Low-energy structures of zinc borohydride Zn(BH$_4$)$_2$

TL;DR

This study systematically explores the low-energy structures of zinc borohydride, identifying a new stable phase and potential phase coexistence at ambient conditions, with implications for hydrogen storage applications.

Contribution

The paper discovers a new dynamically stable structure of zinc borohydride and analyzes phase stability and coexistence using computational methods.

Findings

Identified a new stable $I4_122$ structure for zinc borohydride.

Predicted low transition barriers indicating phase coexistence.

Simulated X-ray patterns match experimental samples.

Abstract

We present a systematic study of the low-energy structures of zinc borohydride, a crystalline material proposed for the hydrogen storage purpose. In addition to the previously proposed structures, many new low-energy structures of zinc borohydride are found by utilizing the minima-hopping method. We identify a new dynamically stable structure which belongs to the $I4_122$ space group as the most stable phase of zinc borohydride at low temperatures. A low transition barrier between $I4_122$ and $P1$, the two lowest-lying phases of zinc borohydride is predicted, implying that a coexistence of low-lying phases of zinc borohydride is possible at ambient conditions. An analysis based on the simulated X-ray diffraction pattern reveals that the $I4_122$ structure exhibits the same major features as the experimentally synthesized zinc borohydride samples.