PHYSICAL-PROPERTIES AND PHASE-TRANSITIONS OF BIS(GUANIDINIUM)ZIRCONIUM BIS(NITRILOTRIACETATE)HYDRATE, [C(NH2)(3)](2)ZR[N(CH2COO)(3)](2)CENTER-DOT-H2O

Large single crystals of optical quality of bis(guanidinium)zirconium bis(nitrilotriacetate)hydrate have been grown from aqueous solutions. Complete elastic, thermoelastic and piezoelastic tensors have been det ermined by ultrasonic methods. In addition, the tensor of thermal expa nsion, refractive Indices, dielectric and piezoelectric constants have been studied in the range between 210 K and 330 K. Most physical prop erties investigated show a strong anisotropy. The piezoelectric consta nt d(123) exceeds d(111) of alpha-quartz by a factor of 25. Two higher -order phase transitions appear at about 287 K and 290 K. The intermed iate phase exhibits strong anomalies of the temperature and pressure d ependence of the propagation velocities of quasi-longitudinal elastic waves having a large component of the displacement vector parallel to [010].