Structural and electronic phase transitions of Co_{2}Te_{3}O_{8} spiroffite under high pressure

The structural and electronic phase transitions of Co 2 Te 3 O 8 spiroffite have been studied with a suite of in situ high-pressure characterization techniques including synchrotron X-ray diffraction, Raman, X-ray emission spectroscopy, UV-Vis absorption, and electrical transport measurement. Two pressure-induced phase transitions were observed at about 6.9 GPa and 14.4 GPa. The first transition is attributed to a small spin transition of Co along with discontinuity in unit cell volume change, while the second one represents a first order phase transition with a volume collapse of 4.5%. The latter transition is accompanied by the relaxation of distortion in CoO 6 octahedron, which enhances the crystal-field strength inhibiting the occurrence of spin transition. What’s more, the competition between contributions of electrons and oxygen ion to the overall conductivity is observed and affected by the phase transition under high pressure. This demonstration provides new insights into the relationship between the lattice-structural and spin degrees of freedom, and highlights the impact of pressure on the control of structural and electronic states of a given material for optimized functionalities.