Anderson-Mott transition induced by hole doping in Nd 1 − x TiO 3

The insulator/metal transition induced by hole doping due to neodymium vacancies of the Mott-Hubbard antiferromagnetic insulator, Nd1�xTiO3, is studied over the composition range 0.0106x 0.24310. Insulating p-type conduction is found for x 0.07110. Anderson localization in the presence of a Mott-Hubbard gap is the dominant localization mechanism for the range of 0.07410x 0.0891 samples. For x 0.0891, n-type conduction is observed and the activation energy extrapolates to zero by x 0.1. The 0.0958x 0.20310 samples are Fermi-liquid metals and the effects of strong electronic correlations are evident near the metal-to-insulator boundaries in features such as large Fermi liquid T 2 coefficients. For 0.0749x 0.1124, a weak negative magnetoresistance is found below 15 K and it is attributed to the interaction of conduction electrons with Nd 3+ magnetic moments. Combining information from our companion study of the magnetic properties of a Nd1�xTiO3 solid solution, a phase diagram is proposed. The main conclusions are that long-range antiferromagnetic order disappears before the onset of metallic behavior, and that the Anderson-Mott transition occurs over a finite range of doping levels. Our results differ from conclusions drawn from a similar study on the hole-doped Nd1�xCaxTiO3 system, which found the coexistence of antiferromagnetic order and metallic behavior and that the Mott transition occurs at a discrete doping level.