(Ga,Ge)-Analogue of Tourmaline: Crystal Structure and Composition

Crystals of a (Ga,Ge)-analogue of tourmaline have been synthesized by hydrothermal method in the temperature range of 600–650°C under a pressure of 100 MPa. The composition is analyzed, and the structure of single crystals is determined by X-ray diffraction (XRD) analysis. The rhombohedral-cell parameters are found to be a = 16.0102(4) Å, c = 7.18423(19) Å, sp. gr. R3m, and Z = 3. The distribution of cations over nonequivalent sites in the structure under study is determined to be as follows: Na0.57(Al1.20Ga1.20 Fe_0.60^2 + )(Al4.728 Fe_1.20^2 + Ti0.072)((Si4.80Ge0.78Al0.42)O18)(BO3)3(OH)3(O0.42ОН0.58). The results obtained confirm possibility for obtaining Ge-substituted crystals with tourmaline structure, which (by analogy with the Ge-analogue of quartz) exhibit high piezo- and pyroelectric properties.