Publication Date:
2018-03-06
Description:
Possible topologies of miscibility gaps in arsenian (Cu,Ag) 10 (Fe,Zn) 2 (Sb,As) 4 S 13 fahlores are examined. These topologies are based on a thermodynamic model for fahlores whose calibration has been verified for (Cu,Ag) 10 (Fe,Zn) 2 Sb 4 S 13 fahlores, and conform with experimental constraints on the incompatibility between As and Ag in (Cu,Ag) 10 (Fe,Zn) 2 (Sb,As) 4 S 13 fahlores, and with experimental and natural constraints on the incompatibility between As and Zn and the nonideality of the As for Sb substitution in Cu 10 (Fe,Zn) 2 (Sb,As) 4 S 13 fahlores. It is inferred that miscibility gaps in (Cu,Ag) 10 (Fe,Zn) 2 As 4 S 13 fahlores have critical temperatures several °C below those established for their Sb counterparts (170 to 185°C). Depending on the structural role of Ag in arsenian fahlores, critical temperatures for (Cu,Ag) 10 (Fe,Zn) 2 (Sb,As) 4 S 13 fahlores may vary from comparable to those inferred for (Cu,Ag) 10 (Fe,Zn) 2 As 4 S 13 fahlores, if the As for Sb substitution stabilizes Ag in tetrahedral metal sites, to temperatures approaching 370°C, if the As for Sb substitution results in an increase in the site preference of Ag for trigonal-planar metal sites. The latter topology is more likely based on comparison of calculated miscibility gaps with compositions of fahlores from nature exhibiting the greatest departure from the Cu 10 (Fe,Zn) 2 (Sb,As) 4 S 13 and (Cu,Ag) 10 (Fe,Zn) 2 Sb 4 S 13 planes of the (Cu,Ag) 10 (Fe,Zn) 2 (Sb,As) 4 S 13 fahlore cube.
Print ISSN:
0869-5911
Electronic ISSN:
1556-2085
Topics:
Geosciences
