Low-T ferroelectricity in antiphase domain boundaries of SrTiO3

The ferroelectric transition of bulk strontium titanate is suppressed by a combination of two effects: (1) the structural changes produced by the antiferrodistortive transition at T-a =105 K and (2) the quantum fluctuations. The structural changes are strongly perturbed within antiphase domain boundaries , and this in such a manner that a ferroelectric transition should occur in boundaries containing the tetragonal c-axis at T-c similar to 35 to 40 K. This provides a possible explanation for a number of anomalies observed in SrTiO3 at those temperatures. We report a new low-T anomaly on the lattice parameter c measured on a thin polished platelet. The above model is consistent with its sign and size, as well as with the sign and size of earlier birefringence measurements on similar samples.