Microscopic electronic phase separation and metal-insulator transition inNd0.5Sr0.5MnO3

Microstructure related to the charge ordered (CO) state and metal-insulator (MI) transition in ${\mathrm{Nd}}_{0.5}{\mathrm{Sr}}_{0.5}{\mathrm{MnO}}_{3}$ 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 vicinity of the antiphase boundaries in the CO regions, which are closely related to the MI transition around 160 K. 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.