Metal to Semiconductor Transition of Vacuum Annealed YBa2Cu3O7-x and Characterization of its Semiconducting State

Electrical resistance measurements have been conducted in YBa2Cu3O7-x in the temperature range 80-350 K before and after the metal to semiconductor-like transition induced by vacuum annealings at 570 and 640°C. In the semiconducting phase (7 - x = 6.2 ± 0.2), the temperature dependence of resistivity closely follows the exponential law of classical semiconductors with an energy gap Eg = 0.77 eV.