Core level photoemission spectroscopy and chemical bonding in Sr2Ta2O7.

Electronic parameters of constituent element core levels of strontium pyrotantalate (Sr2Ta2O7) were measured with X-ray photoelectron spectroscopy (XPS). The Sr2Ta2O7 powder sample was synthesized using standard solid state method. The valence electron transfer on the formation of the Sr–O and Ta–O bonds was characterized by the binding energy differences between the O 1s and cation core levels, Δ(O–Sr) = BE(O 1s) − BE(Sr 3d5/2) and Δ(O–Ta) = BE(O 1s) − BE(Ta 4f7/2). The chemical bonding effects were considered on the basis of our XPS results for Sr2Ta2O7 and earlier published structural and XPS data for other Sr- and Ta-containing oxide compounds. The new data point for Sr2Ta2O7 is consistent with the previously derived relationship for a set of Sr-bearing oxides. The binding energy difference Δ(O–Sr) was found to decrease with increasing bond distance L(Sr–O). © 2009, Elsevier Ltd

A comparative analysis of Rb : KTP and Cs : KTP optical waveguides

Planar optical waveguides were produced by exchange of Rb+ (Cs+) for K+ of Z-cut KTiOPO4 (KTP). The results of a systematic study of Rb:KTP and Cs:KTP waveguides obtained by combining measurements of the mode propagation constants, optical profiles and Raman scattering spectra are reported. The analysis of the refractive index profiles has shown that there is an exponential Rb+ (Cs+) distribution in the exchanged layers. Some dependences of the waveguide characteristics on the fabrication conditions are presented. Micro-Raman spectra have revealed a notable difference compared with the spectra of pure KTP in the range of external lattice modes as well as in the range of torsional vibrations of TiO6 octahedra. The exchanged layers exhibit lower perfection of the crystal lattice than that of pure KTP and effects of symmetry changes

Crystal growth and electronic structure of low-temperature phase SrMgF4

Using the vertical Bridgman method, the single crystal of low temperature phase SrMgF4 is obtained. The crystal is in a very good optical quality with the size of 10×7×5 mm3. Detailed photoemission spectra of the element core levels are determined by a monochromatic AlKa (1486.6 eV) X-ray source. Moreover, the first-principles calculations are performed to investigate the electronic structure of SrMgF4. A good agreement between experimental and calculated results is achieved. It is demonstrated that almost all the electronic orbitals are strongly localized and the hybridization with the others is very small, but the Mg–F bonds covalency is relatively stronger than that of Sr–F bonds. © 2015 Elsevier B.V