SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF A NEW ALLOTROPIC TYPE OFFERHP

We report on the synthesis and the structural characterisation of a ne w allotropic type of the ternary phosphide FeRhP. This new phase forms irreversibly when the high-temperature Fe2P-type allotropic type, ret ained at room temperature by rapid quenching from 1323 K to 273 K, is annealed at temperatures above 500 K. This new type decomposes irrever sibly at 760 K. Its crystal structure has been determined from single- crystal X-ray diffraction data. It is a new superstructure of the Fe2P -type, hexagonal, space group P (6) over bar 2m, with a = 11.882(2) An gstrom, c = 3.599(1) Angstrom, Z = 12. This phase is isotypic with FeP dP and with the low-temperature alpha-Co2As type. Most metal sites exh ibit iron / rhodium disorder, but a high rhodium concentration around selected phosphorus sites.