Superconductivity and New Compounds in the Bi-O-S System

Recent reports of superconductivity in Bi$_4$O$_4$S$_3$ and LaO$_{1-x}$F$_x$BiS$_2$ have stimulated interest in a potentially new family of layered superconductors based on BiS$_2$ units. The most interesting structural feature of the reported crystal structure of Bi$_4$O$_4$S$_3$ is that it contains both reduced sulfides (S$^{2-}$) and oxidized sulfates (S$^{6+}$) within the same compound. However, the scattering factors of oxygen and sulfur relative to bismuth make the precise structure of Bi$_4$O$_4$S$_3$ difficult to determine by x-ray diffraction, and limit the ability to compare with theoretical predictions of electronically driven structural distortions. Here we report the results of studies on the structure and physical properties of compounds in the Bi-O-S system through electron diffraction, high resolution transmission electron microscopy, synchrotron x-ray diffraction, and IR spectroscopy, including the discovery of two new ternary Bi-O-S phases.