Dependence of the magnetic properties of YBa2Cu3Ox in the superconducting state on the oxygen content

The temperature and field dependences of the magnetization of polycrystalline YBa2Cu3Ox samples were determined in the superconducting state as a function of the oxygen content (6.24≤x≤6.9). A continuous increase in the volume of superconducting phase as a result of cooling, a scatter of the values of Tc, and a decrease of the upper limit of Tc on lowering of x were observed. In the range x>6.55 the samples contain only the orthorhombic phase, whereas in the x≤6.78 range even at temperatures T much-lt Tc the volume of the superconducting phase deduced from the static magnetic susceptibility was considerably less than half the volume of the sample after a correction for porosity. In samples with 6.55≤x≤6.78 the volume of the superconducting phase deduced from the dynamic susceptibility at frequencies from 300 Hz to 8 kHz was considerably greater than that found from static measurements: the difference was independent of the frequency throughout the investigated range, but it decreased on increase in temperature and disappeared at T = T* (x) < Tc