NiAsStype
NiAs-type refers to a hexagonal crystal structure adopted by a group of binary compounds, commonly described using the prototype nickel arsenide, NiAs. The structure is hexagonal close-packed–derived and belongs to the space group P6_3/mmc (No. 194). In this arrangement, arsenic atoms form a close-packed sublattice, while metal atoms occupy all octahedral sites formed by the arsenic lattice. Each metal atom is sixfold coordinated by arsenic, and each arsenic atom is sixfold coordinated by metal, yielding a densely packed, ordered framework. The structure features alternating layers of metal and pnictogen (or chalcogen) along the c-axis, and is often discussed in terms of an ideal hexagonal close-packed geometry with a characteristic c/a ratio near 1.60, though real materials exhibit variations.
Occurrence and examples include numerous transition-metal pnictides, especially MnAs, FeAs, CoAs, and NiAs itself. The NiAs-type
Physical properties are typically metallic, with electrical conductivity resembling that of metals and a range of
In synthesis and analysis, NiAs-type materials are usually prepared by high-temperature solid-state reactions or direct combination