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 po wders by sintering. It is the first time that these compounds have bee n prepared. The composition was determined by X-ray powder diffraction . Resistivity measurements in the temperature range of 12-300 K were u sed to study the effects of dopant substitution and sample preparation conditions on metal-insulator transition (MIT) and T-c. These measure ments reveal two common features of the MIT, First, the average valenc e of the titanium is almost constant at the MIT, and second, the chang e of the position of the oxygen anion during the transition was in the same direction in all measurements. Comparison of our current and pre vious results with published works, in which other ions were substitut ed for Ti in LiTi2O4, reconfirm our previous conclusion that the main factor that determines the MIT is the average valence of the titanium.