As2O3 Polymorphs: Theoretical Insight into Their Stability and Ammonia Templated Claudetite II Crystallization

An original room-temperature and ambient-pressure method of claudetite II crystallization consisting in ammonium arsenate­(III) decomposition is presented. Claudetite II is characterized by single crystal and powder X-ray diffraction, Raman spectroscopy and differential scanning calorimetry. Claudetite I and II equations of state were obtained by DFT calculations of their energies incorporating dispersive contribution accounted for by the Grimme method. It has been shown that claudetite II is metastable in the investigated pressure range and a new high-pressure As2O3 polymorph has been predicted. Presented computational results indicate that the contribution of van der Waals interactions to the systems’ energy cannot be neglected.