Abstract

We discovered a new CaGe2O5 polymorph in high-pressure experiments (above 8 GPa). The phase is orthorhombic, space group Pbam, with a = 7.306(2), b = 8.268(2), c = 5.714(1) Å, V = 345.2(1) Å3, and Z = 4. The new phase, which we call post-titanite CaGe2O5, is the high-pressure polymorph of titanite CaGe2O5. The structure of this new polymorph is based on a network of 5- and 6-coordinated Ge polyhedra and 8-coordinated Ca atoms. Following the germanate analog to silicate, post-titanite CaSi2O5 could be expected to form at high-pressure conditions and thus might exist in Earth’s mantle.

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