White beam X-ray topographic measurement of spontaneous strain in strontium titanate

We have measured the spontaneous strain of a zone boundary mode phase transition in strontium titanate by using the X-ray topographic contrast produced by the lamellar domain structure. The hill and valley structure of the lattice planes intersecting the domain walls leads to the orientation contrast consisting of pairs of a bright stripe and a dark stripe. The linear relation between the splitting of the pairing stripes and a camera distance gives the temperature dependence of the spontaneous strain, which is in the order of 10-4 at 4.8 K, as well as the critical index of order parameter β = 0.32