How to Look for Compounds: Predictive Screening and in situ Studies in Na-Zn-Bi

Abstract

Here we demonstrate the combination of theoretical computations followed by rapid experimental screening and in-situ diffraction studies as a powerful strategy for novel compounds discovery. When applied for the previously “empty” Na-Zn-Bi system, such an approach led to 4 novel phases. The compositional space of this system was rapidly screened via the hydride route method and the theoretically predicted NaZnBi (PbClF type, P4/nmm) and Na11Zn2Bi5 (Na11Cd2Sb5 type, P-1) phases were successfully synthesized, while other computationally generated compounds on the list were rejected. In addition, single crystal X-ray diffraction studies of NaZnBi indicate minor deviations from the stoichiometric 1:1:1 molar ratio. As a result, two isostructural (PbClF type, P4/nmm) Zn-deficient phases with similar compositions, but distinctly different unit cell parameters were discovered. The vacancies on Zn sites and unit cell expansion were rationalized from bonding analysis using electronic structure calculations on stoichiometric “NaZnBi”. In-situ synchrotron powder X-ray diffraction studies shed light on complex equilibria in the Na-Zn-Bi system at elevated temperatures. In particular, the high-temperature polymorph HT-Na3Bi (BiF3 type, Fm-3m) was obtained as a product of Na11Zn2Bi5 decomposition above 611 K. HT-Na3Bi cannot be stabilized at room temperature by quenching, and this type of structure was earlier observed in the high-pressure polymorph HP-Na3Bi above 0.5 GPa. The aforementioned approach of predictive synthesis can be extended to other multinary systems