Microscopic Electronic Phase Separation and Metal-Insulator Transition in Nd sub (0.5) Sr sub (0.5) MnO sub 3

Microstructure related to the charge ordered (CO) state and metal-insulator (MI) transition in Nd sub (0.5) Sr sub (0.5) MnO sub 3 was investigated by transmission electron microscopy. An in-situ observation on heating from the CO state revealed a drastic change in the microstructure: the nucleation and growth of the ferromagnetic (FM) charge-disordered regions proceed in the vicinty of the antiphase boundaries in the CO regions, which are closely related to the MI transition around 160K. These transition processes suggest that an abrupt increase in the electronic conductivity during the MI transition is mainly due to the percolation mechanism. Furthermore, the FM metallic phase is found to be characterized by a spatially fine mixture of incommensurate charge-ordered microdomains in the FM charge-disordered phase. This result clearly demonstrates the occurrence of microscopic-scale electronic phase separation in the manganese oxides.