A high-resolution electron microscopy study of the domain structures of monoclinic τ²-AL₁₃CO₄

Abstract

A high-resolution electron microscopy investigation was carried out to study the domain structure of monoclinic τ²-Al₁₃CO₄ whose β≈ 108° and parameters a and c are ≈²SS 2·618 … times, where τ= (1 +√5)/2 is the golden number, greater than their counterparts in Al₁₃Co₄ (a= 1·5184nm, b= 0·8122nm, c= 1·2340nm, β= 107·90°). Co atoms in the (010) layer form pentagons and 36° rhombi with an edge length of 1·23 nm. Different tessellations of these pentagons form various domain structures, such as parallel domains with the domain boundary parallel to (100), (201), (101) and (001) and 36° rotational domains (glide twins) with the domain boundary on (100) and (201). Various complex domain structures resulting from a combination of parallel and rotational domains have also been found, and, in addition to pentagons and 36° rhombi, other Penrose tiles such as 72° rhombus, ‘boat’, and ‘star’ also occur.