Investigation of two-well potential of the apex oxygen in YBa2Cu2O7−x crystals by Raman spectroscopy

The dependence of oxygen modes intensity on pump power and temperature in YBa2Cu3O7−x single crystals with different oxygen contents (0<x<1) has been measured. When YBa2Cu3O6.5 crystals are heated, the peak intensity of the 500-cm−1 band (apex oxygen) decreases, that of the 590-cm−1 band (“defect” mode) increases, and the peak intensity of the 330-cm−1 band (plain oxygen) remains unchanged. The resonant dependence of the apex oxygen, and the intensity of the “defect” modes have also been measured. In order to explain the experimental results we suppose that the apex oxygen ion is in a double-well potential.