X-ray study on thermal expansion of ferroelectric KH2PO4

Abstract

The lattice parameters of KH2PO4 at various temperatures between 23.4 and —169.3 °C have been measured by using an accurate X-ray method recently developed by the authors. Specifical emphasis was laid on their temperature dependence near the ferroelectric Curie point. Small but distinct thermal hysteresis was found to occur at the onset of the para-electric-ferroelectric phase transformation. The results of temperature variation of the lattice parameters are in fairly good agreement with those of other authors except in the vicinity of the Curie point. It is noticeable that a pure shear x in a plane perpendicular to the ferroelectric axis, which directly reflects the spontaneous polarization, begins to decrease more rapidly than Ps as temperature approaches the Curie point.