![Sample our Earth Sciences journals, sign in here to start your access, latest two full volumes FREE to you for 14 days]({"type":"image" , "src" : "/sda/5930/TOC-Subject-Sample-2021-Earth-Sciences.jpg"})
Abstract
The second-order phase transition at 265 K in the triammonium hydrogen disulfate compound (NH4)3H(SO4)2 has been observed by X-ray diffractometry. The space group below 265 K is identified to be P2/b. The recorded X-ray diagrams show a doubling of the primitive unit cell. The observed symmetry change has been described by the Landau theory of continuous phase transitions. The implied high-symmetry point of the corresponding first Brillouin zone shows other possible space groups for the low-temperature structure which are in agreement with Landau and Lifshitz criteria.
All the theoretical results are discussed and compared with the obtained space group.
Key Words: