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Abstract: Changes in structure and dielectric properties at elevated temperatures have been investigated on single-crystals of sodium potassium niobate, Na0.5K0.5NbO3, grown by the flux method. Single-crystal X-ray diffraction studies revealed that the crystals underwent orthorhombic–tetragonal and tetragonal–cubic phase transitions at 465 and 671K during heating and 446 and 666K during cooling, respectively. Both transitions were accompanied by volumetric discontinuities of collapse upon heating and expansion upon cooling, suggesting that the transitions were of the first order. The coordination numbers of an Nb showed a decreasing tendency with decreasing temperature, i.e., 6 in cubic, 5+1 in tetragonal and 4+2 in orthorhombic. An Na atom occupied a slightly different position from the K atom in 12-fold coordination, resulting in fewer coordination numbers of 8+4 in cubic and tetragonal and 7+5 in orthorhombic. The spontaneous polarisation (P s) estimated from the atom positions and formal charges were approximately 0.29Cm−2 in orthorhombic and 0.18Cm−2 in tetragonal. The contribution of the alkaline oxide components to P s was estimated to be approximately 15% in both ferroelectric forms. The temperature-induced transitions were also confirmed through the dielectric constant and dielectric loss at various frequencies and the differential scanning calorimetry. [ABSTRACT FROM AUTHOR]

The article presents information on the crystal structure of the compound trigadolinium ruthenium heptaoxide or Gd3RuO7. The structure is composed of infinite single chains of corner-linked [RuO6] octahedra embedded in the [Gd3O] matrix. The octahedra in the P21nb modification have two tilt systems about the a and c axes. The title compound contains six crystallographically independent Gd atoms coordinated by seven O atoms each, with interatomic distances ranging from 2.190 (13) to 2.605 (13) Å.

Presents a study which measured the structure factors for two compositions of garnets using focused synchrotron X-radiation. Difference electron density maps; Effectivenes in chemical bonding; Relative position of the rara-earth atoms in the periodic table.

The flux-grown single crystals of tridysprosium ruthenium heptaoxide, Dy3RuO7, have a noncentrosymmetric orthorhombic structure composed of infinite single chains of corner-linked RuO6 octahedra embedded in a Dy3O matrix. Partial disorder of Dy atoms was faintly observed. Two Dy atom sites out of the six crystallographically independent Dy sites split into two positions, which are separated by approximately 0.3–0.5 Å and have different coordination environments. The investigated crystal was an inversion twin. [ABSTRACT FROM AUTHOR]

The room-temperature structure of potassium titanyl phosphate (KTiOPO4, KTP) with Pna21 symmetry has been studied by means of synchrotron radiation. Each of the two crystallographically unique K1 and K2 cations is split over two sites that are shifted along the c direction by 0.287 (13) and 0.255 (13) Å for the K1 a/ b and K2 a/ b pairs, respectively. The refined populations of the minor K1 b and K2 b sites are 0.102 (12) and 0.132 (17), respectively. It is shown that accurate high-resolution synchrotron data ( Rmerged = 0.015 for 25 010 reflections, 9456 unique, sinθ/λ limit > 1.0) are required for the determination of a reliable structure model. [ABSTRACT FROM AUTHOR]