SYSTEMATIC STUDY OF INSULATOR-METAL TRANSITIONS IN PEROVSKITES RNIO3 (R = PR, ND, SM, EU) DUE TO CLOSING OF CHARGE-TRANSFER GAP

The detailed behavior of the phase transitions was mapped out for the series RNiO3 as a function of the rare earth (R). A sharp insulator-metal transition is observed, which depends strongly on R. For small R it occurs at a higher temperature than the antiferromagnetic ordering (measured by muonspin relaxation). By increasing either the temperature or the size of R, an insulator-metal transition is observed, most probably caused by the closing of the charge-transfer gap, induced by an increase in the electronic bandwidth.