In Situ X-ray Diffraction Study of the Formation of Fe(Se,Te) from Various Precursors

The formation of the FeSe0.5Te0.5 phase was studied by means of high energy synchrotron x-ray diffraction. The precursors consisted of Fe, Se and Te or Se0.5Te0.5 powder mixtures and were encased in a metal (Cu/Nb) composite sheath to prevent evaporation of Se and Te during high temperature processing.

In all cases (Fe – Se – Te ternary mixture; Fe - Se0.5Te0.5 binary mixtures with two different Fe particle sizes) the ternary alloy forms via Fe(Se,Te)2 and Fe3(Se,Te)4 intermediate phases. When unreacted Se and Te powders are used in the precursor, partial Se1-xTex alloying takes place during heating prior and during the formation of the intermediate phases.

As the alloying is incomplete, the resulting Fe(Se,Te) phase is not homogeneous. Using pre-alloyed Se0.5Te0.5 allows a better control of the reaction although homogeneisation also occurs in the Fe(Se,Te) phase as a consequence of the phase equilibria of the Se – Te system. The grain size of the starting Fe powder has no influence on the reaction path for the grain sizes used in the present study.

However, the reaction rate for Fe(Se,Te) formation is clearly sensitive to this parameter.