Evidence for two electronic phases in Y1−xLaxTiO3 from thermoelectric and magnetic susceptibility measurements

Structural, transport, and magnetic measurements on nearly oxygen stoichiometric samples of the system Y1−xLaxTiO3 and LuTiO3 have revealed that antiferromagnetic LaTiO3 is a p-type conductor with holes spread over more than 10 Ti-atom centers in itinerant-electron clusters having a motional enthalpy DHm=0.035 eV. With the substitution of Y for La, short-range orbital-order fluctuations introduce ferromagnetic interatomic spin-spin interactions that increasingly reduce the magnitude of the Weiss constant u and suppress TN as x decreases. The volume fraction of a localized-electron, orbitally ordered second phase containing smallpolaron holes increases with decreasing x,0.6 until it becomes the majority phase for xø0.3 with static orbital ordering below a temperature T * that increases as x decreases. The volume fraction of the ferromagnetic phase does not reach unity at x=0, but it approaches unity in LuTiO3. Antiferromagnetic interactions across orbital-order antiphase interfaces lowers to zero the remanence of the ferromagnetic phase. The data appear to distinguish an itinerant-electron antiferromagnetism in the La-rich samples from a localized-electron ferromagnetic phase with a cooperative Jahn-Teller distortion.