Phase separation in HTSC and related nonsuperconducting systems

Both the electronic and magnetoimpurity phase separations (PS) are investigated in quasi-two-dimensional HTSC and degenerate antiferromagnetic (AFM) semiconductors. In addition to the already known FM-AFM type of PS, the possibility of separation into the initial insulating AFM phase and high-conducting magnetically disordered phase or a changed AFM phase is proved. PS may strongly increase T-c of HTSC and in certain cases even cause the superconductivity in a part of the crystal. PS may also lead to metal-insulator transitions in nonsuperconducting materials.