Low temperature structural transformations on the (001) surface of SrTiO3 single crystals

The smooth (001) surfaces of SrTiO₃(STO) single crystals were investigated by the reflection high-energy elec-tron diffraction method in the temperature range from 5.5 to 300 K. The Raman scattering confirmed the high quali-ty of STO samples. Five structural anomalies were found depending on temperature. The antiferrodistortive phase transition from the cubic structure to tetragonal, observed in the STO bulk at 105 K, on the surface extends from 70 to 120 K. The anomalies below 7 K and about 35 K are similar to those in the bulk considered as a crossover be-tween the growth of the ferroelectric atomic displacements with decreasing temperature and quantum-mechanical stabilization of this growth due to the zero-point atomic motion. The other two anomalies are related only to a sur-face. Differentiation of lattice parameters depending on the depth from a surface revealed nonmonotonic changes, which could be used for detecting the structural transformations. The comprehensive understanding of the structural properties of ABO₃perovskite surfaces is important for elucidating the nature of the effects at the boundary of me-tallic ferromagnetism in similar materials.