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The Reconstructive Phase Transformation β‐Co 2 P → α‐Co 2 P and the Structure of the High‐Temperature Phosphide β‐Co 2 P
Author(s) -
Ellner M.,
Mittemeijer E. J.
Publication year - 2001
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/1521-3749(200109)627:9<2257::aid-zaac2257>3.0.co;2-w
Subject(s) - phosphide , melting point , phase (matter) , materials science , crystallography , chemistry , differential thermal analysis , atmospheric temperature range , metal , metallurgy , diffraction , thermodynamics , organic chemistry , physics , optics
Metallographical and differential thermoanalytical (DTA) investigatitons indicate that the well known phosphide Co 2 P (Pearson code oP 12, space group Pnma , Co 2 Si type) is not stable up to the melting point, T = 1659 K; it is therefore designated as the low‐temperature phase α‐Co 2 P. In the temperature range from 1428 to 1659 K, another, high‐temperature phase, designated as β‐Co 2 P, exists. X‐ray powder diffraction investigation of liquid quenched alloys in the composition range x P = 0.25 to 0.335, with x P as the mole fraction, show that the high‐temperature phase β‐Co 2 P is isotypic with Fe 2 P ( hP 9, P 6 2 m ). For the ideal composition Co 2 P, the unit cell parameters are: a = 5.742(2) Å, c = 3.457(5) Å, c / a = 0.621. Among the binary transition metal‐containing phosphides and arsenides isotypic with Fe 2 P, β‐Co 2 P is the only known high‐temperature phase and it shows (i) the highest axial ratio c / a and (ii) the “smallest” distortion of the hcp substructure formed by the transition metals atoms in the Fe 2 P structure type.