THE EFFECT OF OXYGEN AND LEAD DOPING ON ELECTRICAL AND OPTICAL-PROPERTIES OF HIGH T-C GDBA2(CU1-XPBX)(3)O-DELTA COMPOUND SUPERCONDUCTORS

A systematic study of the electrical and infrared properties of the hi gh critical temperature, T-c, compound superconductor GdBa2(Cu1-xPbx)( 3)O-delta has been performed. Resistivity and a.c. susceptibility meas urements show a significant drop in T-c when copper is replaced by lea d in the range 0.005 less than or equal to x less than or equal to 0.0 25 Infrared measurements show that the conductivity of the compound in creases with the increase in lead concentration. For undoped samples, all the Restrahlen vibrations, common to these materials, are present in the infrared reflectance spectra. As the concentration of lead is i ncreased, a shift of the phonon modes, as well as broadening of the 15 0 cm(-1) phonon mode, is observed. Also the Restrahlen vibration aroun d 410 cm(-1) present in the normal material starts to disappear. This 150 mode is attributed to a change in the oxygen concentration, and is shown to be correlated with the critical temperature.