FERROELECTRICITY IN CALCIUM TARTRATE SINGLE-CRYSTALS GROWN BY GEL TECHNIQUE

Single crystals of calcium tartrate have been grown using silica gel. The parameters, such as the temperature (40°C), the pH value of the gel (4, 4) and the concentration of the solution (1.0M solution of calcium chloride) are found to be critical. The crystals grown under these critical conditions are found to be ferroelectric. The ferroelectricity in these crystals has been established by hysteresis loop measurements, the loop turning into a narrow ellipse at 123°C, the Curie temperature. This observation has been supported by dielectric and thermal expansion measurements. The dielectric constant (K) at room temperature (∼30°C) is found to be 14.3 at 102 Hz which increases abruptly up to 93 at 123°C; beyond this temperature, K follows the Curie-Weiss law. There is also an abrupt change in the thermal expansion coefficient at 123°C. All these measurements show that calcium tartrate crystals grown by a gel technique with the mentioned critical conditions exhibit ferroelectricity. © 1990.