Anderson-Mott transition induced by hole doping in Nd1−xTiO3

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 0.010(6)≤x≤0.243(10). Insulating p-type conduction is found for x≤0.071(10). Anderson localization in the presence of a Mott-Hubbard gap is the dominant localization mechanism for the range of 0.074(10)≤x<0.089(1) samples. For x≥0.089(1), n-type conduction is observed and the activation energy extrapolates to zero by x≅0.1. The 0.095(8)≤x<0.203(10) 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 T2 coefficients. For 0.074(9)≤x≤0.112(4), a weak negative magnetoresistance is found below ∼15K and it is attributed to the interaction of conduction electrons with Nd3+ 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.