Valery E. Zavodnik

The δ-phase of SrTeO3 at 780 K

As part of a structural investigation of strontium tellurate(IV) (STO), SrTeO3, with particular emphasis on the crystal chemistry and phase transitions, the structure of the δ-phase has been determined at 780 K using a single-crystal analysis. Both structural and non-linear optical measurements indicate that STO undergoes a γ→δ second-order ferroelectric phase transition at 633 K from the C2 (γ) to the C2/m (δ) modification. Systematic differences between the similar γ- and δ-phase structures were determined and it was found that this phase transformation can be described by a displacive mechanism.

The α-phase of SrTeO3 at 295 K

The crystal structure of strontium tellurite (STO), SrTeO3, has been determined at room temperature using X-ray diffraction data obtained from single crystals grown by the Czochralski method. Selection of a non-centrosymmetric (C2) structure model was confirmed by the second harmonic generation test. The structure of STO is built up of three types of distorted [SrOx] polyhedra (x = 6, 7 and 8) which share their oxygen anions with TeO3 pyramidal units. These main anionic polyhedra are responsible for establishing two types of tunnels required for the electron lone pairs of the Te4+ cation.

The γ-phase of SrTeO3 at 583 K

As a part of current systematic investigations of strontium tellurite, SrTeO3, with particular emphasis on crystal chemistry and phase transitions, the structure of the gamma phase has been determined at 583 K using a single-crystal analysis. Both structural and nonlinear optical measurements indicate a beta-gamma first-order phase transition temperature that is close to 563 K. The structure of the gamma phase is monoclinic (C2) and does not differ essentially from the alpha phase (C2). Comparison of the alpha and gamma structures shows that the main atomic shifts and tiltings are connected with Te4, Te5 and Te6 pyramids.