Abstract
We present the results of a transmission electron microscopy study of an Al-Mn-Pd orthorhombic crystalline approximant to the decagonal phase that is isostructural to Al11Mn4. Selected area diffraction (SAD) and convergent beam electron diffraction (CBED) are discussed. The stereographic projection of the CBED Kikuchi bands is presented. While this phase exhibits a symmetry similar to the decagonal phase in the same alloy, the decagonal symmetry is broken by a splitting of some prominent Kikuchi bands. The intensity modulations of the SAD patterns strongly resemble those found in the 12 Å periodic Al-Mn and Al-Mn-Pd decagonal phases. These observations suggest the existence of clusters of atoms with a distorted icosahedral symmetry within the crystallographic unit cells. Most importantly, these distortions are consistent with the cluster distortions present in the Al-Mn and Al-Mn-Pd decagonal phases.