Figure 2

Powder XRD measurements. (a) pXRD patterns for Co _x Fe_1−xS₂ NCs, with x = 0.0, 0.125, 0.25, 0.375, 0.5, 0.625, 0.75, 0.875, and 1.0. The plots for different composition (x) are y-offset for clarity. The reference pXRD patterns of cattierite (CoS₂: PDF 00-041-1471) and iron pyrite (FeS₂: PDF 00-042-1340) are shown below without an offset. The dashed vertical lines indicate the positions of the FeS₂ 200, 210, 220, and 311 reflections. (b) Extracted cubic lattice constants for the different samples. Vertical error bars denote the uncertainty in the Rietveld fits to a cubic pyrite structure. The horizontal error bars indicate the compositional deviations following the Vegard’s law from the nominal ones. (c) Plots of crystallite size versus x as estimated from the Rietveld refinements of the XRD patterns corresponding to the 200, 220, and 311 reflections.