PHYSICAL-PROPERTIES OF K2ZNCL4

Large single crystals of orthorhombic K2ZnCl42) with optical quality have been grown by the Czochralski method. The elastic constants and their temperature and pressure derivatives have been determined from ultrasonic resonance frequencies of thick plates of different orientation and the shift of these frequencies induced by temperature and pressure changes, respectively. K2ZnCl4 shows a small elastic anisotropy. Measurement of the dielectric constant was made along the ferroelectric axis epsilon(a) in the temperature range from 303 K to 573 K. Epsilon(a) of K2ZnCl4 grown by the Czochralski-method shows a smaller thermal hysteresis at the incommensurate-commensurate transition point (403 K) than that of crystals grown from an aqueous solution. It explains that crystals grown by the Czochralski-method are more purified, the pinning effect is weakened. The thermal hysteresis occurs with the same width at 10 KHz, 100 KHz, 1 MHz and 10 MHz.