抄録
The system (Li1-xMx)Ti2O4 (M=Mg, Be) with the spinel structure was prepared by firing twice a mixture of the component oxides, i.e., Li2O, MgO, BeO, Ti2O3, and Ti02 at 1073K for 12 h in vacuo(ca. 10-5 Torr). The lattice constants were obtained by the powder X-ray diffractometry whereas the molar fraction of Ti3+ ions in the total Ti atoms, i.e., f (%) was determined by thermogravimetry. The critical temperatute Tc(K, mid-point) was obtained by using a usual four-probe resistivity measurement in the range of 300 K to ca. 2 K. As a result, the cubic lattice constant a(A) of the system linearly increased as the molar ratio f increased. However, it was found that Be2+ with a much smaller ionic radius than that of Li+ can hardly replace the Li+ site of the spinel structure, as implied from the plots of the lattice parameter a and the chemical composition x. The highest Tc was observed at f=ca. 50 % in the composition Li1+xXTi2-xO4, and the Tc suddenly decreased as either the molar ratio f or the lattice constant a decreased. On the other hand, the Tc of the composition (Li1-xMgx)Ti2O4 gradually decreased as either the molar ratio f or lattice constant a increased.
