Crystal structures and phase stability in pseudobinary CaAl2−xZnx

Samples in the pseudobinary system CaAl2−xZnx   (0⩽x⩽20⩽x⩽2) were synthesised from the elements. Three different structure types, the C15 and C36 Laves phase structures and the KHg2 (CeCu2) structure, were observed. The structures and homogeneity ranges of the underlying phases were investigated by electron microscopy and thermal analysis as well as X-ray powder diffraction. The stability ranges for the different structure types were found to be 0⩽x⩽0.180⩽x⩽0.18, 0.28⩽x⩽0.680.28⩽x⩽0.68 and 0.93⩽x⩽20.93⩽x⩽2 for the C15, C36 and KHg2 structure types, respectively.

The investigation of the pseudobinary system CaAl2−xZnx yielded the structural sequence MgCu2 (C15)–MgNi2 (C36)–KHg2 with increasing x. The structural change C15→C36 between two Laves phase structures is induced by the decrease in valence electron concentration. However, with increasing Zn content the system becomes increasingly polar and at some point favours the more open packed KHg2 structure over a Laves phase structure.Figure optionsDownload as PowerPoint slide