Abstract
An opposite thermal dynamic change in superconducting and semiconducting cuprates of YBa2Cu3O7−x(Y-123) is observed. At 450 °C the superconducting Y-123 single crystal shows an endothermal anomaly and a weight loss, while the semiconducting one shows an exothermal anomaly and weight gain. High temperature x-ray diffraction reveals that the lattice parameters of the Y-123 crystal jump significantly at this temperature. A computer simulation demonstrates that the change of the lattice parameters can be related with the change of the lattice energy.