Measurement of Thermal Expansion and Spontaneous Strain of Rochelle Salt

The thermal dilatations l j ( j =1, 2, 3) of Rochelle salt were carefully measured in a temperature range -40°C to +40°C by means of the air-capacitor method. The coefficients of linear thermal expansion exhibit a step-like behavior at both Curie points and their amplitudes agree fairly well with those estimated previously by the thermoelastic effect. The step in volume thermal expansion shows a positive sign at both Curie points. The spontaneous strains were separated from the l j by the method of least squares. The electrostrictive constants Q 1 j and Q 1 h (for volume) were obtained and it was found that the Q 13 shows an opposite sign to that given by Mason and a considerable temperature dependence which makes the sign of Q 1 h change in the ferroelectric region.