A HIGH-TEMPERATURE MOSSBAUER-EFFECT STUDY OF IRON-DOPED YBA2CU3O7 SUPERCONDUCTOR

Superconducting YBa2Cu2.955Fe0.045O7 has been studied at temperatures between 300 and 1000 K. Spectra were recorded on a sample which was se aled as a pellet pressed with boron nitride. An atmosphere of oxygen w as maintained in the sample region at all times. At temperatures up to 900 K, we observed the four iron sites A, (Cu(1) chain-site; square p lanar oxygen coordination with O(5) vacancy on the a-axis), B, (Cu(2) plane-site; square pyramidal oxygen coordination), C, (Cu(1) chain-sit e; square pyramidal oxygen coordination with O(5) site occupied) and D , (Cull) chain-site; quasi-tetrahedral oxygen coordination with O(4) v acancy along the b-axis). At temperatures up to 700 K, the relative ar ea of the B and C sites remained nearly constant as the temperature wa s increased. However, the area of the A site decreased while, the D si te area increased with increasing temperature. At all times, the total area of sites A and D remained constant, thereby indicating the possi bility of oxygen atom hopping in the a-b plane. The quadrupole splitti ng of each site, except the B site, decreased linearly with increasing temperature.