Thermomechanical detwinning of superconducting YBa sub 2 Cu sub 3 O sub 7 minus x single crystals

A method for the complete removal of twins from single crystals of superconducting YBa{sub 2}Cu{sub 3}O{sub 7{minus}{ital x}} is described. The process depends on ferroelastic behavior found to exist in the phase, and should be generally applicable to the layered perovskite-type phases containing accommodation twins resulting from a tetragonal-to-orthorhombic transformation on cooling. The twin-free, superconducting single crystals will enable investigation of {ital a}-{ital b} anisotropy of properties as well as crystal structure determination without complication by the presence of microtwins.