POLARON TRANSPORT IN YBA2CU3OY INSULATORS

The (bi)polaron formation in metal oxides is considered as one of the real mechanisms responsible for high temperature superconductivity. Bu t investigation of polaron characteristics in metals is complicated by charge screening. The paper reports the investigation of low-frequenc y conductivity sigma of oxygen deficient YBa2Cu3Oy samples (6.17 less than or equal to y less than or equal to 6.31). The measurements are c arried out in a frequency range from 0.3 to 100 kHz at temperatures 1. 5 K < T < 300 K. It is shown that sigma(T) = sigma(0) + A omega(S), om ega = 2 pi f being the measuring frequency. The temperature dependence s(T) is found to have an anomaly - a temperature minimum. The observe d anomaly is described in terms of the theory of large radius polaron tunneling [4]. The theory permits the polaron bond energy and the pola ron radius to be estimated. A treatment of the oxygen content dependen ce of the polaron bond energy is proposed.