Structural aspects of pressure- and temperature-induced phase transitions in low-dimensional systems
This thesis reports on structural studies of low-dimensional systems MOCl (M = Sc, Ti, V, Cr, Fe) and TiPO4 subjected to non-ambient conditions. Transition metal oxychlorides MOCl have been investigated at high pressures in diamond anvil cells by means of single-crystal synchrotron X-ray diffraction and by complementary techniques including Raman and Mossbauer spectroscopies and powder X-ray diffraction. The results reveal a plethora of high-pressure phase transitions in MOCl. A structural analysis allowed to associate the driving forces of the transitions either with the optimization of crystal packing, with the enhancement of low-dimensional magnetic properties, or with changes in electronic structures. TiPO4 has been studied by means of single-crystal X-ray diffraction at low temperatures. A structural proof of the spin-Peierls transition in this compound has been obtained. Furthermore, a novel incommensurately modulated phase of TiPO4 has been discovered and characterized.
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