V. V. Atuchin

ELECTRONIC AND STRUCTURAL PARAMETERS OF PHOSPHORUS–OXYGEN BONDS IN INORGANIC PHOSPHATE CRYSTALS

Wide set of experimental results on binding energy of photoelectrons emitted from P 2p, P 2s, and O 1s core levels has been observed for inorganic phosphate crystals and the parameters were compared using energy differences Δ(O 1s - P 2p) and Δ (O 1s - P 2s) as most robust characteristics. Linear dependence of the binding energy difference on mean chemical bond length L(P–O) between phosphorus and oxygen atoms has been found. The functions are of the forms: Δ (O 1s - P 2p) (eV) = 375.54 + 0.146 · L(P–O) (pm) and Δ (O 1s - P 2s) (eV) = 320.77 + 0.129 · L(P–O) (pm). The dependencies are general for inorganic phosphates and may be used in quantitative component analysis of X-ray photoemission spectra of complex oxide compounds including functional groups with different coordination of P and O atoms.

Superstructure formation and X-ray photoemission properties of the TlTiOPO4 surface

X-ray photoemission spectroscopy (XPS) measurements have been executed for TlTiOPO4 to elucidate the general features in the electronic structure of the KTiOPO4 family compounds. The peculiarities of the valence band structure have been discussed for the crystals. The persistence of core level binding energy differences O1s–P2p and O1s–Ti2p3/2 has been detected in TlTiOPO4 and KTiOPO4, which relates well with the constancy of averaged P–O and Ti–O chemical bond lengths in this crystal family. The superstructure ordering of the TlTiOPO4 surface subjected to polishing and annealing has been detected by reflectance high energy electron diffraction (RHEED). From comparison of surface crystallographic properties of TlTiOPO4 and KTiOPO4, the most typical superstructure indices have been revealed.

First and second harmonic generation of the optical susceptibilities for the non-centro-symmetric orthorhombic AgCd2GaS4

We present the results of an ab initio theoretical study of the linear and nonlinear optical susceptibilities for the AgCd2GaS4 using the full potential linearized augmented plane wave (FP-LAPW) method as implemented in the WIEN2K code. We have used the Engel–Vosko exchange–correlation potential which is based on the generalized gradient approximation. Our calculations show that the valence band maximum (VBM) and conduction band minimum (CBM) are located at Γ resulting in a direct energy gap. We present calculations of the frequency-dependent complex dielectric function e(ω). Our calculations show that the edge of the optical absorption for e2xx(ω) and e2zz(ω) are located around 2 eV. The linear optical properties show a strong negative uniaxial anisotropy. The optical properties are scissors corrected to match the calculated energy gap with the measured one. The optical properties are analyzed in terms of the calculated electronic structure. The imaginary and real parts of the second-order SHG susceptibility were evaluated. Our calculation shows that χ333(2)(ω) is the dominant component which shows the largest total Reχijk(2)(0) value 2.0 pm V−1.

Electronic structure of AgCd2GaS4

The electronic structure of AgCd2GaS4 crystal has been studied with X-ray photoelectron spectroscopy (XPS). Chemical bonding effects have been observed by comparative analysis of binding energies of element core levels and crystal structure of AgCd2GaS4 and several ternary sulfides. It has been shown for Ga-bearing sulfides that the increase of mean chemical bond length between gallium and sulfur ions is directly related to the decrease of chemical shift of cation core level binding energy.

Restoration of KTiOPO4 surface by annealing

Abstract Superstructure ordering with a=a0, b=b0 and c=4c0 has been observed for KTiOPO4 surfaces annealed at the temperatures 200–800 °C by reflection high energy electron diffraction. The surface decomposition with the precipitation of TiO2 as anatase polycrystal modification has been revealed in the temperature range 800–900 °C.

Sellmeier equations for green, yellow, and orange colored HgGa2S4 crystals

Modeling and experimental study on phase matching of second harmonic generation in different color HgGa2S4 crystals are carried out. Using the known Sellmeier equations, the dispersion relation with weighting proportionally to short-wavelength boundary of the crystal transparency band is proposed. Optimal dispersion relations and phase-matched conditions for different color HgGa2S4 crystals can be specified.

Amorphization and chemical modification of β-BaB2O4 surface by polishing

Abstract Structure and chemical composition of mechanically polished β-BaB2O4 surface have been studied by reflection high energy electron diffraction and X-ray photoelectron spectroscopy. It has been shown that the optical surface is covered by thick layer of amorphous phase closely related to BaB2O4 in Ba/O atomic ratio and electronic structure. The presence of BaCO3 has been detected in top surface regions.

Cesium accumulation at CsB3O5 optical surface

Abstract Structure and element composition of polished CsB 3 O 5 surface have been studied. It has been shown that crystal surface is covered by thick layer (>50 A) of amorphous phase. This surface compound contains Cs, B and O and contaminated by hydrocarbons adsorbed on the surface. Element depth profiling produced by ion sputtering reveals quick and monotonic drop of C signal accompanied by increases of B and O signals with stabilization at depths higher than ∼20 A. The distribution of Cs over depth is irregular, top surface cesium content is ∼30% higher then that achieved for higher sputtering times. Being removed by sputtering, this top surface layer enriched by Cs is restored by few hours keeping at 24 °C in vacuum or air.

Synthesis, Crystal Structure, and Optical Gap of Two-DimensionalHalide Solid Solutions CsPb 2 (Cl 1– x Br x ) 5

Exploring new perovskite-related solid-state materials and the investigating composition-dependent structural and physical properties are highly important for advanced functional material development. Herein, we present the successful hydrothermal synthesis of tetragonal CsPb2Cl5 and the anion-exchange phase formation of CsPb2(Cl1- xBr x)5 ( x = 0-1) solid solutions. The CsPb2(Cl1- xBr x)5 crystal structures, which crystallize in the tetragonal system, space group I4/ mcm, with parameters similar to those of CsPb2Cl5, have been determined by Rietveld analysis. The optical band gap was obtained by UV-vis spectroscopy, and the band structure was further calculated by the full-potential method within the generalized gradient approximation. It was revealed that the band gap in CsPb2(Cl1- xBr x)5 solid solutions can be tuned over the range of 4.5-3.8 eV by anion substitution.

Acentric phase formation in AgLnX 2 (Ln = Dy, Ho, Er; X = S, Se, Te) compounds

Available information on polymorph modifications observed for AgLnX2 (Ln = Dy, Ho, Er; X = S, Se, Te) compounds has been analyzed comparatively. Cubic poly-morph with mixed (0.5Ag + 0.5Ln) cation positions is generally formed at high temperatures. Formation of monoclinic, orthorhombic and tetragonal acentric crystals is found at low temperature depending on the anion type.