Neutron diffuse scattering in the disordered phase of CrBr₄. I. Experimental. Elastic and quasi-elastic coherent scattering in single crystals

Experimental results on elastic neutron diffraction and diffuse scattering in the plastic phase CrBr 4 (T>320K) are reported. A new determination of the structure in this phase is made from 30 independent reflections. Intense diffuse scattering is observed as anisotropically distributed in the vicinity of the (220) Bragg peak. It is shown that this diffuse scattering is due to orientational correlations. No critical behaviour of the intensity is observed at T=T c . Inelastic analysis of the diffuse scattering indicates the existence of three quasi-elastic components with HWHM of 0.03, 0.25 and 0.5 THz respectively.