X-Ray Study on Thermal Expansion of Ferroeleetrie KH2PO4

The lattice parameters of KH2PO4 at various temperatures between 23.4 and 169.3 degrees 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 paraelectric-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 42 in a plane perpendicular to the ferroelectric axis, which directly reflects the spontaneous polarization, begins to decrease more rapidly than P-s as temperature approaches the Curie point.