Metal-insulator transition and superconductivity in the LiTi(2-x)M(x)O(4) (M=B,Ni) spinel system

We have investigated the electrical conductivity and superconductivity of LiTi(2-x)M(x)O(4) (M = B,Ni) as a function of the dopant content (x). Polycrystalline samples of LiTi(2-x)M(x)O(4) were prepared from powders by sintering. It is the first time that these compounds have been prepared. The composition was determined by X-ray powder diffraction. Resistivity measurements in the temperature range of 12-300 K were used to study the effects of dopant substitution and sample preparation conditions on metal-insulator transition (MIT) and T-c. These measurements reveal two common features of the MIT, First, the average valence of the titanium is almost constant at the MIT, and second, the change of the position of the oxygen anion during the transition was in the same direction in all measurements. Comparison of our current and previous results with published works, in which other ions were substituted for Ti in LiTi2O4, reconfirm our previous conclusion that the main factor that determines the MIT is the average valence of the titanium.