A careful experimental investigation of the ferroelectric-paraelectric transition in uniaxial ferroelectric telluric acid ammonium phosphate induced by pressure and by temperature in the vicinity of the phase transition has been carried out. Dielectric-constant and hysteresis-loop data allow the determination of the combined equation of state as a function of both temperature and pressure, relating accurately polarization, field, pressure, and temperature in the neighborhood of the transition.

• Received 4 August 1995

DOI:https://doi.org/10.1103/PhysRevB.53.R2903