The Superstructures of Iron Selenide Fe₇Se₈

Abstract

Iron vacancies in Fe 7 Se 8 are confined to the alternate iron layers parallel to the c plane of the fundamental lattice with the NiAs structure. The origin of the ferrimagnetisni of Fe 7 Se 8 ( T c =187°C) may be attributed to this ordered arrangement similarly to the case of Fe 7 Se 8 . There are two types of the superstructure: low- and high-temperature ones. The unit cell dimensions and the lattice symmetries of these structures are as follows: