Topologically prone or cation compression restricted phase transition: An example of feldspar-related SrGe2B2O8

The stability and phase transformation processes of SrGe2B2O8 were studied under extreme conditions (up to 960 C / 40 GPa) using in situ single-crystal and powder X-ray diffraction. The compound demonstrated stability up to 900 degrees C, when it starts to decompose to SrGe4O9 and Sr2B2Ge4O14. Under high-pressure (HP) conditions SrGe2B2O8 undergoes two phase transitions, accompanied by formation of B2O7 dimers and stepwise increasing of Ge coordination number from 4 to 6 through the 5-coordinated polyhedron. This unusual stepwise increase in the coordination number of the framework cation is consistent with the behavior of silicon in isostructural CaSi2B2O8, suggesting that certain topologies are prone to similar effects. We also assume that observed differences in HP behavior of isostructural paracelsian-like phases is caused by different compression capacities of tetrahedral cations (Si, Al, B).(c) 2022 Elsevier B.V. All rights reserved.

Automated summary

The stability and phase transformation processes of SrGe2B2O8 were investigated under extreme conditions. The compound demonstrated stability up to 900℃, but decomposed at higher temperatures. Under high-pressure conditions, SrGe2B2O8 underwent two phase transitions accompanied by the formation of B2O7 dimers and an increase in Ge coordination number. The observed behavior was consistent with the behavior of silicon in a similar compound.