Oxygen content, crystal structure and chemical expansion of PrBaCo2−xFexO6−δ double perovskites

Abstract

PrBaCo_2−xFe_xO_6−δ (x = 0–0.6) double perovskites were shown to have a tetragonal P4/mmm structure in air over the complete temperature range investigated despite the oxygen content reaching a threshold value of 5.5 at temperatures from 850 °C for x = 0 up to 1078 °C for x = 0.6. However the P4/mmm→Pmmm structure transition was found to occur in PrBaCo₂O_6−δ under reducing conditions at temperatures from 500 °C at pO₂ = 10⁻³ atm down to 350 °C at pO₂ = 10⁻⁴ atm. The lattice chemical expansion along the a-axis and contraction along the c-axis, with decreasing oxygen content, 6 − δ, were found to completely compensate each other in the double perovskites and, therefore, their volume chemical expansion became negligible. As a result the cell volume linearly increases with temperature contrary to simple cubic perovskites.