Nature of the Incommensurate Phase of Rb2ZnCl4
Rb2ZnCl 4 is one of the many numbers of isomorphous compounds of the form A2BX4(A = K, Rb etc., B = Se, Zn etc., X = O, Cl, Br etc.) which undergo a continuous transition from a normal (N) phase (space group Pmcn) at a temperature Tc to a one dimensionally modulated incommensurate (IC) phase (see e.g. Iizumi et al 1977, de Pater and van Dijk 1978) characterised by a distortion with a periodicity that is an irrational fraction of the periodicity of the underlying lattice. The modulation wavevector of the incommensurate distortion, referred to the unit cell of the N phase, is given by q s = (1/3 - δ)C* where c is the pseudo-hexagonal axis. In Rb2ZnCl 4 δ ~ .029 just below Tc ~303 K (Mashiyama et al 1982) decreasing monotonically to zero at TL ~ 190 K where the IC phase locks into a commensurate (C) ferroelectric phase (p2lcn).
KeywordsAcoustic Mode Diffuse Scattering Incommensurate Phase Satellite Reflection Primary Satellite
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