Hetero-crystals, a new type of composite alloys: a case study of the 1144-phase TM-phosphides and -arsenides.*

The recently discovered 1144-phase [1-2] suggests a new type of composite alloys, namely hetero-crystals. The author will present its definition and demonstrate wide existence. The hetero-crystals consist of the layered skeleton and hetero-cations alternatively located on both sides of the skeleton. Tuning cation species leads to significant modifications to structures, granting an exceptional chance to manipulate the emerging phases. The 1144-phase is examined as a case study of hetero-crystals. Various 1144-arsenide and phosphides are examined by combining first principle calculation and ideal solution approximation, wherein configurational, vibrational and electronic degrees of freedom are fully considered. Remarkably, the seemingly random occurrence of the 1144 phases is governed by a rule that involves two factors: elastic distortion and charge balance. Derived from 1144-phosphides, the rule, nevertheless, is heuristic and generic, which leads to an outlook of other hetero-crystals promising to be stabilized. [1] B. Q. Song, et. al. Physical Review B 97 (9), 094105 (2018). [2] B. Q. Song, et. al. Physical Review Materials 2 (10), 104802 (2018)