Showing papers by "J. Paul Attfield published in 1992"

Order and disorder of vanadyl chains: crystal structures of vanadyl dihydrogen arsenate (VO(H2AsO4)2) and the lithium derivative Li4VO(AsO4)2

Abstract: The crystal structure of layered, tetragonal VO(H 2 AsO 4 ) 2 (a=9.1305 (1) A, c=8.1318 (2) A) has been refined in space group I4/mcm from laboratory X-ray powder diffraction data by the Rietveld method, giving R wp =10.1% and R F =5.5%. Disorder of the vanadium atoms over two sites results from infinite .V=O...V=O. chains orienting in the ±c-directions at random, due to the flexibility of the arsenate groups that link neighboring chains

Magnetic structures of MnPO4·D2O and MnAsO4·D2O from time-of-flight neutron powder diffraction data

Abstract: The magnetic properties of the isomorphous compounds MnXO4·D2O (X = P, As) have been investigated by magnetic-susceptibility and low-temperature time-of-flight neutron powder diffraction methods. These materials behave as Curie–Weiss paramagnets at high temperatures and order antiferromagnetically below Neel temperatures of 33 and 24 K for X = P and As, respectively. The 4 K magnetic structures of the two compounds have been determined from time-of-flight neutron powder diffraction and consist of antiferromagnetic Mn–O–Mn chains in the [101] direction with ordered magnetic moments of 3.52(5) and 3.54(5)µB, for X = P and As, parallel to [101]. The crystal structures have also been refined precisely from the same data, and the resulting bond distances and angles are used to rationalise the relative strengths of the interchain magnetic superexchange interactions.