CRYSTAL-GROWTH OF SUPERCONDUCTING LITI2O4

Crystals of LiTi2O4, a member (s = 1) of the hypothetical LiTi(III)4-3sTi(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 mV) of a bath containing a suspension of TiO2 (anatase) in molten LiBO2, and chemical reduction by addition of a metal, Zr, more electropositive than Ti, on the indicated suspension. LiTi2O4 crystals were characterized by energy dispersive spectroscopy (EDS), X-ray powder diffraction and scanning electron microscopy. Electrolysis led to crystal aggregates of about 1 mm3, grown on the cathode and to skeletal crystals, 0.15 mm3, of cubic morphology related to the development of growth spirals in the three directions. The reduction using Zr plates gave rise to rows of twinned crystals as well as to isolated crystals showing planar faces unequally developed. The crystal structure of LiTi2O was anisotropically refined by single-crystal X-ray diffraction in space group Fd3mBAR (No. 227), with a = 8.372(1) angstrom, V = 586.8(1) angstrom3, Li and Ti at tetrahedral and octahedral sites, respectively, an oxygen 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) (onset) of 11.5 K, transition widths of 1.5 K, and diamagnetic shieldings of 65-70%. Magnetization measurements up to 2 T at 6 K on electrolytically grown crystals show a lower critical field H(c1) of 250 Oe and a critical current of 106 A CM 2.