Original paper

The Cu-Bi-Se phase system at temperatures between 300 and 750C

Karup-Mø ller, S.


Phase relations were determined in the Cu-Bi-Se phase system at 300, 350, 400, 450, 550, 650 and 750°C. Four ternary phases, phase A-D, have been synthesized. Phase A (Cu4Bi4Se9) is isotype with Cu4Bi4S9, and phase B (Cu1.7Bi4.7Se8) and phase C (Cu3Bi5Se9) have the same structure type as 3P and 4P respectively of the pavonite homologous series. Phase D (Cu3Bi2Se6) was present in insufficient amount for x-ray-crystallographic studies. Apparently no sulphide corresponding to phase D exists. Phase A is stable up to 447°C. Phase B is stable at all temperature levels up to 550°C. Phase C has only been synthesized at 450°C. At 440°C it is not present. Phase D is stable at 300 and 350°C. Phase A displays no detectable variance in chemical composition. Maximum range in chemical composition of phase B was recorded at 450°C. At this temperature the compositional field of the phase is triangular in shape, defined by the compositions Cu8.8Bi34. Se56.5, Cu12.3Bi32.0Se55.7 7 and Cu13.4Bi31.9Se54.7. Phase C varies in composition between Cu16.2Bi30.3Se53.5 and Cu14.8Bi31.1 Se54.1 and phase D at 350°C between Cu28.8Bi17.1 Se54.1 and Cu26.0Bi18.7Se55.3. On the Cu-Se join Cu, CuSe, Cu2Se and Se dissolve negligible amounts of Bi, whereas substantial amounts of this metal may dissolve in Cu2-xSe. At 450 °C it may reach the composition Cu0.99Bi0.35Se1.00. On the Bi-Se join two intermediate phases are present, Bi2Se3 and BixSey. The former has near stoichiometric composition, dissolving max 0.8 wt.% Cu. BixSey displays a considerable variance in chemical composition and may dissolve up to 1wt.% Cu. With increasing temperature a liquid field projects from the Bi corner into the phase diagram. At 400 °C a small liquid field has developed around Cu35Bi10Se55. At 550 °C the two liquid fields present at 400 and 450 °C have merged into one field stretching from the bismuth corner of the phase diagram onto the Cu-Se join.