Direct observation of the intergrown α-phase in β-TmAlB4 via high-resolution electron microscopy

A TmAlB4 crystal with a ThMoB4-type (β-type) structure phase related to a hexagonal AlB2-type structure was studied by electron diffraction and high-resolution electron microscopy. A high-resolution image clearly exhibits an intergrown lamellar structure of a YCrB4-type (α-type) phase in the matrix of the β-type phase in TmAlB4 crystal. The lamellar structure can be characterized by a tiling of deformed hexagons, which are a common structure unit in the α-type and β-type structures. The intergrown nanostructure is considered to be attributed to the origin of low temperature anomalies in physical properties.