Investigation of the dielectric properties of BaTi[O.sub.3] single crystals of different qualities by the thermal noise method

Comparative dielectric investigations of bulk barium titanate crystals grown using different techniques have been performed by the thermal noise and traditional methods. The temperature dependences of the permittivity have been used to determine the phase transition temperatures and the Curie--Weiss constants. The investigation performed using the thermal noise method has revealed a number of phenomena that complicate the separation of the noise associated with the change in the impedance of the sample. Possible approaches to the elimination or minimization of contributions from different effects to the total noise voltage have been described. The piezoelectric resonances that also contribute to the total noise signal have been found for the first time and investigated by the thermal noise method. The possible nature of the obtained temperature dependences of the piezoelectric resonance frequencies has been discussed.