The absence of a discommensuration lattice in the incommensurate phase of Rb2ZnCl4

X-ray scattering close to the lock-in temperature T-L has been measured as a function of temperature to investigate whether the discommensuration latt ice is a useful description of the structure of Rb2ZnCl4. We review differe nt models for the incommensurate structure and discuss how they might be di stinguished by a scattering experiment. Our results are compared with earli er published x-ray measurements and with those obtained from nuclear spin-r esonance techniques. All of the x-ray results suggest that higher harmonics of the scattering measured in the a*/c* and b*/c* planes are much weaker t han predicted by the abrupt-discommensuration model. We conclude from the m easurements that this theory does not provide an adequate description of th e experimental results close to the lock-in transition.