ELECTRICAL-CONDUCTIVITY OF HYDROGENATED BARIUM-YTTRIUM CUPRATE AND OFOXIDIZED 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 (format ion of the hydrocuprate) and subsequent oxidation (formation of the ox yhydrocuprate). The hydrocuprate (x>0, -0.1<z<0) was synthesized by ex posing 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 hydrogenat ed ceramic of composition H2Ba2YCu3O6.9 with oxygen at 470 K at a pres sure of 70 kPa. The four-probe de method was used in the electrophysic al measurements. The measurements were performed in the temperature in terval 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 m agnitude with hydrogenation from x=0 to x=2, and decreases by three or ders 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 s ystem. (C) 1997 American Institute of Physics.