Dielectric properties of ferroelectric methylammonium aluminium sulphate alum (MASD) crystal

By considering two sublattice pseudospin lattice coupled mode model Hamiltonian has been modified to include the extra spin–lattice interactions, the direct spin–spin coupling interaction, an applied electric field and the phonon anharmonic interactions for MASD alum. By using double-time thermal-dependent Green function method and modified Hamiltonian formulation, the expressions for soft mode frequency, dielectric constant and dielectric tangent loss properties have been derived and evaluated. Fitting the model values of various physical parameters in theoretical obtained expressions, the thermal variations of the above quantities have been calculated. Theoretical results compare well with experimental data of others on MASD alum. •First, study and modify two sublattice pseudospin lattice coupled mode model Hamiltonian for ferroelectric methylammonium aluminum sulphate alum crystal•We obtained the response function using Green’s function theory and model Hamiltonian.•Using a symmetric decoupling scheme in the response function solved the higher order Green’s functions.•Using Green’s function and calculations, we obtained the dielectric and ferroelectric properties of methylammonium aluminum sulphate alum crystal.•Ferroelectric materials have diverse uses that permit numerous applications, ranging from piezoelectric sensing and dielectric energy storage to electrocaloric solid state cooling, which have attracted extensive research and development interests. The ferroelectric materials play a fundamental role in various modern electronic devices, such as sensors, transducers and piezoelectric actuators, while relaxor ferroelectrics and anti-ferroelectrics have great significance for high-power and pulse power dielectric energy storage.