Crystal structure, phase transition, and ion dynamics in Li(NH4)(6)Zr4F23

The crystal structure was determined for the Li(NH4)(6)Zr4F23 compound. The crystals are orthorhombic: a = 15.250(2), b = 12.033(2), c = 6.584(1) Angs trom, space group Immm, Z = 2, rho(calcd) = 2.52 g/cm(3), R = 0.042, and R- w = 0.048. The structure is built from isolated [Zr4F23](infinity)(7-) chai ns surrounded by Li+ and NH4+ cations. The crystals of Li(NH4)6Zr4F23 were found to undergo polymorphic transformation at T approximate to 415 K. The dynamics of fluoride and ammonium ions in this compound was studied by H-1 and F-19 NMR spectroscopy over a temperature range of 170-440 K. The types of internal motion were determined, and their activation energies were esti mated.