Dielectric properties of compressed Rochelle-salt powders

The dielectric constant has been measured on compressed Rochelle-salt powders of varying particle sizes under different conditions of humidity. The measurements were made at 100 kHz in a temperature range from −60 to +45 °C which covers the ferroelectric and both the paraelectric regions. Under normal conditions of temperature and humidity, both the para–ferro–paraelectric phase transitions in all the compressed powders up to 20 μm particle size were observed. The ferroelectricity in these powders were confirmed by observing the hysteresis loops. It was noticed that the lower transition temperature increased with decreasing particle size while the upper transition temperature remained almost unaffected, thus decreasing the ferroelectric temperature range with decreasing particle size. There was no change in the dielectric constant with particle size indicating that the surface layers as well as the depolarization field in the case of Rochelle salt have no significant effect up to 20 μm particle size. The experimental values of the dielectric constant were in reasonably good agreement with the values calculated by modified Bruggeman's formula.