Phase separation in degenerate magnetic oxide semiconductors

A theory of mixed electronic-impurity phase separation in degenerate magnetic oxide semiconductors, including high-T _c superconductors and materials with colossal magnetoresistance (CMR), is developed. Such a separation can occur in materials with excess oxygen, if they are simultaneously doped with an acceptor impurity whose atoms are frozen in position. Oxgyen acts as an acceptor, which can diffuse through the crystal. Then, for example, manganites can break up into ferromagnetic and antiferromagnetic regions with all holes and oxygen ions concentrated in the former and with no holes or oxygen ions in the latter. Such two-phase systems can possess CMR and anomalous thermoelectric power, and they can make a transition from an insulating into a highly conducting state as temperature increases. The reverse insulator-metal transition is also possible. Fiz. Tverd. Tela (St. Petersburg) 40, 2069–2073 (November 1998)