Eleven samples of nominal composition Mg2.2Si0.9925−x Sn x Sb0.0075 with x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.9925 were prepared by induction melting, ball milling, and spark plasma sintering. Hall effect, resistivity, Seebeck coefficient, and thermal conductivity measurements were conducted from room temperature to 400°C. Six of the samples were investigated for thermal stability by measuring powder x-ray diffraction while heating to 400°C. All samples were stable in air during the ∼12-h-long data collection, except for Mg2.2Sn0.9925Sb0.0075, which showed development of an elemental Sn phase after heating. The lattice parameter of each sample was extracted through Rietveld refinement and revealed a linear dependency on nominal composition. Measurement of top and bottom of the pellets exhibited systematic differences in lattice parameter and Seebeck coefficient, indicating that stoichiometry gradients are created during sintering.