Approximants C4 and C5 of the Decagonal Quasicrystal in Al70Co15Ni10Tb5 Alloy Obtained by Quenching from Melting State under High Static Pressure

Two new approximants of the decagonal quasicrystal were found in the Al70Co15Ni10Tb5 alloy, which was prepared by quenching from melting state under high static pressure (7.0 GPa). The lattice parameters of the approximants were =1.38 nm, b=1.6 nm, c=2.0 nm (C4, B-type orthorhombic crystalline phase); =1.20 nm, b=1.60 nm, c= 2.30 nm (C5, P-type orthorhombic crystalline phase), respectively. They were also studied by means of high-resolution electron microscopy (HREM). It was found that there was a close relationship between them. The HREM pattern can be regarded as an ordered one of Penrose tiling.