Orthoenstatite to forsterite phase transformation in magnesium germanate ceramics

Magnesium germanate (MgGeO3) ceramics represent a model system for geological study of the upper earth's mantle and are recently being investigated for applications in which red luminescence properties are required. The mechanical and optical properties of MgGeO3 are greatly influenced by the its polymorphic nature and by the complex series of phase transformations taking place in response to temperature variations and the application of mechanical pressure, as well-documented in the literature. In the present study, an additional phase transformation from orthoenstatite MgGeO3 to forsterite Mg2GeO4 with an olivine-type structure is identified in ceramics sintered in range 1350–1500 °C and ascertained by the refinement of the relative X-ray diffraction patterns. The phase transformation is believed to be driven by the volatilization of GeO2 during high-temperature sintering and it should be taken into consideration when targeting single phase and dense MgGeO3 ceramics.