A high temperature Mössbauer effect study of iron-doped YBa2Cu3O7 superconductor

Superconducting YBa₂Cu_2.955Fe_0.045O₇ has been studied at temperatures between 300 and 1000 K. Spectra were recorded on a sample which was sealed as a pellet pressed with boron nitride. An atmosphere of oxygen was 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 planar oxygen coordination with O(5) vacancy on thea-axis), B, (Cu(2) plane-site; square pyramidal oxygen coordination), C, (Cu(1) chain-site; square pyramidal oxygen coordination with O(5) site occupied) and D, (Cu(1) chain-site; quasi-tetrahedral oxygen coordination with O(4) vacancy along theb-axis). At temperatures up to 700 K, the relative area of the B and C sites remained nearly constant as the temperature was increased. However, the area of the A site decreased while, the D site area increased with increasing temperature. At all times, the total area of sites A and D remained constant, thereby indicating the possibility of oxygen atom hopping in thea-b plane. The quadrupole splitting of each site, except the B site, decreased linearly with increasing temperature.Research supported in part by the Old Dominion University Undergraduate Research Program.