Abstract
Abstract High‐resolution X-ray scattering measurements of the antiferrodistortive phase transitions in the perovskites SrTiO3, RbCaF3 and KMnF3 have recently revealed the existence of two length scales in the critical scattering above Te . Here we review these observations and discuss how they might be related to the well known existence of two time scales (the "central peak" problem) in the critical dynamic response function above Te . We reach the tentative conclusion that within a few degrees of Te both the time and length scales of the fluctuations are strongly influenced by defects and that the intrinsic critical behaviour is swamped by these effects in most crystals.
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