Unusual aspects of pressure-induced phase transitions in CuGeO₃

Abstract

High pressure Raman and optical studies on the spin-Peierls compound CuGeO₃ have revealed three novel pressure-induced phase transitions in the 7-8 GPa range. Once of these occurring only under hydrostatic conditions, is belived to be a ferroelastic-ferroelectric phase. The other two high pressure phase are brilliant blue and green, respectively. Of these, the blue-phase is quenchable, while the green-phase reverts to the blue. From crystal chemistry, Raman spectral features and metastability considerations, it is suggested thet the blue and the green phases have the pyroxene type chain structure similar to enstatite polymorphs, and non-hydrostatic pressure is essential for the formation of pyroxene type chain structures.