X-ray diffraction, magnetic, and transport study of lattice instabilities and metal-insulator transition in CaV1-xTixO3 (0≤x≤0.4) -: art. no. 245118

CaVO3 is metastable in air at room temperature. Measurements below room temperature on fresh, polycrystalline CaV1-xTixO3, 0less than or equal toxless than or equal to0.4 samples that were cold-pressed into dense pellets showed a resistivity rho(T)=rho(0)+aT(3/2) for x=0 and 0.05, but a rho(T)=rho(0)+bT(2) for x=0.1 and a transitional temperature dependence in x=0.2 and 0.3 to a rho(T)proportional toexp(T-0/T)(1/4) for x=0.4. The thermoelectric power shows no phonon-drag component in any sample and a systematic transition above 200 K from a small, temperature-independent behavior in CaVO3 to an unusual increase with temperature in the x=0.3 and 0.4 samples. A nearly temperature-independent paramagnetism above 150 K is enhanced relative to a conventional Pauli paramagnetism by two orders of magnitude, and the low-temperature paramagnetism is dominated by localized spins that exhibit a sharp increase in concentration in the range 0.2<xless than or equal to0.4. A small step increase of the linear variation of volume with x occurs at xapproximate to0.1. The solid-solution range does not extend significantly beyond x=0.4. These data are interpreted in terms of a first-order Mott-Hubbard transition manifesting itself as strong-correlation fluctuations in a narrow pi(*) band of the VO3 array in CaVO3 and an inability to obtain complete solid solution of the CaVO3-CaTiO3 system. Substitution of Ti(IV) introduces Anderson-localized states below a mobility edge mu(c) that increases with x, crossing epsilon(F) in the range 0.2<x<0.4. A trapping out of the strong-correlation fluctuations as localized V(IV): t(1)e(0) configurations is postulated to occur for xgreater than or equal to0.1.