Determination of lattice parameters and thermal expansion of CuGe2P3 + 0.2 Ge3P4 at elevated temperatures

CuGe₂P₃ is a p‐type semiconductor with zincblende structure. Ge₃P₄ is soluble up to 35 mole% in CuGe₂P₃. Lattice parameters of CuGe₂P₃ + 0.2 Ge₃P₄ have been determined at elevated temperatures from room temperature to 873 K using the x‐ray diffraction profiles (111), (200), (220), (311), (222), (400), (331), (420), (422) and (511) obtained from high temperature diffractometer. It is found that the lattice parameter increases linearly from 0.53856 nm at RT to 0.54025 nm at 873 K. The data on lattice parameter is used and coefficient of lattice thermal expansion of CuGe₂P₃ +0.2 Ge₃P₄ was determined at different temperatures. It is found that the coefficient of thermal expansion of CuGe₂P₃ +0.2 Ge₃P₄ is 5.48 x 10^‐6 K^‐1 and is independent of temperature. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

High-temperature heat capacity,thermodynamic properties and debye temperature of CuGe2P3

The heat capacity at constant pressure of CuGe₂P₃ is measured in the temperature range from 180 to 550 K. Standard enthalpies and entropies relative to 298.15 K are calculated from the heat capacity data. The Debye temperature in the high-temperature limit is estimated to be about 710 K.     

Infrared optical properties of (CuGe2P3)1−x(6 Ge)x solid solutions

Infrared reflectivity spectra of (CuGe₂P₃)_1−x(6 Ge)_x mixed crystals with compositions in the range x = 0.07–0.33 are measured at room temperature in the wavenumber range from 180 to 4000 cm⁻¹. An analysis of the spectra reveals six vibrational modes. The composition dependence of the mode frequencies and of the free carrier concentration and mobility is given and compared with infrared optical data for CuGe₂P₃.     

Infrared lattice vibrations in CuGe2P3

Infrared reflectivity spectra of CuGe₂P₃ single crystals are measured at room temperature in the wavenumber range from 180 to 4000 cm⁻¹. From an analysis of the spectra the parameters of five vibrational modes are determined. The results are discussed in terms of the Keating model and are compared with lattice vibrational data for ZnGeP₂, CdGeP₂, and CuSi₂P₃.     

Direct measurement of isothermal compressibility of amorphous semiconductors

The isothermal compressibilities of the chalcogenide glasses Te₁₅Ge₃As₂, Te₁₅Ge₂As₃ and As₂Se₃ have been measured to 5 kbar by direct measurement of the change in sample length using a differential transformer placed inside the hydrostatic pressure vessel. Calibration data was obtained from the measurement of the compressibilities of alkali halide single crystals. For Te₁₅Ge₃As₂, the isothermal compressibility was found to be 6.00 × 10^?12 ? 0.7 × 10^?22P cm²/dyne; for Te₁₅Ge₂As₃, 5.58 × 10^?12 + 0.3 × 10^?22P cm²/dyne; for As₂Se₃, 6.30 × 10^?12 ? 0.8 × 10^?22P cm²/dyne where P is the pressure in dynes/cm². Errors are near 5%.     

Hydrothermal syntheses of silver phosphate nanostructures and their photocatalytic performance for organic pollutant degradation

Photocatalysis has been recognized as a potential strategy for energy conversion and environmental remediation. In this study, we present a facile hydrothermal method for the controlled syntheses of Ag₅P₃O₁₀, Ag₄P₂O₇/Ag₃PO₄ and Ag₃PO₄ photocatalysts by using sodium triphosphate (Na₅P₃O₁₀) as the phosphate source. The phase structure and morphology of the products were investigated by X‐ray powder diffraction (XRD) and scanning electron microscopy (SEM). The photocatalytic activities of the synthesized Ag₅P₃O₁₀, Ag₄P₂O₇/Ag₃PO₄ and Ag₃PO₄ nanostructures were evaluated by the degradation of organic pollutants under simulated sunlight irradiation. The kinetics of the photocatalytic degradation reaction is presented. It is revealed that the photocatalytic activity increases in the order of Ag₅P₃O₁₀, Ag₄P₂O₇/Ag₃PO₄ and Ag₃PO₄, and the Ag₃PO₄ nanocrystals show the best photocatalytic performance. The photocatalytic mechanism was systematically investigated, and the superoxide radicals (O₂^•−) and photoinduced holes are considered to contribute mostly to the high photocatalytic activity of Ag₃PO₄.     

Ab initio calculation of vibrational frequencies of GexPxS1−2x glass

The vibrational frequencies of GeS₄, GeP₄, Ge₂S₆, GeP₃, Ge₃P, Ge₂P₂, P₂S₂, P₃S, P₄S₃, α-P₄S₄, β-P₄S₄, α-P₄S₅, β-P₄S₅, P₄S₇, P₄S₉ and P₄S₁₀ are theoretically computed from the first principles. The Raman frequencies of Ge_xP_xS_1−2x glass are obtained for x varying from 0.05 to 0.019. The computed fundamental frequencies of clusters are compared with those experimentally found. In this way, we are able to identify the vibrating clusters in the real glass. The clusters identified in the real glass are found to be Ge₂P₂, P₄S₃, α-P₄S₄, β-P₄S₄, β-P₄S₅, P₄S₇, P₄S₉, β-P₄S₅, Ge₂S₆, Ge₃P.     

A survey of the elastic properties of some semiconducting glasses under pressure

We have measured both shear and longitudinal velocities for 10 MHz sound in amorphous As₂S₃, As₂Se₃, As₂Ge₂SeTe, As₂Ge₃Te₁₅ and Cd₆GeTe and Cd₆Ge₃As₁₁ over the pressure range 0–8 kbar and the temperature range 25–100°C. A variety of elastic constants has been computed. Those glasses with larger values of the connectedness were stiffer and showed less pressure effect.     

Ultrasonic wave velocities and attenuation in IVb-Vb-VIb chalcogenide glasses: 2–300 K

The velocities and attenuation of longitudinal and shear ultrasonic (12 MHz) waves have been measured for several chalcogenide glasses (Ge₁₀Si₁₂As₃₀Te₄₈, Ge₂₀As₃₀Se₅₀, Si₂₀As₃₂Te₄₈, Ge₁₀Si₁₂As₂₉Te₄₉, Ge₁₂S₁₄As₃₅Te₄₉). The bulk, shear and Young's moduli and the Poisson ratio are found to be insensitive to the glass composition. The temperature dependences of the longitudinal and shear-wave velocities are negative at higher temperatures and approach 0 K with a zero slope. The ultrasonic attenuation does not exhibit either the broad loss peak or the smaller low-temperature peak found in many other glasses: the elastic and anelastic behaviour is quite different from that of oxide glasses — no evidence for the existence of two-level systems has been obtained from the ultrasonic measurements.     

Cluster self-organization of TR,Ge-containing crystal-forming systems: Suprapolyhedral precursors and self-assembly of La3Ga[6]Ga 4 [4] Ge[4]O14 (langasite) and La3Ge[6]Ge 2 [5] Ge 2 [4] Ga[4]O16 gallogermanates

A combinatorial-topological analysis of the La₃Ga^[6]Ga ₄ ^[4] Ge^[4]O₁₄ and La₃Ge^[6]Ge ₂ ^[5] Ge ₂ ^[4] Ga^[4]O₁₆ gallogermanates, which have MT and MPT microporous frameworks composed of M octahedra (GeO₆, GaO₆), T tetrahedra (GeO₄, GaO₄), and P pyramids (GeO₅), is performed using the method of coordination sequences with the TOPOS 3.2 program package. It is established that the La₃Ga^[6]Ga ₄ ^[4] Ge^[4]O₁₄ gallogermanate is characterized by a crystal-forming net 6 6 6 (of the graphite type). A new type of the binodal net 6 10 1 0 + 6 10 (2: 1) is revealed in the La₃Ge^[6]Ge ₂ ^[5] Ge ₂ ^[4] Ga^[4]O₁₆ gallogermanate. The cyclic cluster precursors composed of six polyhedra with a lanthanum template atom at the center of the LaMT ₅ and LaMP ₃ T ₃ clusters are identified by the two-color decomposition of the nets in the structures of the La₃Ga^[6]Ga ₄ ^[4] Ge^[4]O₁₄ and La₃Ge^[6]Ge ₂ ^[5] Ge ₂ ^[4] Ga^[4]O₁₆ gallogermanates. The coordination numbers of the cluster precursors in these structures are found to be equal to 6 and 4 for two-dimensional nets and 8 and 6 for three-dimensional nets, respectively.     

Structural and Electrical Characterization of Ag3Ga5Te9 and Ag3In5Se9 Crystals

X-ray powder diffraction studies revealed that Ag₃Ga₅Te₉ and Ag₃In₅Se₉ crystallize in orthorhombic and tetragonal systems, respectively. The temperature dependent conductivity and Hall effect measurements have been carried out between 65—480 K. Ag₃Ga₅Te₉ exhibits p-type conduction with a room temperature conductivity of 4.3 × 10^—4 (Ω · cm)^—1 and mobility less than 1 cm²/V · s. Ag₃In₅Se₉ was identified to be n-type with room temperature conductivity 7.2 × 10^—5 (Ω · cm)^—1 and mobility 20 cm²/V · s. From temperature dependence of the conductivity three different impurity ionization energies were obtained for both compounds. The anomalous behavior observed in the temperature dependence of mobility was attributed to the different features of the microstructure.     

Electrical properties of phosphate glasses

The electrical properties of glasses in the Na₂OP₂O₅, Ag₂OP₂O₅ and (1?x)Na₂OxAg₂OP₂O₅ systems have been measured over a range of temperature and composition.The properties of the Na₂OP₂O₅ and Ag₂OP₂O₅ glasses have been compared within the phosphate system as well as with silicate glasses. The silver-containing glasses show higher conductivity and lower temperature coefficients when compared with the sodium-containing glasses. A maximum in the room temperature resistivity of the (1?x)Na₂O?xAg₂O?P₂O₅ system was found around the mole ratio of 0.16:0.84 Ag₂O:Na₂O, indicating a mixed-alkali effect. A similar effect was seen in the tan δ, but not in the T_g-against-composition plots. A linear relationship was noted for the tan δ-versus-log₁₀ (resistivity) plot, as has been seen in other glass-forming systems.     

Growth,electrical and optical behaviour of nanocrystalline Ag2Cu2O3 films produced by RF magnetron sputtering

Thin films of Ag₂Cu₂O₃ were formed on glass substrates by RF magnetron sputtering technique under different oxygen partial pressures in the range 5 × 10^‐3 – 8 × 10^‐2 Pa using mosaic target of Ag₇₀Cu₃₀. The influence of oxygen partial pressure on the core level binding energies, crystallographic structure, and electrical and optical properties of the deposited films was studied. The atomic ratio of copper to silver in the films was 0.302. The oxygen content was in correlation with the oxygen partial pressure maintained during the growth of the films. The films formed at oxygen partial pressures < 2 × 10^‐2 Pa was mixed phase of Ag₂Cu₂O₃ and Ag. The films deposited at 2 × 10^‐2 Pa were single phase of Ag₂Cu₂O₃. The crystallite size of the films formed at 2 × 10^‐2 Pa was 12 nm, while those films annealed at 473 K was 16 nm. The nanocrystalline Ag₂Cu₂O₃ films formed at oxygen partial pressure of 2 × 10^‐2 Pa showed electrical resistivity of 8.2 Ωcm and optical band gap of 1.95 eV. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation of silver centres in glassy B2O3

B₂O₃ samples with silver impurities, X-ray irradiated at 77 K and then heated to 300 K, exhibit the presence of Ag⁺₂ molecular ions. It has been found that formation of Ag⁺₂ centres occurs with the participation of neutral silver atoms according to the reaction Ag⁰ + Ag⁺ → Ag⁺₂. The EPR spectra of Ag⁺₂ have been investigated and the parameters of the spin Hamiltonian have been determined. Under the action of light, λ = 390 nm, the Ag⁺₂ centres were observed to undergo photochemical decomposition into Ag⁰ atoms and Ag⁺ ions.The EPR spectra of Ag⁰ atoms have also been studied in great detail. The effect of light irradiation and temperature variation on the properties of these atoms has been investigated.     

Crystallization of MIGe2(PO4)3 (MI – Na,K, Ag) from molten phosphate media

A number of NASICON‐related M^IGe₂(PO₄)₃ (M^I – Na, K, Ag) have been prepared using a high‐temperature solution method in the molten system M^I‐Ge‐P‐O (M^I – Na, K) based on the solubility data for GeO₂ at 1123 K for the Na‐P‐O system and 1173 K for the K‐P‐O one. The single crystals of AgGe₂(PO₄)₃ were obtained after crystallization of a melt with Ag/P = 1.4. It crystallizes in the trigonal system, space group R‐3, cell parameters a = 8.06340(1) Å, c = 21.8385(4) Å, Z = 6. The framework is built up from two GeO₆ units that are isolated from each other by PO₄ tetrahedra to form the main building block of the structure [Ge₂(PO₄)₃]⁻. Two types of silver cations M1 and M2 are found to have different coordination requirements shown by the bond valence sum calculations.     

Growth of Nd:Sr3Ga2Ge4O14 crystals by a modified Bridgman method

Bridgman growth of Nd:SGG (Sr₃Ga₂Ge₄O₁₄) crystals has been investigated for the first time. Pt crucible of ∅︁25mm×250mm with a seed well of ∅︁10mm×80 mm is used, and seed is SGG crystal of ∅︁10mm×50mm grown by Bridgman method in advance. The growth parameters are optimized as the furnace temperature is set to 1450∼1500°C, temperature gradient in the crystal‐melt interface is less than 25 K/cm and growth rate is less than 0.5mm/h. The Nd:SGG crystals with 25mm in diameter and 60mm in length are grown successfully from 1.5 to 8at% Nd³⁺ doped stoichiometric Sr₃Ga₂Ge₄O₁₄ melt. The distribution coefficient and concentration of Nd³⁺ in Nd:SGG crystals are obviously higher than those of Nd:YAG crystal. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electrical properties of glassy AsxGe10Te90−x alloys

This paper analyses the electrical properties of glassy alloys of As_xGe₁₀Te_90?x, while reporting the conductivity and dielectric constant of As₅Ge₁₀Te₈₅ and As₁₅Ge₁₀Te₇₅ compositions in the temperature range 77–383 K and the frequency range from dc to 5 MHz. The dc conductivity has been shown to be of the form

The ratio σ₀₁/σ₀₂ is of the order of 10⁶. ΔE₁, the higher temperature activation energy, is dependent on the composition, while ΔE₂, the lower temperature activation energy, is less dependent on the composition. The dielectric constant has been found to be independent of temperature and frequency up to about 253 K. However, at higher temperatures, it becomes activated and proportional to log ω.Some common features of As_xGe₁₀Te_90?x are a kink in dc conductivity, a ω^0.8 relationship for ac conductivity, no evidence of variable-range hopping at low temperatures, field-dependent conductivity and memory switching. The data can be interpreted in terms of the dangling-bond theory of Mott and his collaborators. A high density of states of the order of 10²⁰eV^?1 cm^?3 near the Fermi level may be expected.     

Equilibrium vapour pressures over NaCl-AgCl melts

The variation of vapour pressures over NaCl AgCl melts with increasing of AgCl mole fractions in the interval (0.00–0.33) has been studied at 1073 K by gas transport experiments. The vapour pressures of the individual species of silver chloride [(AgCl), (Ag₃Cl₃)] and of sodium chloride [(NaCl), (Na₂Cl₂)] have been calculated using thermodynamic data. The experimental and calculated results have been used for evaluation of the vapour pressures of the complex species Ag₂NaCl₃ and AgNa₂Cl₃ at the upper experimental conditions. The equilibrium constants of the following gas-phase reactions have been computed: 2 AgCl + NaCl ⇌ Ag₂NaCl₃, K_p1073K = 2.57 · 10⁶, AgCl + 2 NaCl ⇌ AgNa₂Cl₃, K_p1073K = 1.19 · 10⁷.     

Neutron thermodiffractometry study of silver chalcogenide glasses

Silver-containing chalcogenide glasses are of considerable interest for applications in optical and electrical recordings and as solid electrolytes. Therefore, insight in their structural properties is important. A neutron thermodiffraction study of Ag_x(Ge_0.25Se_0.75)_100−x glasses with x = 15 and 25 at.% was carried out. The amorphous samples were heated in situ from room temperature up to 350 °C, while the neutron diffraction spectra were collected every degree. For both glasses the Ag₈GeSe₆ phase appeared first, followed by the crystallization of GeSe₂. The crystallization process for the Ag-rich glass was more complex with the appearance of a non-identified third phase. Rietveld refinement helped us in studying the evolution of the lattice constants of each phase upon heating.