Structural transformations of Bi2CuO4 induced by mechanical deformation

Structural transformation of α-Bi2CuO4 (a=8.4996 Å, c=5.8172 Å, space group P4/ncc) during ball milling was investigated by powder x-ray diffraction and thermal analysis. It is shown that α-Bi2CuO4 first transforms into an amorphous phase; and then transforms into a new phase (designated by β-Bi2CuO4) with milling time. The new phase appears to be isostructural to (La,Sr)2CuO4 and has a tetragonal cell with cell parameters a=3.869 and c=13.83 Å. It is a metastable phase which can transform back into α-Bi2CuO4 at 650 °C. No superconductivity was observed above 5 K for both as-milled samples and oxygen-annealed β-Bi2CuO4.