Hydrothermal crystallization in the systems LiOH-MO2-GeO2-H2O (M = Ti, Sn) at 500°C and 0.1 GPa:Li2Ti[5]Ge[4]O5 and Li2Ge[6]Ge2[4]O6 phase relations

Abstract

Crystallization in the LiОH–TiО2–GeО2–H2O and LiOH–SnO2–GeO2–H2O hydrothermal systems was studied at 500°C and 0.1 GPa. The phases crystallizing in the Ti system are Li2Ti[5]Ge[4]O5 , Li2Ge[6]Ge2[4]O6(OH)2 , Li3HGe4[6]Ge3[4]O16 · 4H2O, and Li2Ge[4]O3 (Ge in four- or sixfold oxygen coordination, and Ti in fivefold oxygen coordination). Over a wide range of TiO2 : GeO2 molar ratios (6 : 1 to 1 : 1), the dominant phase is Li2Ge[6]Ge2[4]O6(OH)2 . At higher GeO2 contents (TiO2 : GeO2 = 1 : 2 to 1 : 6), both Li2Ti[5]Ge[4]O5 and Li2Ge[6]Ge2[4]O6(OH)2 crystallize. The crystallization fields of Ge-containing phases at TiO2 : GeO2 = 1 : 2 to 1 : 6 are (in order of increasing LiOH concentration) GeO2 (rutile structure), Li2Ti[5]Ge[4]O5 + Li2Ge[6]Ge2[4]O6(OH)2, and Li2Ti[5]Ge[4]O5 + Li2Ge[6]Ge2[4]O6(OH)2 + Li2Ge[4]О3 + Li3HGe4[6]Ge3[4]O16 · 4H2O. The phases crystallizing in the Sn system are Li2Ge[6]Ge2[4]O6(OH)2, Li3HGe4[6]Ge3[4]O16 · 4H2O, and Li2Ge[4]O3. Tin is present in the form of SnO2 only. The structures of Li2Ti[5]Ge[4]O5 and Li2Ge[6]Ge2[4]O6(OH)2 are characterized by the simplest type of matrix assembly: direct packing of substructural precursor units and their two-dimensional growth in various crystallographic directions.