The structure of CuGeO 3 has been analyzed by means of x-ray and neutron single-crystal diffraction as a function of temperature. There is a pronounced temperature dependency of the atomic positions in the hightemperature Pbmm phase. The observed deformation scheme on cooling from 295 to 20 K may be characterized by a rotation of the Cu͓O͑2͔͒ 2 ribbons around the c axis. It is related to the distortion below the spin-Peierls transition, and has an impact on the magnetic interaction parameter J. For the distorted structure in the spin-Peierls phase, based on a large set of superstructure reflections, we qualitatively confirm the proposed model ͑space group Bbcm͒ with a slightly different direction of the oxygen displacements. A computation of J reveals that its splitting in the spin-Peierls phase is dominated by the modulation of the Cu-O-Cu bond angle.

The development of multidetectors for use in X‐ray and neutron scattering experiments has created an interest in methods for integrating Bragg peaks in three‐dimensional data arrays representing intensity scattered from single crystals. A method of using a priori information, extracted from the strongest peaks, to obtain statistically optimum results has been developed at the Institut Laue–Langevin (ILL), Grenoble. The method is outlined in this paper and results of its application to neutron diffraction are discussed.

The magnetic properties and magnetic structure are presented for CoPS, a quasi-two-dimensional antiferromagnet on a honeycomb lattice with a Néel temperature of [Formula: see text] K. The compound is shown to have XY-like anisotropy in its susceptibility, and the anisotropy is analysed to extract crystal field parameters. For temperatures between 2 K and 300 K, no phase transitions were observed in the field-dependent magnetization up to 10 Tesla. Single-crystal neutron diffraction shows that the magnetic propagation vector is k  =  [Formula: see text] with the moments mostly along the [Formula: see text] axis and with a small component along the [Formula: see text] axis, which largely verifies the previously-published magnetic structure for this compound. The magnetic Bragg peak intensity decreases with increasing temperature as a power law with exponent [Formula: see text] for [Formula: see text].

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