Crystal structure and thermal behavior of Bi6 Te2 O15 : investigation of synthetic and natural pingguite

The previously unknown crystal structure of pingguite was determined and refned from laboratory X-ray powder difraction data using a synthetic sample. Additional single crystal difraction of natural pingguite confrms that the crystal structure of the synthetic sample is identical to the natural mineral. This new crystal structure calls for a revised chemistry of the rare mineral pingguite to Bi6Te2O15 instead of the previously reported formula Bi6Te2O13. Pingguite contains TeVI only and not TeIV as previously reported. Pingguite undergoes an irreversible phase transition around 840 ◦C which is characterized by a loss of oxygen and a reduction from TeVI to TeIV resulting in a 훿-Bi2O3 like type structure. In addition, we report the Raman spectroscopic data on the natural pingguite.