Influence of synthesis route on structural phase transition in YBa2−xLaxCu3Oy (0<x<0.20)

The compounds YBa2−xLaxCu3Oy, with compositions (0<x<0.20), have been synthesised by nitrate decomposition method and solid-state reaction and characterised. Structural transition from orthorhombic to tetragonal phase occurred at (0.15<x<0.20) in compounds synthesised by nitrate decomposition method, whereas no transition was observed in compounds synthesised by solid-state reaction for x values up to 0.20. The ternary phase formation temperature is influenced by the starting materials used and ionic size considerations. These factors are shown to determine the composition at which the changeover from orthorhombic (superconducting) to tetragonal (non-superconducting) phase transition (O–T transition) occurs.