Structure and thermal expansion of (Crx,V1−x)n+1AlCn phases measured by X-ray diffraction

MAX phases in the (Crx,V1−x)n+1AlCn system were synthesized by reactive sintering or hot isostatic pressing of elemental powders at temperatures between 1400 °C and 1600 °C. For n = 1, a complete range (0 ≤ x ≤ 1) of solid solutions was found; for n = 2 and 3 the solubility ranges were 0.25 ≤ x ≤ 0.75 and 0 ≤ x ≤ 0.5, respectively. Powder X-ray diffraction revealed that the lattice parameters of all (Crx,V1−x)n+1AlCn solid solutions followed Vegard's law. The thermal expansion coefficients of the various compounds were determined from Rietveld refinements of X-Ray patterns obtained at temperatures between ambient and 800 °C. For the n = 1 and 3 phases the thermal expansion coefficients were almost isotropic; those for the n = 2, however, were quite anisotropic with the expansion along the a-axis being significantly larger than along the c-axis. As a general trend, vanadium rich compounds have smaller thermal expansion coefficients than their Cr-rich counterparts.