Bi2Ge2O7 crystalline structure: a new metastable compound discovered in the Bi2O3–GeO2 system

The paper reports on the crystalline structure of a new metastable compound (Bi₂Ge₂O₇) found in the Bi₂O₃–GeO₂ system. This new phase was synthesized from powders by slow cooling of the melt in a platinum container from 1125 °C. The X‑ray diffraction analysis was used to determine the monoclinic lattice parameters of the crystalline structure (a = 14.81691(4) Å, b = 5.28586(1) Å, c = 9.45669(4) Å, β = 124.4766(2) deg., V = 610.560(3) ų) and space group C2/c. The sample also contains a small admixture of α‑quartz-type GeO₂ (up to 2 wt. %), which could not be removed at this stage of research. Scanning electron microscopy and energy dispersive analysis revealed that the synthesized samples consist of Bi₂Ge₂O₇ plates and Bi₂Ge₂O₇+GeO₂ mixture, which is formed along the plate boundaries. The ratio of the initial components (32:68 mol. %) is the most optimal, as it allows obtaining the minimum content of impurity phase (GeO₂).