Localized-itinerant and Mott-Hubbard transitions in several perovskites

The localized-itinerant and Mott-Hubbard transitions in single-valent perov skites are distinguished. The approach to the Mott-Hubbard transition from the itinerant-electron side is characterized by the appearance of strong-co rrelation fluctuations within a metallic matrix; these fluctuations introdu ce a Curie-Weiss paramagnetism that is added to a strongly enhanced Pauli p aramagnetism. As the critical bandwidth is approached, ordering of the stro ng-correlation fluctuations into a charge-density wave (CDW) may compete wi th a global Mott-Hubbard transition. The approach to the localized-itineran t electronic transition from the localized-electron side is illustrated by LaMnO3, where orbital ordering localizes the electrons of e-orbital parenta ge. In the mixed-valent La1-xSrxMnO3 system, the doped holes evolve from sm all polarons to two-manganese Zener polarons to itinerant-electron behavior . The Zener polarons order at low temperatures into a CDW.