CRYSTAL-GROWTH OF SUPERCONDUCTING LITI2O4

Crystals of LiTi2O4, a member (s = 1) of the hypothetical LiTi(III)4-3 sTi(IV)2s-1O4 (0.50 less-than-or-equal-to s less-than-or-equal-to 1.33 ) spinel series, were grown by two methods: electrolysis (30 mA, 100 m V) of a bath containing a suspension of TiO2 (anatase) in molten LiBO2 , and chemical reduction by addition of a metal, Zr, more electroposit ive than Ti, on the indicated suspension. LiTi2O4 crystals were charac terized by energy dispersive spectroscopy (EDS), X-ray powder diffract ion and scanning electron microscopy. Electrolysis led to crystal aggr egates of about 1 mm3, grown on the cathode and to skeletal crystals, 0.15 mm3, of cubic morphology related to the development of growth spi rals in the three directions. The reduction using Zr plates gave rise to rows of twinned crystals as well as to isolated crystals showing pl anar faces unequally developed. The crystal structure of LiTi2O was an isotropically refined by single-crystal X-ray diffraction in space gro up Fd3mBAR (No. 227), with a = 8.372(1) angstrom, V = 586.8(1) angstro m3, Li and Ti at tetrahedral and octahedral sites, respectively, an ox ygen parameter u = 0.2628(3) and, as a consequence, practically equal Li-O and Ti-O distances. As is shown by AC susceptibility measurements , electrolytically grown crystals as well as those grown on Zr plates are very similar in their superconducting transitions, with T(c) (onse t) of 11.5 K, transition widths of 1.5 K, and diamagnetic shieldings o f 65-70%. Magnetization measurements up to 2 T at 6 K on electrolytica lly grown crystals show a lower critical field H(c1) of 250 Oe and a c ritical current of 106 A CM 2.