Metal–Insulator Transition and Crystal Structure of La1-xSrxCoO3as Functions of Sr-Content, Temperature, and Oxygen Partial Pressure

Electrical properties of La1-xSrxCoO3(LSC) change with variations in Sr content, temperature, and oxygen partial pressure. With a change in each variable, LSC showed metal–insulator transition (MIT). The changes in electrical properties of LSC Awere correlated here with those of its crystal structure. The variations of crystallographic parameters such as the length ofaaxis, the rhombohedral angle, the Co–O distance, and the Co–O–Co angle () were precisely determined by powder X-ray Rietveld analysis. Of these, the variation ofdescribed most consistently the variation of conduction state, metallic or insulating, of LSC. The Co–O–Co angle increased whenever the conduction state changed from insulating to metallic by changing each variable, Sr content, temperature, and oxygen partial pressure. In addition, MIT took place at a critical Co–O–Co angle of ca. 165° in each case. It was concluded that the transition from insulator to metal is caused by the closing of the charge transfer band gap, induced by broadening of the electronic bandwidths of the Co-3dand O-2pbands with an expansion of the Co–O–Co angle.