PREPARATION AND CRYSTAL-STRUCTURE OF LI6ZR2O7 AND LI6HF2O7

Li6Zr2O7 was obtained by annealing an intimate mixture of LiOH . H2O a nd freshly prepared ZrO2 in a stream of argon. It is monoclinic: C2/c, a = 1 044.5(1), b = 598.9(1), c = 1020.0(1) pm, beta = 100.26(1)-degr ees, Z = 4, R = 0.016 for 1218 F values and 55 variables. The structur e is closely related to that of NaCl with an ordered distribution of t he metal atoms on the sodium sites while the oxygen atoms occupy seven eighths of the chlorine positions. Li has square pyramidal, Zr octahe dral oxygen coordination. The corresponding Hf compound is isotypic: a = 1 040.2(1), b = 596,2(1), c = 101 5.0(1) pm, beta = 100.36(1)-degre es. Li-7 nuclear magnetic resonance spectra of this compound give no i ndication for a high mobility of the Li+ ions.