LOCALIZED-ITINERANT ELECTRONIC-TRANSITION IN THE PEROVSKITE SYSTEM LA1-XCAXVO3

The insulator-metal (I-M) transition near the critical composition x(c ) approximate to 0.26 in La1-xCaxVO3 is confirmed, as is the apparent existence of a solid solution over the entire compositional range 0 le ss than or equal to x less than or equal to 1 according to room-temper ature powder x-ray diffraction. Although interpretation of the evoluti on with x of its physical properties would seem to require a global el ectronic model, the magnetic and transport properties we measure below room temperature suggest the presence of a two-phase electronic model with itinerant-electron behavior in hole-rich (or electron-poor) doma ins and localized-electron behavior in hole-poor domains. Localized el ectronic states within the itinerant-electron domains are associated w ith atomic vacancies or lattice defects. The system may remain atomica lly disordered, but an electronic phase segregation can be accomplishe d at lower temperatures by cooperative oxygen-atom displacements. Sepa ration into electronically distinguishable phases by this mechanism wo uld not be detected easily by powder x-ray diffraction. A first-order structural phase transition occurs in the interval 400-640 K for all x ; the high-temperature phase exhibits a Curie-Weiss paramagnetism.