Optically addressed As<Subscript>50</Subscript>Se<Subscript>50</Subscript>-liquid crystal structure highly sensitive to He-Ne laser radiation

An optically addressed structure of the As _x Se_1-x -liquid crystal (LC) type, with the photoconductor composition deviating from stoichiometry toward excess arsenic, has been tested using holographic techniques. It is established that the As₅₀Se₅₀-LC structure (with maximum possible arsenic content in the photoconductor) exhibits record high sensitivity (2.2 × 10^?7 W/cm²) at a He-Ne laser radiation wavelength. Based on this structure, it is possible to implement nonlinear optical data-processing algorithms employing the entire transmission characteristic including the inversion region. The maximum diffraction efficiency achieved with the As₅₀Se₅₀-LC structure amounts to 36.5%.     

Effect of Oxygen Impurity on the Optical Transmission of As2Se3.4Glass

As₂Se_3.4glass samples with controlled oxygen content in the range (1.4–7.9) × 10^–2wt % were used to assess the effect of oxygen impurity on the IR absorption spectrum of the glass. The spectral dependence of the extinction coefficient for oxygen impurity was determined in the range 600–1400 cm^–1. It was shown that the presence of 10^–5wt % O gives rise to additional losses comparable to the intrinsic losses in the CO₂lasing range.     

Phase transitions and high-temperature crystal chemistry of polymorphous modifications of Cs<Subscript>2</Subscript>(UO<Subscript>2</Subscript>)<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)

Phase transitions and thermal deformations of - and -Cs₂(UO₂)₂(MoO₄)₃ were studied by high-temperature X-ray diffraction analysis. In heating of -Cs₂(UO₂)₂(MoO₄)₃ to 625 ± 25°C, the reconstructive phase transition proceeds. -Cs₂(UO₂)₂(MoO₄)₃ is stable up to 700 ±25°C. The thermal expansion of both phases is sharply anisotropic: ₁₁ = 10 × 10^–6, ₂₂ = 33 × 10^–6, ₃₃ = 10 × 10^–6, _V = 53 × 10^–6 deg^–1 for -Cs(UO₂)₂(MoO₄)₃ and ₁₁ = 13 × 10^–6, ₃₃ = 3 × 10^–6, _V = 31 × 10^–6 deg^–1 for -Cs₂ (UO₂)₂ (MoO₄)₃. The anisotropy of thermal expansion is explained by features of the crystal structure of the compounds.Translated from Radiokhimiya, Vol. 46, No. 5, 2004, pp. 405–407.Original Russian Text Copyright © 2004 by Nazarchuk, Krivovichev, Filatov.     

Photocurrent and Optical Transmission Spectra of Sn- and Pb-Doped (As<Subscript>2</Subscript>S<Subscript>3</Subscript>)<Subscript>0.3</Subscript>(As<Subscript>2</Subscript>Se<Subscript>3</Subscript>)<Subscript>0.7</Subscript> Glass Films

The photocurrent and optical transmission spectra of thin (As₂S₃)_0.3(As₂Se₃)_0.7 glass films doped with Sn and Pb are reported. The strongest photoresponse is offered by the films doped with 0.010– 0.015 at % Sn or Pb. Low doping levels are shown to have a significant effect on the peak-response wavelength and band gap of the films.     

Optical and photoelectric properties of Cd<Subscript>1 - <Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript>x</Subscript>As<Subscript>2</Subscript> single crystals

The optical absorption, photoconductivity, and short-circuit photocurrent spectra of structurally perfect Cd_{1 - x} Zn_xAs₂ (x = 0.03, 0.05, 0.06) single crystals are studied for the first time near the intrinsic edge in the range 80–300 K. The results demonstrate that the intrinsic edge in the solid solutions is due to indirect transitions involving the formation of excitons for both the E c and E c polarizations. The indirect gaps _g ⁱ of the solid solutions are determined. In the range 80–300 K, the data for x = 0–0.06 and both polarizations are well fitted by _g ⁱ (x) = _g ⁱ (0) + 0.0866x + 2.35x ². The introduction of 6 mol % ZnAs₂ into CdAs₂ increases its _g ⁱ by 14 meV.Translated from Neorganicheskie Materialy, Vol. 41, No. 3, 2005, pp. 268–272.Original Russian Text Copyright © 2005 by Morozova, Marenkin, Mikhailov, Koshelev.This revised version was published online in April 2005 with a corrected cover date.This revised version was published online in April 2005 with a corrected cover date.     

Spectral parameters of Nd<Superscript>3+</Superscript> ion in Sr<Subscript>6</Subscript>NdSc(BO<Subscript>3</Subscript>)<Subscript>6</Subscript> crystal

The spectroscopic study of Nd³⁺ in Sr₆NdSc(BO₃)₆ crystal had been performed. Based on the Judd-Ofelt theory to analyze the optical strengths measured in absorption spectra, the following spectral parameters were obtained: intensity parameters are ₂ = 1.108 × 10^–20 cm², ₄ = 2.884 × 10^–20 cm², ₆ = 3.085 × 10^–20 cm², the radiative lifetime is 385 s, the quantum efficiency is 12.5%. The fluorescence branch ratios were calculated: ₁ = 0.423, ₂ = 0.482, ₃ = 0.092, ₄ = 0.005.     

Spectral parameters of Er<Superscript>3+</Superscript> ion in Yb<Superscript>3+</Superscript>/Er<Superscript>3+</Superscript>:KY(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> crystal

The spectral parameters of Er³⁺ in Yb³⁺/Er³⁺:KY(WO₄)₂ crystal with space group C2/c have been investigated based on Judd-Ofelt theory. The spectral parameters were obtained: the intensity parameters are: ₂ = 6.33 × 10^–20 cm², ₄ = 1.35 × 10^–20 cm², ₆ = 1.90 × 10^–20 cm². The radiative lifetime and the fluorescence branch ratios were calculated. The emission cross section _e (at 1536 nm) is 2.0 × 10^–21 cm².     

Kinetics of Ge<Subscript>20</Subscript>Se<Subscript>80-x</Subscript>As<Subscript>x</Subscript> (<Emphasis Type="Italic">x</Emphasis> = 0, 5, 10, 15 and 20) in glass transition region

The results of differential scanning calorimetric (DSC) measurements on Ge₂₀Se_{80- x}As_x (x = 0, 5, 10, 15 and 20) system with the specific aim of investigating the effect of heating rate and composition on glass transition temperature have been discussed. The results indicate that the glass transition temperature (T_g) is dependent both on the heating rate and composition. The glass transition activation energy (E_t) and heat absorbed in glass transition region (ΔH) are higher for Ge₂₀Se₆₅As₁₅ as compared to the values of other compositions of arsenic. An effort has also been made to develop an empirical model for the composition dependence of ΔH. A good agreement has been observed between the experimental values and the results of model calculation.     

X-ray diffraction study of the Cu<Subscript>2</Subscript>Se-In<Subscript>2</Subscript>Se<Subscript>3</Subscript>-Cr<Subscript>2</Subscript>Se<Subscript>3</Subscript> system near CuInCr<Subscript>2</Subscript>Se<Subscript>5</Subscript>

The structure of three compounds in the Cu₂Se-In₂Se₃-Cr₂Se₃ system near CuInCr₂Se₅ is determined by single-crystal x-ray diffraction: CuInCr₄Se₈ (I), Cu₂In₂Se₄ (II), and Cu_0.5In_0.5Se (III). I has a cubic (spinel type) structure: a = 10.606(4) Å, Z = 4, sp. gr. F43m. II has a pseudotetragonal (sphalerite type) structure: a = 5.774(2) Å, c = 11.617(6) Å. The structure of II was solved in a reduced unit cell with a = 5.774(2) Å, b = 5.774(2) Å, c = 7.095(6) Å, = 113.95(5)°, = 113.95(5)°, = 90.00(4)°, Z = 1, sp. gr. P1. III has a triclinic cell (disordered structure of II): a = 4.088(1) Å, b = 4.091(2) Å, c = 4.101(1) Å, = 60.05(1)°, = 60.08(1)°, = 89.98(4)°, Z = 1, sp. gr. P1. The Cu and In atoms in I sit in inequivalent tetrahedral sites, and the Cr atoms reside in octahedral interstices of the close packing of Se atoms. The bond lengths are In–Se = 2.538(6), Cr(1)–Se(1) = 2.514(7), Cr(1)–Se(2) = 2.576(8), and Cu–Se = 2.437(5) Å. In II, all of the atoms sit in tetrahedral sites; the mean bond lengths are In–Se = 2.578(6) and Cu–Se = 2.44(1) Å. In III, the Cu and In atoms are fully disordered in the same tetrahedral site; the mean Cu(In)–Se bond length is 2.508(6) Å.Translated from Neorganicheskie Materialy, Vol. 40, No. 12, 2004, pp. 1435–1439.Original Russian Text Copyright © 2004 by Antsyshkina, Sadikov, Koneshova, Sergienko.     

Effect of preparation conditions on the optical and photoluminescent properties of glassy As<Subscript>2</Subscript>S<Subscript>3</Subscript>

We have studied the 77-K photoluminescent properties of As₂S₃ semiconducting glass prepared at different temperatures (T ₁ = 870 K; T ₂ = 1120 K; T ₃ = 1370 K) and cooling rates (v ₁ = 10^?2 K/s, v ₂ = 1.5 K/s, v ₃ = 1.5 × 10² K/s). The results demonstrate that the structural, optical, and photoluminescent properties of semiconducting chalcogenide glasses can be tuned over a considerable range by varying the preparation conditions.     

Heat Capacity and Thermodynamic Functions of Ga<Subscript>2</Subscript>Se<Subscript>3</Subscript> from 14 to 320 K

The heat capacity of Ga₂Se₃ is measured from 14 to 320 K by adiabatic calorimetry. The smoothed heat capacity data are used to evaluate temperature-dependent thermodynamic functions (entropy, enthalpy increment, and reduced Gibbs energy) of gallium selenide. Under standard conditions, the thermodynamic properties of Ga₂Se₃ are C _p ⁰ (298.15 K) = 120.8 ± 0.2 J/(K mol), S⁰(298.15 K) = 180.4 ± 0.4 J/(K mol), H⁰(298.15 K) - H⁰(0) = 25.32 ± 0.05 kJ/mol, and Φ⁰(298.15 K) = 95.52 ± 0.19 J/(K mol). The Debye characteristic temperature of Ga₂Se₃ evaluated from heat capacity data is 340 ± 10 K.     

Thermal Conductivity of Chalcogenide As<Subscript>2</Subscript>S<Subscript>3</Subscript> Thin Films

In order to investigate the photo-induced thermal property changes in chalcogenide thin films, amorphous As ₂ S ₃ thin film samples, whose thicknesses are 0.5, 1.0, 2.0, and 4.0 m, were prepared on silicon wafers by thermal evaporation. Their thermal conductivity was measured by the 3 method between room temperature and 100 °C. These measurements were repeated after the illumination of an Ar⁺ laser beam whose photon energy is consistent with the bandgap energy of As ₂ S ₃, and repeated again for annealed films at 180 °C for 1 h. The result shows that the thermal conductivities of fresh films were 0.14 to 0.27 W·m ^–1·K ^–1; however, the values increase to 0.28–0.47 W·m ^–1·K ^–1 after illumination of the sample and decrease to 0.19–0.42 W·m ^–1·K ^–1 after annealing of the sample. These changes can be explained by the change in microstructure produced from the photo-darkening and thermal annealing.     

Effect of N<Subscript>2</Subscript> gas annealing and SiO<Subscript>2</Subscript> barrier on the optical transmittance and electrical resistivity of a transparent Sb-doped SnO<Subscript>2</Subscript> conducting film

During the fabrication process of transparent conducting thin films of ATO (antimony-doped tin oxide) on a soda lime glass substrate by a sol-gel dip coating method, the effects of the SiO₂ buffer layer formed on the substrate and N₂ annealing treatment were investigated quantitatively. The deposited ATO thin film was identified as a crystalline SnO₂ phase and the film thickness was about 100 nm/layer at a withdrawal speed of 50 mm/min. Optical transmittance and electrical resistivity of the 400 nm-thick ATO thin film that was deposited on SiO₂ buffer layer/soda lime glass and then annealed under nitrogen atmosphere were 84% and 5.0 × 10^–3cm, respectively. The XPS analysis confirmed that a SiO₂ buffer layer inhibited Na ion diffusion from the substrate, preventing the formation of a secondary phase such as Na₂SnO₃ and SnO and increasing Sb ion concentration and ratio of Sb⁵⁺/Sb³⁺ in the film. It was found that N₂ annealing treatment leads to the reduction of Sn⁴⁺ as well as Sb⁵⁺, however the reduction of Sn⁴⁺ is more effective, and consequently results in a decrease in the electrical resistivity to produce excellent electrical properties in the film. © Springer Science + Business Media, Inc.     

Ionic conductivity in the Lu<Subscript>2</Subscript>O<Subscript>3</Subscript>-TiO<Subscript>2</Subscript> system

Nanocrystalline Lu₂O₃-TiO₂ (33.3–44 mol % Lu₂O₃) materials with a partially disordered pyrochlore structure, prepared via heat treatment in the range 1400–1750°C, are found to possess high oxygen ionic conductivity. Their 740°C conductivity is 10^-3 to 10^-2 S/cm, depending on the heat-treatment temperature and composition, which is comparable to that of the well-known fluorite solid electrolyte ZrO₂-9 mol % Y₂O₃.Translated from Neorganicheskie Materialy, Vol. 41, No. 3, 2005, pp. 324–331.Original Russian Text Copyright © 2005 by Shlyakhtina, Mosunov, Stefanovich, Knotko, Karyagina, Shcherbakova.This revised version was published online in April 2005 with a corrected cover date.This revised version was published online in April 2005 with a corrected cover date.     

Electric-field and temperature effects on electric currents in polycrystalline ZnGa<Subscript>2</Subscript>Se<Subscript>4</Subscript>

The current (electrical transport) through In/ZnGa₂Se₄/In structures has been measured as a function of temperature and applied electric field at temperatures from 77 to 400 K in fields from 10 to 3 × 10⁴ V/cm. The results are analyzed in terms of the Poole-Frenkel effect and space-charge-limited currents. The activation energy of traps and trap concentration in ZnGa₂Se₄ and its refractive index are determined to be E _t= 0.8 eV, N _t = 4 × 10¹³ cm^?3, and n = 2.4, respectively.     

High-temperature phase transition of Tm<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript>

The high-temperature (>1600°C) order—disorder phase transition of Tm₂Ti₂O₇ is shown to be irreversible. The 740°C ionic conductivity of nanocrystalline Tm₂Ti₂O₇ ceramics synthesized at 1670°C is 2 × 10^-3 S/cm and remains unchanged upon heat treatment in air at 860°C for 240 h. The conductivity of the high-temperature (disordered pyrochlore) phase of Tm₂Ti₂O₇ is independent of grain size in the range 20–30 nm.Translated from Neorganicheskie Materialy, Vol. 40, No. 12, 2004, pp. 1495–1500.Original Russian Text Copyright © 2004 by Shlyakhtina, Knotko, Larina, Borichev, Shcherbakova.     

Kinetics of mechanically activated P<Subscript>2</Subscript>O<Subscript>5</Subscript> incorporation into Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

The incorporation of phosphoric anhydride into - and -aluminas during mechanical activation is investigated. An empirical equation is proposed for the kinetics of P₂O₅ incorporation. The effect of the specific power of the mill on the amount of bound P₂O₅ is analyzed.Translated from Neorganicheskie Materialy, Vol. 41, No. 3, 2005, pp. 321–323.Original Russian Text Copyright © 2005 by Kosenko, Smirnova, Denisova.This revised version was published online in April 2005 with a corrected cover date.This revised version was published online in April 2005 with a corrected cover date.     

In-field Conductivity Fluctuations in Ba<Subscript>0.72</Subscript>K<Subscript>0.28</Subscript>Fe<Subscript>2</Subscript>As<Subscript>2</Subscript> Single Crystals

Fluctuations in the conductivity of Ba_0.72K_0.28Fe₂As₂ single crystal are studied systematically by resistance measurements as a function of temperature and magnetic field. A clear Maki?Thompson and Aslamakov?Larkin (MT–AL) two- to three-dimensional (2D–3D) crossover is found on the excess conductivity (Δσ) curves as the temperature approaches the superconducting critical temperature, T _c. 3D fluctuations in superconductivity are realized near T _c that are well fitted to experimental data by the 3D Aslamazov–Larkin theory. The Maki–Thompson model shows a 2D conductivity fluctuation above the 2D-3D temperature transition, T ₀, which depends on magnetic field. Results show that the 2D-3D dimensional crossover moves to lower temperature with increasing magnetic field. The values of the transition temperature and the crossover in the reduced temperature, ln(ε ₀), as functions of magnetic field were used to determine the coherence length and the lifetime, τ _φ , of the fluctuational pairs at the temperature of 35 K. Analysis of the Ba_0.72K_0.28Fe₂As₂ single crystal gives a value of 3.76 × 10^??12 s for the τ _φ in the absence of magnetic field and it decreases to 2.4 × 10^??12 s in magnetic field of 13 T.     

Phase equilibria in the Ag<Subscript>2</Subscript>Se-As<Subscript>2</Subscript>Se<Subscript>3</Subscript>-Bi<Subscript>2</Subscript>Se<Subscript>3</Subscript> system

We have studied phase equilibria in the pseudoternary system Ag₂Se-As₂Se₃-Bi₂Se₃ and constructed the 300-, 600-, and 800-K isothermal sections, a number of partial phase diagrams, and the liquidus projection of this system. The AgAsSe₂-AgBiSe₂ and As₂Se₃-AgBiSe₂ joins are shown to be pseudobinary, and the Ag₃AsSe₃-AgBiSe₂ and AgAs₃Se₅-AgAsSe₂ joins are pseudobinary below the liquidus. Several in- and univariant peritectic, eutectic, and eutectoid equilibria and a broad region of AgBiSe₂-based solid solutions are identified. The homogeneity region of the AgBiSe₂-based phase has the largest extent along the AgAsSe₂-AgBiSe₂ join: 40 mol % (650 K) for the high-temperature form of AgBiSe₂ and 20 mol % (300 K) for its low-temperature form.     

Low-loss,high-purity (TeO<Subscript>2</Subscript>)<Subscript>0.75</Subscript>(WO<Subscript>3</Subscript>)<Subscript>0.25</Subscript> glass

By melting a mixture of high-purity oxides in a platinum crucible under flowing purified oxygen, we have prepared (TeO₂)_0.75(WO₃)_0.25 glass with a total content of 3d transition metals (Fe, Ni, Co, Cu, Mn, Cr, and V) within 0.4 ppm by weight, a concentration of scattering centers larger than 300 nm in size below 10² cm⁻³, and an absorption coefficient for OH groups (λ ∼ 3 μm) of 0.008 cm⁻¹. The absorption loss in the glass has been determined to be 115 dB/km at λ = 1.06 μm, 86 dB/km at λ = 1.56 μm, and 100 dB/km at λ = 1.97 μm. From reported specific absorptions of impurities in fluorozirconate glasses and the impurity composition of the glass studied here, the absorption loss at λ ∼ 2 μm has been estimated at ≤100 dB/km. The glass has been drawn into a glass-polymer fiber, and the optical loss spectrum of the fiber has been measured.