for soft mode frequency, dielectric permittivity and loss tangent have been derived. By fitting the model values of various physical parameters, the thermal variations of the above quantities are calculated and compared with the experimental results. Our theoretical obtained results are in good agreement with experimental data.