Phason fluctuations in i-AlPdRe and i-CdYb phases

We present a high resolution X-ray diffraction study on two single grain phases: the i-AlPdRe phase which is supposed to be isostructural to the i-AlPdMn one and the new binary CdYb phase. Both the Bragg peak width (sensitive to uniform phason strain distribution) and the diffuse scattering (sensitive to long wavelength phason fluctuations) have been studied. In the i-AlPdRe phase, we find an anisotropic distribution of diffuse scattering intensity around the Bragg peaks. Its intensity is related to Q(per), demonstrating its relation to phason fluctuations. The amount of diffuse scattering is similar to what was previously found in the AlPdMn phase, but the shape anisotropy is markedly different. The i-CdYb phase presents a good structural quality. Its Bragg reflection shows an isotropic broadening which scales with Q(per), as a consequence of uniform phason strain distribution with a magnitude similar to what was found in the i-ZnMgRe phases. There is also a clear anisotropic distribution of diffuse scattering intensity located around the Bragg peaks. It is related to long wavelength phason fluctuations with an anisotropy pointing toward a threefold type instability. (C) 2002 Published by Elsevier Science B.V.