Chemically driven phason disorder in icosahedral Al-Pd-Mn alloys

A very strong composition dependence of linewidths and chemical order is seen in rapidly quenched i-Al90-xPdxMn10 and i-Al70PdxMn30-x alloys. The i-Al70Pd20Mn10 exhibits a very small residual peak width, with a half width at half maximum of 2.5×10-3 Ai-1. The replacement of Pd with Al drastically increases the peak widths, in particular the dependence on the phason momentum, G, by 2 orders of magnitudes, while little line broadening is seen when Mn replaces Pd. Concurrent with the line broadening, the chemically ordered face-centered icosahedral structure in Al70Pd20Mn10 transforms to the simple structure of Al80Pd10Mn10.