Temperature-dependent change of Cu-O bond in La2CuO4 and YBa2Cu3O7

Valence-band spectra of La₂CuO₄ and YBa₂Cu₃O₇ were obtained by using X-ray photoemission varying the temperature of the measurement (35, 260, 300, and 500 C). In La₂CuO₄ the broad band centred around 4eV splits into two peaks at 260 C. At both 35 and 500 C the spectra show almost similar shape. In YBa₂Cu₃O₇ the broad peak centred around 4eV splits into two peaks at 500 C. Below 300 C the spectra show almost similar shape. These splittings of the valence-band spectra may be due to the rearrangement of the crystal structure accompanying the phase transition from the orthorhombic to tetragonal symmetry.