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.