PHASE-TRANSITION IN THE ELECTRON SUBSYSTEM OF HIGH-TC YBA2CU3O7

Time-dependent XRD and resistivity data on the orthorhombic high-Tc (T -c greater than or equal to 90K) YBa2Cu3O7 (123) phase at the low temp erature transformation YBa2Cu3O7 --> YBa2Cu4O8 (124) are presented. Th is transformation is accompanied by the phase separation of mother's 1 23 structure into two 123 structures. We analyse the difference in the structures and the electrophysical features of these two phases and r eveal that two qualitatively different HTS states of the electron subs ystem may exist in the orthorhombic 123 structure as function of the t ype and a degree of its cation subsystem imperfection.