Electrical conductivity of hydrogenated barium-yttrium cuprate and of oxidized hydrocuprate in the 300-450 K interval

The electrical conductivity of ceramic samples with a general formula H2Ba2YCU3O7+z has been measured in the course of hydrogenation (formation of the hydrocuprate) and subsequent oxidation (formation of the oxyhydrocuprate). The hydrocuprate (x>0, -0.1<z<0) was synthesized by exposing the parent Ba2YCu3O6.9 ceramic to hydrogen at a temperature of 450 K and a pressure of 50 kPa. The oxyhydrocuprate (x=2, z less than or equal to 1.5) was prepared by treating the preliminarily hydrogenated ceramic of composition H2Ba2YCu3O6.9 with oxygen at 470 K at a pressure of 70 kPa. The four-probe de method was used in the electrophysical measurements. The measurements were performed in the temperature interval 300-450 K and within the compositional ranges 0<x<2.1, -0.1<z<1.5. The resistivity of the samples increases by nearly six orders of magnitude with hydrogenation from x=0 to x=2, and decreases by three orders of magnitude with oxidation, changing from z=-0.1 to z=0.8 for x=2. The electrode polarization effect is observed, which is apparently caused by ionic processes occurring at the electrode-ceramic interface. Water vapor is experimentally found to exert considerable effect on the electrophysical parameters of the hydrocuprate-copper electrodes system. (C) 1997 American Institute of Physics.