Commensurate-incommensurate transition inK2SeO4: X-ray scattering

We report an energy-dispersive x-ray-diffraction study of the commensurate-incommensurate transition and the incommensurate phase of ${\mathrm{K}}_2$Se${\mathrm{O}}_4$. Supercooling effects are observed together with thermal hysteresis over a broad temperature range. The deviation from commensurability, $\delta$, is a function of distance away from the surface. The x-ray results imply a long healing length for the order parameter, of the order of several micrometers.