Metastable phase diagram of Bi probed by single-energy x-ray absorption detection and angular dispersive x-ray diffraction

In this paper we report the results of a detailed experimental study of samples composed of micrometric Bi droplets providing an insight into the metastable phase diagram of Bi. To this purpose we have used the single-energy x-ray absorption detection technique in combination with angular dispersive x-ray diffraction available at the BM29 beamline of the European Synchrotron Radiation Facility. This unconventional approach has given proof of being a different and reliable tool for detecting subtle structural modifications in condensed matter. The investigation has revealed a large variety of metastable Bi polymorphs in a broad range of pressures and temperatures (25-500 °C, 0-6 GPa) and the occurrence of a Bi crystalline structure isomorphic to the beta-tin structure. We have shown that the range of undercooling of liquid Bi strongly depends upon pressure and the underlying solid stable and metastable phases. As a final result a Bi-phase diagram including metastable phases is proposed, which takes into account all structural information obtained from this experiment.