Miscibility between synthetic FeS and TiS: An insight into the phase relations in natural Ti-bearing iron monosulfides

Syntheses of (Fe,Ti)S analogs of natural Ti-bearing troilites were performed in evacuated and sealed silica glass tubes to investigate the extent of the knowledge on the solid solution between FeS and TiS. The synthesized (Fe,Ti)S phases were investigated using electron probe microanalysis and powder X-ray diffraction. The synthetic phases of the (Fe,Ti) S series adopt NiAs-type structure of P63/mmc space group in the compositional range from FeS to Fe0.5Ti0.5S. Members of the series rich in titanium crystallize in the R-3m space group. The stoichiometric TiS can adopt both structure types. Some additional diffraction peaks were observed in numerous samples. However, due to the insufficient quality of powder XRD data, crystal structure parameters of only samples with troilite 2C superstructure could be successfully refined. Systematic variation of deficit in metal (Me = Fe + Ti) site occupancy with titanium content was observed in the synthetic samples. This deficit increases with the increasing Ti content in a compositional range from pure FeS to Fe0.2Ti0.8S. In samples containing more titanium than this composition, the deficit of the metal site occupancy decreases, and the composition of end-member TiS is very close to the ideal stoichiometry.