High-order diffraction satellites in Rb2ZnCl4: Experimental evidence against overall phason thermal factors

¹ Departamento de Física Aplicada I, Escuela Técnica Superior de Ingenieros, Industriales y de Telecomunicación, Universidad del País Vasco, Alameda de Urquijo s/n, 48013 Bilbao, Spain
² Departamento de Física de la Materia Condensada, Facultad de Ciencias Universidad del País Vasco - Apdo. 644, 48080 Bilbao, Spain
³ Laboratoire de Chimie-Physique du Solide (UA 453), Ecole Centrale - 92295 Châtenay-Malabry-Cédex, France
⁴ Departamento de Física Aplicada II, Facultad de Ciencias, Universidad del País Vasco - Apdo. 644, 48080 Bilbao, Spain

Received: 5 August 1996
Accepted: 21 October 1996

Abstract

The temperature dependence of the diffraction pattern in the in com men su ra te phase of can be explained by the temperature variation of 3 structural parameters: the amplitude of the primary mode of symmetry, the soliton density defining its anharmonicity, and the amplitude of a third harmonic modulation. The addition of overall phason thermal factors is shown to be inconsistent with the experimental data which include fifth- and seventh-order satellites. It is further demonstrated that the use, in conventional structural analysis, of an incomplete structural model with null or small anharmonicity, together with a reduced dataset lacking higher-order weak satellites, may lead to the successful refinement of a phason thermal factor, which has a spurious character.