A single crystal X-ray and HRTEM study of new series of compounds DyCux (x=4.5, 4 and 3.5)

A series of monoclinic compounds DyCu_x (x=4.5,4 and 3.5) is described. It is constructed from structural blocks AB₅ (cubic AuBe₅ structure type) and AB₂ (cubic MgCu₂ structure type) by stacking nAB₅+AB₂ and giving the compositions A₂B₇,AB₄,A₄B₁₇,A₅B₂₂,A₆B₂₇,…,AB₅. The resulting monoclinic superstructures can be derived from the cubic AuBe₅ type by introducing planar defects parallel to {hhh} that lead to a nearly orthogonal ≈(n+2)×(n+2)×(n+2−0.5) supercells. The present series is analogous to the monoclinic-hexagonal-trigonal-orthorhombic series A_n+1B_5n+2 obtained by the stacking (n-1)AB₅+A₂B₇ where AB₅ is of the hexagonal CaCu₅ structure type and A₂B₇ is of the monoclinic Zr₂Ni₇ structure type.