Effect of temperature and isomorphic atom substitution on optical absorption edge of TlInS2xSe2(1‐x) mixed crystals (0.25 ≤ x ≤ 1)

The optical properties of the TlInS_2xSe_2(1‐x)mixed crystals (0.25 ≤ x ≤ 1) have been investigated through the transmission and reflection measurements in the wavelength range of 400–1100 nm. The optical indirect band gap energies were determined by means of the analysis of the absorption data. It was found that the energy band gaps decrease with the increase of selenium atoms content in the TlInS_2xSe_2(1‐x)mixed crystals. The transmission measurements carried out in the temperature range of 10–300 K revealed that the rates of change of the indirect band gaps with temperature are γ = –9.2×10^–4 eV/K, –6.1×10^–4 eV/K, –4.7×10^–4 eV/K and –5.6×10^–4 eV/K for TlInS₂, TlInS_1.5Se_0.5, TlInSSe and TlInS_0.5Se_1.5 crystals, respectively. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The internal friction and elastic modulus of amorphous Pd–Si and Fe–P–C alloys

The internal friction and the shear modulus of the amorphous Pd₈₀–Si₂₀–, Fe₈₀–P₁₃–C₇ and Fe₅₀–Ni₃₃–P₁₂–C₅ alloys have been measured at about 0.5 Hz over a temperature range from room temperature to about 550°C. The internal friction rises steeply with temperature and shows maxima around the crystallization temperature. The activation energy for the steeply rising internal friction has been estimated by the two different procedures; from the shift of the curve by the frequency change and from the slope of the In Q^?1 versus 1/T plot. The two values are very different, which indicates the existence of a wide distribution of activation energies. Crystallization of the amorphous alloys resulted in an increase of about 30% in the shear modulus.     

Crystallization of amorphous Ni55Pd35P10 alloys

The crystallization of Ni₅₅Pd₃₅P₁₀ alloys was examined by isochronal resistivity and hardness measurements, along with observations of the phase transformation in the heating stage of a transmission electron microscope (TEM). The resistivity temperature coefficient between 26 and 250°C is low (9.38 × 10^?5/°C); a few metastable phases form on crystallization. The hardness-temperature curve shows the hardness to increase as the metastable phases appear.     

Temperature dependence of dielectric losses in chalcogenide glasses

The frequency (2 × 10⁴?2 × 10⁷ Hz) and temperature (250–600 K) dependence of the imaginary part of the permittivity, ?′', of As₂Se₃ and Tl₂SnSe_8.61 is explained within a theoretical model. The dielectric premittivities of these compounds are correctly explained by means of a model of a hopping process over a potential barrier between localized sites.We have found that the glassy system of chalcogenide can exist in the form of dipoles. The theory shows, in agreement with the experimental results, that ?′' = Aω^m, where m is a function of temperature.     

Ionic conductivity of KMgCr(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript> molybdate

The ionic conductivity σ of KMgCr(MoO₄)₃ crystal has been investigated in a temperature range of 575–932 K by impedance spectroscopy in the frequency range of (5–5) × 10⁵ Hz. Ternary molybdate was obtained from the initial MgMoO₄ and KCr(MoO₄)₂ reagents by solid-phase technique in air at 923–973 K for 200 h. The temperature dependence σ(T) of a ceramic sample exhibits a jump of σ by a factor of about 4 at 833 ± 5 K, which is caused by the first-order phase transition. The σ value above the phase-transition temperature reaches 6 × 10^–4 S/cm (932 K) at an ion-transport activation enthalpy of 0.84 ± 0.05 eV. The most likely carriers in KMgCr(MoO₄)₃ are K⁺ cations.     

Growth and spectral properties of Er:Gd2SiO5 crystal

Er³⁺-doped Gd₂SiO₅ (Er:GSO) single crystal with dimensions of ? 35×40 mm³ has been grown by the Czochralski method. The absorption and fluorescence spectra of the Er:GSO crystal were measured at room temperature. The spectral parameters were calculated based on Judd–Ofelt theory, and the intensity parameters Ω₂, Ω₄ and Ω₆ are obtained to be 6.168×10^?20, 1.878×10^?20, and 1.255×10^?20 cm², respectively. The emission cross-section has been calculated by Fuechtbauer–Ladenbury formula.     

Investigation of zirconium phosphate Zr<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>4</Subscript> during heating

Zirconium phosphate Zr₃(PO₄)₄ has been synthesized by the sol-gel technique and investigated using X-ray powder diffraction, IR spectroscopy, and differential scanning calorimetry. It has been established that the symmetry of the unit cell, R \(\bar 3\) c, which is characteristic of the NaZr₂(PO₄)₃ (NZP) family, is lowered to P \(\bar 3\) c. The behavior of the zirconium phosphate during heating has been examined using high-temperature X-ray diffraction at temperatures ranging from 25 to 575°C. It has been revealed that the structure of the zirconium phosphate is hardly subjected to expansion due to heating in the temperature ranges 25–125°C (α _a < 1 × 10^?6 K^?1, α _c < 1 × 10^?6 K^?1, Δα < 1 × 10^?6 K^?1) and 325–575°C (α _a = ?1.4 × 10^?6 K^?1, α _c < 1 × 10^?6 K^?1, Δα < ?2.4 × 10^?6 K^?1). In the temperature range 125–325°C, the synthesized compound undergoes a second-order phase transition (upon heating), which is accompanied by the contraction of the structure along all crystallographic directions. Upon cooling in the range from 75 to 25°C, the phase transition is accompanied by the expansion of the structure.     

Temperature dependence of the dielectric parameters of nonstoichiometric SrTiO3 single crystals

The results of experimental studies of the temperature dependence of the low-frequency permittivity ε ₀ and the loss tangent taδ of nominally undoped and doped single crystals of strontium titanate at T = 10–300 K are given. The samples were doped with ions of iron-group metals (V, Mn, Fe, Co) and/or ions of rare earth metals (Pr, Nd, Sm, Tm) with concentrations of 10^?3?5 × 10^?1 at %. Anomalous temperature dependences ε₀ T and tanδ(T) were found for a number of samples. The anomalies found were attributed to the violation of stoichiometry of the single crystals under study and the transition of some fraction of Ti⁴⁺ ions to the Ti³⁺ state.     

Ionic Conductivity of KTiOPO<Subscript>4</Subscript> Single Crystals Grown by Flux Crystallization under Different Conditions

The ionic conductivity of three KTiOPO₄ crystals grown from high-temperature solution–melts in combination with the Czochralski technique under different conditions has been investigated. The first crystal was obtained at a cooling rate V_g = 0.2–0.5 mm/day and a ratio of potassium and phosphorus concentrations in the solution–melt [K]/[P] = 2. The other two crystals were grown at a much higher velocity (V_g = 3–7 mm/day) from solution–melts with [K]/[P] = 1.5 and 1. It is shown that the crystal grown upon slow cooling at [K]/[P] = 2 has the lowest ionic conductivity: σ_||c = 1.0 × 10^–5 and 3 × 10^–11 S/cm at 573 and 293 K, respectively.     

Computer simulation of ion transport in a new cathode material PrSrCuO4-δ

Oxygen diffusion in the new class of cuprates Pr_2-x Sr _x CuO_4-δ (x = 1) with perovskite structure has been simulated in the temperature range of 300–2100 K for the first time. A calculation has shown the presence of anisotropy of oxygen motion: the oxygen transport in PrSrCuO_3.7 in the temperature range of 300–2100 K is mainly two-dimensional, with an activation energy of no more than 0.40 eV. The coefficient of thermal expansion of PrSrCuO_3.7 (9.9 × 10^?6 K^?1 in the range 1300–2100 K) and the oxygen diffusivity in it, which exceed the corresponding values for La_2-x Sr _x CuO_4-δ, indicate that this compound is promising as an electrode material with a mixed ionic-electronic conductivity for various electrochemical devices. The results expand the previous concepts of the oxygen-ion transport in complex cuprates.     

A local structure change of bulk Pd40Ni40P20 glass during full relaxation

The change in the amorphous structure of bulk Pd₄₀Ni₄₀P₂₀ glass during structural relaxation was examined by an anomalous X-ray scattering (AXS) experiment with energies near the Ni K-absorption edge. It was confirmed by differential scanning calorimetry that the sample reached a meta-stable state (a fully relaxed state) with an equilibrium free volume concentration after annealing for about 1 × 10⁴ s at 563 K and 4 × 10⁴ s at 557 K just below the glass transition temperature T_g = 567 K. The structural changes on the progression toward a fully relaxed state were examined in samples annealed for 1 × 10³ and 2 × 10⁴ s at 563 K (glass A), and for 3.2 × 10³, 1 × 10⁴ and 7 × 10⁴ s at 557 K (glass B). The structural analysis revealed that the coordination number of Ni–Ni like atom pairs increased with annealing time and that of Ni–Pd, unlike atom pairs, decreased. Meanwhile, the coordination number N_PNi of P–Ni atom pairs and the nearest neighbor distance r_PNi did not show a remarkable variation. However, prolonged annealing of 7 × 10⁴ s at 557 K induced a remarkable change in N_PNi and r_PNi.     

Optical band gap and Raman spectra in some (Bi2O3)x(WO3)y(TeO2)100−x−y and (PbO)x(WO3)y(TeO2)100−x−y glasses

The glasses representing (Bi₂O₃)_x(WO₃)_y(TeO₂)_100?x?y and (PbO)_x(WO₃)_y(TeO₂)_100?x?y systems were prepared. The dilatometric glass-transition temperatures of examined glass samples were found in the region 383–434 °C, the coefficient of thermal expansion varied from 12 to 16 ppm/°C and the density ranged from 6.30₂ to 6.80₈ g/cm³. From the optical transmission measurements of thin glassy bulk samples prepared by a glass blowing, the optical gap values were found in the narrow region 3.21–3.36 eV. For the temperature interval 300–480 K, the values of the temperature coefficient of the optical band gap varied from 3.7 × 10^?4 to 5.24 × 10^?4 eV/K. It is suggested that Raman feature observed at around 350 cm^?1 can be assigned to an overlap of Raman bands attributed to WO₆ corner shared octahedra and to the following three atomic linkages: Bi–O–Te, Pb–O–Te and W–O–Te.     

Hydrogen permeation in the metallic glass Fe40Ni40P14B6

Hydrogen permeation from the gas phase through the metallic glass Fe₄₀Ni₄₀P₁₄B₆ (Metglas 2826) was measured with the electrochemical technique over 313 to 353K and 10⁵ to 10³ Pa. Specimen surfaces were coated with a thin layer of electrodeposited palladium to eleminate surface impedances to hydrogen entry and exit. Sievert's law behavior was observed over the temperature and pressure ranges studied. An excellent fit to the permeation transients as obtained from Fick's diffusion theory. Diffusivities derived from least squares fitting of permeation trasients were in good agreement with those obtained from time lag measurements. Within the concentration range studied, diffusivity was found to be independent of input hydrogen concentration. The expressions for the permeability coefficient, 2.24 × 10¹⁶ exp{[(48.99 ± 2.93) kJ/mol]/RT} atom H/ms $\text{Pa}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$, the diffusivity 8.52 × 10^?7 exp{[(?47.07 ± 1.63) kJ/mol]/RT} m²/s, and the solubility, 2.62 × 10²²exp{[(?1.92 ± 4.56) kJ/mol]/RT} atom H/m³$\text{Pa}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$, were determined.An annealing treatment at 573K for one hour decreases bot the permeability and diffusivity of hydrogen in the metallic glass.     

Electrical conductivity and thermoelectric power of liquid AgSb Te2

The electrical conductivity and thermoelectric power of liquid AgSb Te₂ have been investigated as a function of temperature. Experimental data are analyzed in terms of a recent model proposed by Mott. The activation energy for electrical conductivity and thermoelectric power is found to be approximately 0.50 eV with a large temperature coefficient γ ～ 7 × 10^?4 eV/deg K. The gradual transition from a semiconducting to a metallic behaviour has been observed at high temperature.     

Structural Conditionality of the Ionic Conductivity of MTiORO<Subscript>4</Subscript> (M = K,Rb; R = P,As) Single Crystals

The ionic conductivity σ_||c along the crystallographic axis c and the structural imperfection of the lattices of KTiOPO₄, RbTiOPO₄, and RbTiOAsO₄ single crystals with low defect concentration, grown by the high temperature solution growth technique, have been investigated by impedance spectroscopy and X-ray diffraction analysis. Isomorphic substitutions of Rb⁺ ions for conduction K⁺ cations in MTiOPO₄ crystals decreases the σ_||c value, whereas the substitution of As⁵⁺ ions for framework P⁵⁺ cations in RbTiORO₄ crystals increases the σ_||c value. The σ_||c values at 573 K are found to be 1.0 × 10^–5, 5.7 × 10^–6, 2.0 × 10^–6, and 3.3 × 10^–5 S/cm for the KTiOPO₄, RbTiOPO₄ {100}, RbTiOPO₄ {201}, and RbTiOAsO₄ crystals, respectively (the growth zone of the crystalline boule from which the samples were cut is indicated in braces).     

Electrical conductivity of Cs<Subscript>2</Subscript>CuCl<Subscript>4</Subscript> crystals

The electrical conductivity of Cs₂CuCl₄ single crystals, synthesized by crystallization from aqueous solutions in the CsCl–CuCl₂–H₂O system, has been investigated. The temperature dependence of the electrical conductivity of crystals in a temperature range of 338–584 K exhibits no anomalies. The electrical transfer activation enthalpy is ΔH_σ = 0.72 ± 0.05 eV and the conductivity is σ = 3 × 10^–4 S/cm at 584 K. The most likely carriers in Cs₂CuCl₄ are Cs⁺ cations, which transfer electric charge according to the vacancy mechanism.     

Influence of structural ordering on ion transport in BiO<Subscript>0.5</Subscript>F<Subscript>2.0</Subscript> bismuth oxyfluoride

The influence of structural defect ordering on ionic conductivity (σ) in the cubic (fluorite) modification of BiO_0.5F_2.0 oxyfluoride has been investigated. Upon cooling, the disordered fluorite BiO_0.5F_2.0 phase undergoes a reversible transition to an ordered form. This transition manifests itself as a jump in the temperature dependence σ(T) near 583 ± 6 K. The ordering of structural defects deteriorates the characteristics of ion transport in BiO_0.5F_2.0. At 500 K, the σ value for the ordered phase is 1 × 10⁻⁴ S/cm, whereas an extrapolation to this temperature for the disordered phase gives σ = 4 × 10⁻⁴ S/cm.     

Hopping conduction in amorphous Nb2O5 thin films

The low field conduction mechanism in amorphous Nb₂O₅ doped with Nb is investigated by measurements of the ac conductivity as a function of frequency (3 Hz?6 × 10⁶ Hz), dc conductivity as a function of temperature (100–400 K), capacitance as a function of frequency (3 Hz?6 × 10⁶ Hz) and conductance G as a function of voltage at 10³ Hz. Loss tangent and quality factor data are also given because of their technical and scientific relevance. Evidence for hopping conduction at low applied fields is presented by the following results: (1) a monotonic increase in ac conductivity σ(ω)αωⁿ where 0.5 < n < 1.0 in the range 3 Hz?6 × 10⁶ Hz; (2) a linear dependence of current on voltage at low fields; and (3) low activation energy for dc conduction with a transition at 210 K to a still lower activation energy; and (4) a decrease in polarizability with frequency. At high fields, E > 10⁵ V/cm, dc conductivity is dominated by the field emission mechanism of the Poole-Frenkel or Poole type.     

Solid–liquid interfacial energy of neopentylglycol solid solution in equilibrium with neopentylglycol–(D) camphor eutectic liquid

The grain boundary groove shapes for equilibrated solid neopentylglycol (NPG) solution (NPG–3 mol% D-camphor) in equilibrium with the NPG–DC eutectic liquid (NPG–36.1 mol% D-camphor) have been directly observed using a horizontal linear temperature gradient apparatus. From the observed grain boundary groove shapes, the Gibbs–Thomson coefficient (Г), solid–liquid interfacial energy (σ_SL) of NPG solid solution have been determined to be (7.5±0.7)×10^?8 K m and (8.1±1.2)×10^?3 J m^?2, respectively. The Gibbs–Thomson coefficient versus T_mΩ^1/3, where Ω is the volume per atom was also plotted by linear regression for some organic transparent materials and the average value of coefficient (τ) for nonmetallic materials was obtained to be 0.32 from graph of the Gibbs–Thomson coefficient versus T_mΩ^1/3. The grain boundary energy of solid NPG solution phase has been determined to be (14.6±2.3)×10^?3 J m^?2 from the observed grain boundary groove shapes. The ratio of thermal conductivity of equilibrated eutectic liquid to thermal conductivity of solid NPG solution was also measured to be 0.80.     

Growth of large KDP single crystals for UV spectrum range

The influence of various technological parameters of crystallization (acidity of growth solutions, crystallization temperature, growth rate, degree of solution purification) on the optical absorption of large KDP single crystals has been studied in the UV range of the spectrum. It is shown that the method of solvent recirculation with the use of the starting material with the microimpurity content not exceeding 5 × 10^?5 wt % and solution ultrafiltration under the optimum crystallization conditions (t_cr = 80°C, V_cr ～ (0.8–1.6) × 10^?6 cm/s, pH 4) enables one to grow KDP single crystals with cross sections up to 300 × 300 mm² and the transmission in the vicinity of the fundamental absorption edge λ = 200 nm) equal to 86%.