title: Vacancy-ordering effects in AlB2-type ErGe2 - x(0.4 < x < or = 0.5).
abstract: In the Er-Ge system, the compostion range ErGe(2) to Er(2)Ge(3) has been investigated. Eight samples were produced by arc melting of the elements, and analyzed using X-ray powder diffraction. Nine crystal structures were found to be present in the samples. The structures are described as a homologous series and presented within the superspace formalism using the superspace group X2/m(alpha0gamma)0s, X representing the centring vector ((1/2), (1/2), 0, (1/2)). In this description the modulation vector q = (alphaa* + gammac*) is shown to be a direct measure of the Ge content as ErGe(2 - alpha) (alpha falls in the range 1\over 3 to (1/2)). The large composition range is achieved by extended vacancy ordering in the planar 6(3) net of Ge with subsequent relaxation.
authors.affiliation: Inorganic Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden. jeppe@inorg.su.se
authors.forename: Jeppe
authors.initials: J
authors.lastname: Christensen
authors.forename: Sven
authors.initials: S
authors.lastname: Lidin
authors.forename: Bernard
authors.initials: B
authors.lastname: Malaman
authors.forename: Gerard
authors.initials: G
authors.lastname: Venturini