Characterization of (Ti1−xAlx)N films prepared by radio frequency reactive magnetron sputtering

(Ti_1−xAl_x)N films were deposited by radio frequency reactive magnetron sputtering on a high speed steel substrate. The structure and composition of the coatings were analysed by various techniques. Hardness and adhesion of the films were investigated using Vickers micro-indentation and scratch test respectively, whereas their tribological properties were studied using a pin-on-disk tribometer. The results show that increasing aluminium content leads to increase hardness of the films and to decrease their wear resistance when sliding against a magnesia-stabilized zirconia ball. On the contrary, no clear dependence of the film adhesion on the aluminium concentration was detected.     

Optical scattering of nanocrystalline Pb(ZrxTi1−x)O3 films

Optical characterization methods, like spectrophotometry at UV–vis-NIR wavelengths and prism-coupler method, were applied to polycrystalline Pb(Zr_xTi_1?x)O₃ thin films at various thicknesses. Thin films were deposited at room temperature by pulsed laser deposition on MgO (1 0 0) substrates and post-annealed at different temperatures. X-ray diffraction and atomic force microscopy were used to characterize the crystal structure and surface morphology of the thin films, respectively.Well oscillating transmission with a sharp fall near the absorption edge was found in films with high orientation and low surface roughness. Changes in the surface morphology and crystal orientation were found to modulate optical interference maxima and minima of the transmittance spectra and to increase the width of the TE₀ mode (Δβ ≈ 0.06) indicating an increase in the scattering losses of the films. Single-phase oriented films had sharpest coupling values (Δβ ≈ 0.005) of the TE₀ mode.     

Photo-electrochemical performance of Cd1−xPbxS (0≤x≤1) thin films

This paper discusses chemical synthesis of Cd_1?xPb_xS (0≤x≤1) thin film layers and their photo-electrochemical properties with special reference to PEC parameters. Previously optimized conditions were used for the deposition. The electrode/electrolyte interfaces were then formed between the Cd_1?xPb_xS thin film layers and a sulphide/polysulphide (1 M) redox couple and investigated through the various photo-electrochemical (PEC) properties to assess suitability to convert solar energy into electrical energy.Increase in short circuit current (I_sc) and open circuit voltage (V_oc) was observed with increased composition and attain maximum at x=0.175. Power conversion efficiency and fill factor were found to be 0.163% and 46.2% respectively for the composition parameter x=0.175.     

Preparation of Y1−x Yb x Ba2Cu3O7−y superconducting films by chemical vapor deposition

High Tc Y_1−x Yb _x Ba₂Cu₃O_7−y films were prepared on SrTiO₃(100) substrates by chemical vapor deposition method. Yb₁Ba₂Cu₃O_7−y films were obtained at higher oxygen partial pressure compared with Y₁Ba₂Cu₃O_7−y films at the same deposition temperature. Tc,o (R=0) decreased about 1.5 K when Y was fully substituted with Yb. The caxis lattice parameter of Y_1−x Yb _x Ba₂Cu₃O_7−y films also decreased as the amount of Yb(x) increased.     

Surface Exchange of Oxygen in La1−x Sr x FeO3−δ (x = 0, 0.1)

The electronic charge carrier concentration in La_1?x Sr _x FeO_3?δ was shown to depend on the partial pressure of O₂ (pO ₂). Chemical diffusion coefficient and surface exchange coefficient, k _chem, were determined by conductivity relaxation in O₂/N₂ and CO/CO₂ mixtures. k _chem was proportional to pO ₂ ^1.06 in O₂/N₂, while in CO/CO₂ k _chem was controlled by a reaction mechanism involving both CO and CO₂.     

Dielectric and piezoelectric properties of (1−x)(Bi,Na)TiO3–x(Bi,K)TiO3 lead-free ceramics for piezoelectric energy harvesters

The piezoelectric and dielectric properties of the (1−x)(Bi,Na)TiO₃–x(Bi,K)TiO₃ (x=0.12, 0.14, 0.18, 0.20 and 0.30) lead-free ceramics were investigated. Specimens were prepared by the conventional mixed oxide method and sintered at 1170 °C in air. Scanning electron microscopy indicated that increasing x from 0.12 to 0.30 causes a decrease in the grain size. The (1−x)(Bi,Na)TiO₃–x(Bi,K)TiO₃ ceramics shows a homogeneous microstructure and excellent dielectric and piezoelectric properties. Specimens with optimum composition showed a piezoelectric charge constant d₃₃ of 166 pC/N, an electromechanical coupling factor k_p of 0.5, a dielectric constant ε_r of 1591.32 at 1 kHz and generated power output of 37.49 nW/cm².     

Preparation of Bi1−xSbx films by electrodeposition

A method has been developed to produce composition modulated Bi_1–x Sb _x alloys by electrodeposition. The electrolyte which consists of NaCl 4 M and HCl 1 M (pH 0) in aqueous medium, allows codeposition of bismuth and antimony to be accomplished at room temperature on glassy carbon. The composition of the films, their crystal structure, morphology and resistivity were studied as a function of electrochemical parameters and bath composition. It is shown that the electrodeposits are monophasic and exhibit a polycrystalline state. The obtained alloys represent a continuous series of solid solution. The film composition is dependent on the applied current density. The electrical resistivity is of the order of 3–7 m.     

Preparation and electrical properties of (1−x)SrBi2Nb2O9−xBiFeO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics, (1−x)SrBi₂Nb₂O₉−xBiFeO₃ [(1−x)SBN−xBFO] (x=0.0, 0.03, 0.05, 0.07, 0.10) were prepared by a conventional solid-state reaction method. The crystal structure, microstructure and electrical properties were systematically investigated. All compositions formed layered perovskite structure without any detectable secondary phases. Plate-like morphology of the grains which is characteristic for layer-structure Aurivillius compounds was clearly observed. The excellent electrical properties (e.g., d₃₃~19 pC/N, 2P_r~18.8 μC/cm²) and a high Curie temperature (e.g., T_c~449 °C) were simultaneously obtained in the ceramics with x=0.05. Additionally, thermal annealing studies indicated that the BFO modified SBN ceramics system possessed stable piezoelectric properties, demonstrating that the modified SBN-based ceramics are the promising candidates for high-temperature applications.     

Visible-light-responsive photocatalysts xBiOBr–(1−x)BiOI

A new class of oxyhalide photocatalysts xBiOBr–(1−x)BiOI prepared by a soft chemical method were characterized by X-ray diffraction and UV–Vis diffuse reflectance spectra. They are all visible-light-responsive materials with the bandgaps ranging from 1.92 to 2.91 eV. Methyl orange (MO) photocatalytic degradation experiments showed that BiOBr possessed a higher photocatalytic activity than P25 (TiO₂) under UV illumination and iodine-modified BiOBr exhibited high photocatlytic activities under visible-light irradiation. The high photocatalytic activity is in close relation with the deep valance band edge position and the internal electric fields between [Bi₂O₂] slabs and halogen anionic slabs.     

Microwave dielectric properties of the (BaxSr1−x)TiO3 thin films on alumina substrate

Barium strontium titanate, (Ba_xSr_1?x)TiO₃ (BST) thin films have been prepared on alumina substrate by sol–gel technique. The X-ray patterns analysis indicated that the thin films are perovskite and polycrystalline structure. The interdigital electrode with 140 nm thickness Au/Ti was fabricated on the film with the finger length of 80 μm, width of 10 μm and gaps of 5 μm. The temperature dependence of dielectric constant of the BST thin films in the range from ?50 °C to 50 °C was measured at 1 MHz. The dielectric properties of the BST thin films were measured by HP 8510C vector network analyzer from 50 MHz to 20 GHz.     

Ferroelectric–relaxor crossover characteristics in Ba(ZrxTi1−x)O3 ceramics investigated by AFM-piezoresponse study

Ba(Zr_xTi_1?x)O₃ ceramics with x = 0.10 and 0.18 prepared via solid state, with high-density, homogeneous microstructures and similar grain size were investigated. The dielectric data showed that the relaxor properties are induced by increasing the Zr vs. Ti fraction x, both compositions showing a combined relaxor–ferroelectric character. The AFM-piezoresponse experiments revealed a few interesting characteristics, as follows: (1) none of the samples could be totally poled or switched, like the normal ferroelectrics; (2) the samples locally present different types of responses (ferroelectric with a strong piezoresponse, field-induced ferroelectric, polar but non-switchable and non-polar regions); (3) both the regions with a natural strong piezoresponse and the ones obtained after poling are larger in size and more stable in time for the sample with x = 0.10 than for x = 0.18; (4) the sample having x = 0.18 has a smaller piezoresponse than the one with x = 0.10. The observed local features are confirming the ferroelectric–relaxor crossover with increasing x, as observed by the analysis of the dielectric data.     

Dielectric properties of compositionally graded Ba1−xLaxTi1−x/4O3 thick films

Compositionally graded thick films based on lanthanum-substituted barium titanate solid solutions Ba_1−xLa_xTi_1−x/4O₃ (BLT, x=0.02, 0.04, 0.06) are prepared by tape casting and their phase structures, surface morphologies, dielectric and tunability properties have been examined. Compared with single-layered BLT film, compositionally graded BLT02/04/06 film with three-layered sandwich-structure has better temperature stability in dielectric and tunability properties. Curie peak is broadened, dielectric loss is reduced, and more importantly, it has moderate permittivity and high tunability (>35%) in a temperature range of 25–75 °C, which is beneficial for practical applications of tunable devices.     

Magnetic properties of ferrites-cobaltites Bi1 − x La x Fe1 − x Co x O3 (1.0 ≥ x ≥ 0.7) with a perovskite structure

The molar magnetic susceptibility (χ_mol) of Bi_{1 ? x} La _x Fe_{1 ? x} Co _x O₃ solid solutions (x = 1.0, 0.9, 0.8, or 0.7) with a crystal structure of rhombohedrally distorted perovskite (R $\bar 3$ c) has been investigated in the temperature range of 5–300 K in a 0.86 T magnetic field. In the temperature range where χ_mol depends on temperature T according to the Curie-Weiss law, the resulting effective magnetic moments of Fe³⁺ and Co³⁺ ions ( $\mu _{eff,Fe^{3 + } ,Co^{3 + } ,} \mu _{eff,Fe^{3 + } } $ and $\mu _{eff,Co^{3 + } } $ ) have been determined for the solid solutions under study. Fe³⁺ ions in the solid solutions have been found to be in the mixed intermediate spin (IS) and high spin (HS) states ( $\mu _{eff,Fe^{3 + } } $ is 4.26μ_B and 4.68μ_B for the temperature range of 5–100 and 150–300 K, respectively). It is shown that 8% Co³⁺ ions in LaCoO₃ at 5–19 K are in the paramagnetic IS state and they determine to a great extent the magnetic susceptibility. It is established that only 9% and 18% Co³⁺ ions in Bi_{1 ? x} La _x Fe_{1 ? x} Co _x O₃ solid solutions (x = 0.9 or 0.8) are in the paramagnetic IS state in the temperature ranges of 5–30 and 5–110 K, respectively, while the other ions are diamagnetic.     

Structural and ion transport properties of [(AgI)x(AgBr)0.4−x](LiPO3)0.6 and (AgBr)x(LiPO3)(1−x) solid electrolytes

The (AgBr)_x(LiPO₃)_(1−x) (x=0.4 and 0.5) and [(AgI)_x(AgBr)_0.4−x](LiPO₃)_0.6 (x=0.1, 0.2, and 0.3) superionic electrolytes have been prepared by conventional melt quenching using a twin roller. These electrolytes are characterized by X-ray diffraction, SEM, and energy dispersive X-ray analysis (EDAX) for structural investigation. Electrical characterizations have been carried out by the AC impedance analysis. The conductivity of LiPO₃ glassy system at room temperature is improved by doping with the silver bromide (AgBr)_x(LiPO₃)_(1−x) and the mixture of silver iodide, silver bromide (AgI-AgBr-LiPO₃ system) up to 10⁻⁵ and 10⁻³ Ω⁻¹ cm⁻¹, respectively (improvements by four or five orders of magnitude). The frequency response of ionic conductivity has been analyzed by universal dynamic response model (Jonscher's law) and AC conductivity data are fitted using the Jonscher's power law. The conductivity values obtained by the power law and impedance plots are comparable. The frequency exponent (n) has a value between 0 and 1. The AgI-AgBr-LiPO₃ system shows the mixed alkali effect. Summerfield scaling master curve is temperature dependent, which may be due to the contribution of the both lithium and silver ions to ionic conduction.     

Density and surface tension of Se(90−0.9x )S(10−0.1x)Me x and Se(60−0.6x)S(40−0.4x)Me x (Me = Sb), Ge glass-forming meltsMe x (Me = Sb), Ge glass-forming melts

The properties of melts in the Se_(90−0.9x)S_(10−0.1x)Me _x and Se_(60−0.6x)S_(40−0.4x)Me _x (Me = Sb, Ge) systems (wherex ranges from 2.5 to 15 mol % with a step of 2.5 mol %) have been investigated. The density and surface tension of melts and the wetting angles of the PbSe semiconductor by melts are measured. The work of adhesion and adhesion strength of the glass coating are calculated. The experimental data are processed using the least-squares method, and the corresponding regression equations are derived. From the materials of the paper reported at the International Conference “Glasses and Solid Electrolytes” (St. Petersburg, 1999, May 17–19).     

Structural investigation of substoichiometry and solid solution effects in Ti2Al(Cx,N1−x)y compounds

The milling, cold compaction and thermal annealing (4 h–1400 °C–Ar flow) of Ti, TiC, Al and AlN powders were used to produce Ti₂Al(C_xN_(1?x))_y compounds with x = 0, 0.25, 0.5, 0.75, 1 and 0.7 ≤ y ≤ 1. X-ray diffraction analysis, scanning electron microscopy observations combined with microanalysis confirmed the formation of the almost pure Ti₂AlC_xN_(1?x) carbonitrides for y = 1 whereas increasing amounts of titanium aluminides were formed when y decreases. Proportions of the different phases deduced from Rietveld refinements of the X-ray diffractograms indicate that no or very poor substoichiometry in carbon was possible in carbide whereas C and N deficiency can be achieved in nitrides and carbonitrides Ti₂AlC_xN_(1?x). Electron Energy Loss Spectroscopy investigations confirm that carbonitrides can have at least 20% of vacancies on the C or N site. The a lattice parameter varies linearly with x whereas it is not the case for the c lattice parameter, its values being lower for the carbonitrides. Furthermore, a strong broadening of the carbonitrides’ XRD peaks is observed, a phenomenon that can be mainly attributed to C and N concentration gradients inside the samples.     

Microstructural evolution of Si(HfxTa1−x)(C)N polymer-derived ceramics upon high-temperature anneal

Ultra-high temperature ceramic nanocomposites (UHTC-NC) within the Si(Hf_xTa_1?x)(C)N system were synthesized via the polymer-derived ceramics (PDC) synthesis route. The microstructure evolution of the materials was investigated upon pyrolysis and subsequent heat treatment. The crystallization behavior and phase composition were studied utilizing X-ray diffraction, scanning- and transmission electron microscopy. Single-source-precursors were converted into amorphous single-phase ceramics, with the exception of surface crystallization effects, at 1000 °C in NH₃. Annealing in N₂ at 1600 °C resulted in fully crystalline UHTCs. The powder samples revealed microstructures consisting of two characteristic regions, bulk and surface; displaying intrinsic microstructure and phase composition differences. Instead of the expected nitrides, transition metal carbides (TMC) were detected upon high-temperature anneal. The residual carbon available in the system triggered a decomposition reaction, resulting in the formation of TMCs plus gaseous nitrogen and SiC. Experimental data underline that N-containing PDCs are prone to phase separation accompanied by thermal decomposition and diffusion-controlled coarsening.     

New scheelite-type Cd1−3x⌷xGd2x(MoO4)1−3x(WO4)3x ceramics – their structure,thermal and magnetic properties

Polycrystalline samples of scheelite-type Cd_1−3x⌷_xGd_2x(MoO₄)_1−3x(WO₄)_3x solid solution with limited homogeneity (0<x≤0.25) and cationic vacancies (denoted as ⌷) have successfully prepared by a high-temperature annealing of CdMoO₄/Gd₂(WO₄)₃ mixtures composed of 50.00 mol% and less of gadolinium tungstate. Initial reactants and obtained ceramic materials were characterized by XRD, simultaneous DTA–TG, and SEM techniques. A phase diagram of the pseudobinary CdMoO₄–Gd₂(WO₄)₃ system was constructed. The eutectic point corresponds to 1404±5 K and ~70.00 mol% of gadolinium tungstate in an initial CdMoO₄/Gd₂(WO₄)₃ mixture. With decreasing of Gd³⁺ content in a CdMoO₄ framework, the melting point of Cd_1−3x⌷_xGd_2x(MoO₄)_1−3x(WO₄)_3x increases from 1406 (x=0.25) to 1419 K (x=0.0833), and next decreases to 1408 K (x=0). EPR method was used to identify paramagnetic Gd³⁺ centers in Cd_1−3x⌷_xGd_2x(MoO₄)_1−3x(WO₄)_3x for different values of x parameter as well as to select biphasic samples containing both Cd_0.25⌷_0.25Gd_0.50(MoO₄)_0.25(WO₄)_0.75 and Gd₂(WO₄)₃.