Phase relations in the systems LiOH-GeO2-H2O and LiOH-SiO2-H2O at 500°C and 0.1 GPa

Crystallization in the LiOH-GeO2-H2O and LiOH-SiO2-H2O hydrothemal systems was Studied at 500degreesC and 0.1 GPa. The systems were shown to contain both the isostructural compounds Li2SiO3 and Li2GeO3 and phases differing in crystal chemistry: Li2Si2O5, Li2Ge3O6(OH)(2), and Li3HGe7O16 . 4H(2)O (containing Ge in different oxygen coordinations). The crystallization fields revealed in the germanate system are (in order of increasing, LiOH concentration) GeO2 => GeO2 + Li2Ge3O6(OH)(2) double right arrow Li2Ge3O6(OH)(2) + Li2GeO3 => Li3HGe7O16 . 4H(2)O + Li2GeO3; those in the silicate system are alpha-SiO2 double right arrow alpha-SiO2 + Li2Si2O5 => Li2Si2O6 + Li2SiO3 double right arrow Li2SiO3. Increasing the LiOH concentration increases the number of Li atoms per tetrahedrally coordinated Si or Ge atom in the crystallizing compounds. The high stability of Li2Ge3O6(OH)(2) is interpreted in terms of the matrix assembly of the structure from cyclic invariant subpolyhedral structural units.