It has been pressumed that there are several polymorphs of CuFeS
2-X, i.e. tetraponal (α), cubic (β). another tetragonal (γ) and another cubic (fcc) phases. In order to esplaine these complicated relations, especially among tetragonal (α), cubic (β), and another cubic (fcc) phases, the authors had a dissociation experiment of the natural chalcopyrite CuFeS
2.
The puhrerised pure chalcopyrite (α) heated in the hydrogen-gas stream at the temperature between 300°-500°C for 10-900 minutes, were observed by x-ray diffraction and under the microscope, and their changes in weight and in PH
2S/PH
2 were measured. The experimental result showed that at the temperature of 400°-500°C, ordinary tetragonal chalcopyrite changed into the principally cubic phase (β) by desulfurization, whose x-ray powder pattem resembled to those of the “β” phase by Hiller and Probsthain (1956) or of the natural cubic chalcopyrite. This β-phase have a composition range of CuFeS
1.856_??_CuFeS
1.740 and their x-ray powder pattern, which has characteristic diffraction in 7.5 (110) and 3.7 (220) Å, can be indexed principally with bcc structure except some faint additional lines. With an increase in desulfurization, this β-phase continues to decrease their diffraction angles, until, with the escaping of 15% sulfur, the formation of bomite s. s. is seen beside the β-phase.
From the previous works by many investigators and the result in this experiment, it may be stated that the ordinary tetragonal chalcopyrite is not stable at the temperature above 550°C, and that the so-called cubic chalcopyrite (fcc), which would be stable at the high temperature, may be identified with β-phase prepared by the desulfurization of ordinary tetragonal chalcopyrite CuFeS
2 independently of temperature factor. Compositional range of this β-phase which contains less sulfur than stoichiometric CuFeS
2 may be included in the area of the chalcopyrite s.s. by Yund and Kullerud (1966) and of the intermediate s.s. by Merwin and Lombard (1937).
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