Search

Ferroelectric domains in PbTiO3/SrTiO3 superlattices are studied using synchrotron x-ray diffraction. Macroscopic measurements reveal a change in the preferential domain wall orientation from {100} to {110} crystallographic planes with increasing temperature. The temperature range of this reorientation depends on the ferroelectric layer thickness and domain period. Using a nanofocused beam, local changes in the domain wall orientation within the buried ferroelectric layers are imaged, both in structurally uniform regions of the sample and near defect sites and argon ion-etched patterns. Domain walls are found to exhibit a preferential alignment with the straight edges of the etched patterns as well as with structural features associated with defect sites. The distribution of out-of-plane lattice parameters is mapped around one such feature, showing that it is accompanied by inhomogeneous strain and large strain gradients. [ABSTRACT FROM AUTHOR]

Single crystals of transition metal oxides forming the Ruddlesden–Popper series are necessary for complete studies of their often exciting physical properties. In the strontium titanate family, crystal growth of all compounds apart from SrTiO3 has been elusive so far. We have successfully grown crystals of the high-temperature polymorph of Sr2TiO4, by using a floating-zone melt growth followed by a rapid cooling procedure. We report the crystal structure of the new modification, which is isostructural to the orthorhombic Sr2VO4 and Sr2CrO4. This structure hosts an uncommon layered sub-lattice of TiO4 tetrahedra and transforms into the tetragonal low-temperature polymorph via a complex reconstructive transition. The transformation mechanism between the two phases was studied and explains the reasons for the unsuccessful growth of tetragonal Sr2TiO4. The orthorhombic Sr2TiO4 is an insulator, with a band gap of 3.9 eV. It has a large (≈40) dielectric constant, but despite its polar structure does not show any signatures of a ferroelectric order. [ABSTRACT FROM AUTHOR]