A high-pressure X-ray powder diffraction and infrared study of copper germanate, a high-Tcmodel

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Abstract
Copper germanate has been examined by synchrotron X-ray powder diffraction at high pressure in a diamond anvil cell at pressures up to 220 kbar, and by infrared spectroscopy to 162 kbar. These concur in showing a phase transition at 66-73 kbar: the X-ray powder diffraction data have been indexed successfully on the basis of a P21/a cell, deduced from a model of the phase change in which germanate chains slip relative to each other along their axes. Slow changes in diffraction pattern form 110-220 kbar suggests existence of a further, very sluggish, phase change. CuGeO3 turns black near 5 kbar due to a band shift. Contraction of the orthorhombic cell constants of the initial phase is markedly anisotropic, the principal changes being in the plane which contains the long Cu-O bonds. These are twice as easily compressed as the short Cu-O bonds.

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