CXXIII. The dielectric properties of barium titanate single crystals in the region of their upper transition temperature

Abstract

Abstract Measurements have been made of the ferroelectric hysteresis and dielectric constant of small single crystals of barium titanate from 20°c to 150°c. In untwinned crystals, free from external constraint the results clearly indicate that the ferroelectric transition occurring in the region of 120°c is a thermodynamically first order transition. Over a small range of temperature above the zero field transition electric hysteresis is reintroduced by the application of a sufficient electric field. The forms of the hysteresis figures in this temperature range are qualitatively explained in terms of Devonshire's treatment of the ferroelectrie effects. In twinned crystals, optical and electrical measurements show that it is not possible to fix accurately a transition temperature for the whole specimen, as different regions transform at different temperature. I t is suggested that the behaviour of these specimens may be due to imperfections in the crystal lattice, which give rise to local stresses in the region of the transition.