ANOMALOUS ELECTRICAL RESISTIVITIES OF DECAGONAL APPROXIMANTS

We present transport studies of decagonal approximants Al3Mn, Al13Fe4, and Al13Co4. Our results indicate that their transport properties, especially along the pseudo-quasi-periodic planes, strongly depend on the structure of the compounds. Monoclinic Al13Fe4 and orthorhombic Al13Co4 show anisotropic rho (T) dependence with metallic resistivity along the crystal axis (b axis) and nonmetallic resistivity along pseudo-quasi-periodic planes. The degree of anisotropy varies from several tens for orthorhombic Al13Co4 to several hundreds for Al13Fe4 which is anomalous for intermetallic compounds. Al3Mn shows anisotropic nonmetallic resistivity and, along the b axis, insulating behavior is indicated. In contrast, a monoclinic variant of Al13Co4 exhibits isotropic metallic transport properties. The variety of electronic states and the anomalous resistivity behavior observed are discussed in light of band-structure effects.