Alkali gallates with mullite-type structure

Silica-free alkali gallates with mullite-type structure were synthesized by reaction of a stoichiometric mixture of the nitrates with glycerol and subsequent thermal treatment between 700 and 900 °C. The crystallization behavior of the compounds has been studied: specimens of the type potassium gallate K0.67Ga63+O9.33 and rubidium gallate Rb0.67Ga63+O9.33 have been prepared. The lattice constants (potassium gallate: a = 8.0065(12) Å, b = 8.0063(10) Å, c = 3.0359(5) Å; rubidium gallate: a = 8.0106(17) Å, b = 8.0161(17) Å, c = 3.0439(6) Å) were determined by refinement of the X-ray powder diffraction patterns which show a very close relationship to the alkali aluminate compounds with mullite-type structure. Furthermore isotypes of the composition Me0.67+(Fe3+, Ga)6O9.33 and Me0.67+(Fe3+, Al)6O9.33 (Me+ = Rb or K) with an Fe(III) content of 20–30% have been prepared.