Experimental and DFT Study of Structural and Optical Properties of Kesterite-Type Cu<Subscript>2</Subscript>ZnSnS<Subscript>4</Subscript> Compound for Solar Cell Applications

In this work, Cu₂ZnSnS₄ (CZTS) thin films were prepared by thermal evaporation from Cu₂SnS₃ and ZnS initially mixed by a mechanical alloying process. Structural and optical properties of CZTS films have been studied. X-ray diffraction results showed that the semiconductor has the Kesterite structure, and the optical absorption coefficient and band gap energy of the thin films were about 10⁴ cm^?1 and 1.46 eV, respectively. The structural and optical properties of Kesterite CZTS, studied by using the full potential linearized augmented plane wave method within the density functional theory, showed good agreement with our experimental results. The surface morphological studies revealed the formation of a smooth, compact and uniform CZTS surface.     

Properties of the Ti<Subscript>40</Subscript>Zr<Subscript>10</Subscript>Cu<Subscript>36</Subscript>Pd<Subscript>14</Subscript> BMG Modified by Sn and Nb Additions

The results of investigation of the influence of additions of 2 and 3 at.% of Sn and simultaneously of Sn and 3 at.% Nb on microstructure and properties of the bulk metallic glasses of composition (Ti₄₀Cu_36?x Zr₁₀Pd₁₄Sn _x )_100?y Nb _y are reported. It was found that the additions of Sn increased the temperatures of glass transition (T _g), primary crystallization (T _x ), melting, and liquidus as well as supercooled liquid range (ΔT) and glass forming ability (GFA). The nanohardness and elastic modulus decreased in alloys with 2 and 3 at.% Sn additions, revealing similar values. The 3 at.% Nb addition to the Sn-containing amorphous phase decreased as well all the T _g, T _x , T _L, and T _m temperatures as ΔT and GFA; however, relatively larger values of this parameters in alloys containing larger Sn content were preserved. In difference to the previously published results, in the case of the amorphous alloys containing small Nb and Sn additions, a noticeable amount of the quenched-in crystalline phases was not confirmed, at least of the micrometric sizes. In the case of the alloys containing Sn or both Sn and Nb, two slightly different amorphous phase compositions were detected, suggesting separation in the liquid phase. Phase composition of the alloys determined after amorphous phase crystallization was similar for all compositions. The phases Cu₈Zr_3, CuTiZr, and Pd₃Zr were mainly identified in the proportions dependent on the alloy compositions.     

Microstructure of YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> subjected to severe plastic deformation by high pressure torsion

The influence of plastic deformation carried out by high pressure torsion at room temperature on the microstructure of the YBa₂Cu₃O _y (123) compound prepared by standard ceramic technology and annealed at low temperature (200°C) in a water-saturated atmosphere has been studied. It has been shown that the directional growth of recrystallized lamellar-shaped grains initiated by the 124–123 phase transformation takes place upon recovery (after deformation) annealing at 930°C in ceramics subjected to additional low-temperature annealing, which leads to the formation of the texture. A rodlike structure has been observed in samples prepared by standard technology, after deformation and recovery annealing (930°C).     

Thermal Spray Deposition,Phase Stability and Mechanical Properties of La<Subscript>2</Subscript>Zr<Subscript>2</Subscript>O<Subscript>7</Subscript>/LaAlO<Subscript>3</Subscript> Coatings

This paper deals with the deposition of La₂Zr₂O₇ (LZO) and LaAlO₃ (LAO) mixtures by air plasma spray (APS). The raw material for thermal spray, single phase LZO and LAO in a 70:30 mol.% ratio mixture was prepared from commercial metallic oxides by high-energy ball milling (HEBM) and high-temperature solid-state reaction. The HEBM synthesis route, followed by a spray-drying process, successfully produced spherical agglomerates with adequate size distribution and powder-flow properties for feeding an APS system. The as-sprayed coating consisted mainly of a crystalline LZO matrix and partially crystalline LAO, which resulted from the high cooling rate experienced by the molten particles as they impact the substrate. The coatings were annealed at 1100 °C to promote recrystallization of the LAO phase. The reduced elastic modulus and hardness, measured by nanoindentation, increased from 124.1 to 174.7 GPa and from 11.3 to 14.4 GPa, respectively, after the annealing treatment. These values are higher than those reported for YSZ coatings; however, the fracture toughness (K _IC) of the annealed coating was only 1.04 MPa m^0.5.     

Effect of hydrogen intercalation on the critical parameters of YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>

The effect of hydrogenation at T = 150 and 200°C on the electrophysical properties of highly textured YBa₂Cu₃O _y ceramics with different oxygen content has been investigated. Like hydration, hydrogenation results in the deterioration of these properties. However, in samples with high oxygen contents (y = 6.96) hydrogenated at T = 150°C after oxidation (400°C) or recovery annealing with subsequent oxidation, the critical current density and first critical field increase compared to the initial state. The improvement of the properties occurs mainly in a magnetic field applied perpendicularly to the c axis. As after hydration, this is connected with the formation of planar defects in the course of low-temperature annealing. In addition, in the process of the hydrogenation, the partial reduction of copper occurs with the formation of microinclusions of Cu₂O and other products of chemical decomposition, which are extra pinning centers of magnetic vortices.     

Influence of water vapor on the formation of pinning centers in YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> upon low-temperature annealing

The influence of the double heat treatment (T = 300 and 930°С) on the critical parameters of highly textured YBa₂Cu₃O_6.96 and YBa₂Cu₃O_6.8 ceramics has been investigated. It has been shown that, upon low-temperature annealing in humid air, planar stacking faults are formed in these ceramics. These defects are partly retained after reduction annealing (at T = 930°С) and are efficient pinning centers in magnetic fields applied parallel and perpendicular to the c axis. Due to the absorption of water, the oxygen content is increased in the ceramics, which is accompanied by an increase in the critical temperature of superconducting transition up to 94 K for YBa₂Cu₃O_6.96 and up to 90 K for YBa₂Cu₃O_6.8. Optimal conditions of the double annealing have been established, after which the critical-current density increased to j _c ≥ 10⁴ А/сm² in an external magnetic field of up to 6 T. The low-temperature treatment in the neutral atmosphere saturated by water vapors deteriorates the current-carrying capacity of the highly textured ceramics, which is connected with the disappearance of texture due to the copper reduction and the precipitation of impurity phases.     

Magnetoresistive properties of Ni-doped La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> manganites

La_0.7Sr_0.3Mn_1?x Ni _x O₃ (x = 0, 0.025, 0.050 and 0.075) ceramics were prepared by the conventional solid-state reaction method. The partial substitution of Mn by Ni²⁺ leads to a decrease in cell volume as well as a structural transition from the rhombohedral to the orthorhombic structure. Ni²⁺ doping increases the electrical resistivity, decreases the semiconductor–metal transition temperature (T _ms) and relatively enhances the room temperature magnetoresistance (MR), especially in x = 0.025 and around T _ms. With respect to conduction mechanism, the small polaron hopping (SPH) and the variable range hopping (VRH) models were used to examine conduction in the semiconducting region.     

Effect of water intercalation on the structure and electrophysical properties of YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>6.9</Subscript>

The influence of water vapors and plastic deformation on the structure and electrophysical properties of YBa₂Cu₃O_6.9 (123) has been studied. It has been established that, at T = 200°C, the introduction of water into the structure of YBa₂Cu₃O_6.9 leads to its transition into a defect tetragonal phase of the 124 type as a result of the formation of planar stacking faults. After annealing at T = 930°C, these defects are partially retained and are efficient centers of pinning in the magnetic fields applied perpendicularly to the c axis, which makes it possible to increase (by an order of magnitude) the critical current density in the high-textured ceramics at 77 K in the external magnetic field of 5–10 T. The plastic deformation of the hydrated ceramics favors the reverse transition of the arising 124 phase to the 123 phase at T = 930°C and is accompanied by a recrystallization of the material, which leads to the appearance of a texture and an increase the critical current density.     

Features of the thermal behavior of PMMA/C<Subscript>60</Subscript> film composites

Polymethylmethacrylate-based film composites containing small additives of fullerenes (up to 3 wt %) are obtained. The thermal behavior of the obtained materials is studied by DSC in the temperature range from 25 to 130°C. It is found that the character of the DSC curve depends on the composite composition. For films containing up to 0.1 wt % C₆₀, one glass transition temperature (T _g ^soft) is observed, while in the case of films with a higher concentration of the filler, two glass transition temperatures (T _g ^soft and T _g ^solid) are observed. It is found that the dependence of T _g ^soft value on the content of fullerenes is nonmonotonic with a minimum at 0.5 wt % of C60.     

Hydrogen storage properties of as-cast and annealed low-Co La<Subscript>1.8</Subscript>Ti<Subscript>0.2</Subscript>MgNi<Subscript>8.9</Subscript>Co<Subscript>0.1</Subscript> alloys

Low-Co La_1.8Ti_0.2MgNi_8.9Co_0.1 alloys were prepared by magnetic levitation melting followed by annealing treatment. The effect of annealing on the hydrogen storage properties of the alloys was investigated systematically by X-ray diffraction (XRD), pressure-composition isotherm (PCI), and electrochemical measurements. The results show that all samples contain LaNi₅ and LaMg₂Ni₉ phases. LaCo₅ phase appears at 1,000 °C. The enthalpy change of all hydrides is close to ?30.6 kJ·mol^?1 H₂ of LaNi₅ compound. Annealing not only increases hydrogen capacity and improves cycling stability but also decreases plateau pressure at 800 and 900 °C. After annealing, the contraction of cell volume and the increase of hydride stability cause the high rate dischargeability to reduce slightly. The optimum alloy is found to be one annealed at 900 °C, with its hydrogen capacity reaching up to 1.53 wt%, and discharge capacity remaining 225.1 mAh·g^?1 after 140 charge–discharge cycles.     

Corrosion Behavior and Microhardness of Ni-P-SiO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Nano-composite Coatings on Magnesium Alloy

In the present work, nano-composites of Ni-P-SiO₂-Al₂O₃ were coated on AZ91HP magnesium alloy. The surface morphology of the nano-composite coating was studied by field emission scanning electron microscopy (FESEM). The amount of SiO₂ in the coating was determined by energy-dispersive analysis of x-ray (EDX), and the crystalline structure of the coating was examined by x-ray diffractometer (XRD). All the experiments concerning the corrosion behavior of the coating carried out in 3.5 wt.% NaCl solution and evaluated by electrochemical impedance spectroscopy (EIS) and polarization technique. The results showed that an incorporation of SiO₂ and Al₂O₃ in Ni-P coating at the SiO₂ concentration of 10 g/Land 14 g/LAl₂O₃ led to the lowest corrosion rate (i _corr = 1.3 µA/cm²), the most positive E _corr and maximum microhardness (496 VH). Furthermore, Ni-P-SiO₂-Al₂O₃ nano-composite coating possesses less porosity than that in Ni-P coating, resulting in improving corrosion resistance.     

Effect of Plastic Deformation on the Formation of the YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> Structure

The structure of the YBa₂Cu₃O _y (123) compound has been investigated after severe plastic deformation by high-pressure torsion performed at room temperature. Distinctive structural features of the samples prepared by standard synthesis and the samples (with increased critical current density) after treatment at t = 200°C in water-saturated atmosphere have been revealed. It has been shown that a lamellar textured structure formed during the annealing of hydrated and deformed samples includes a superconducting orthorhombic phase with a high oxygen index and residual defects that can serve as pinning centers.     

Dependence of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> coating thickness and annealing conditions on microstructural and electrochemical properties of LiCoO<Subscript>2</Subscript> film

We studied the dependence of Al₂O₃ coating thickness and annealing conditions on the surface morphology and electrochemical properties of Al₂O₃ coated LiCoO₂ films. The optimum coating thickness allowing for the highest capacity retention was about 24 nm. A sample consisting of Al₂O₃ coated on annealed LiCoO₂ film with additional annealing at 400 °C had a uniform coating layer between the coating materials and cathode films. This sample showed the best capacity retention of ∼91 % with a charge-cut off of 4.5 V after 30 cycles, while the bare cathode film showed a capacity retention of ∼32 % under the same conditions. The formation of second phases such as Co-Al-O was observed in the coating films by X-ray photoelectron spectroscopy (XPS). The Co-Al-O containing samples showed a higher initial capacity because of their smaller grain size, but less capacity retention than the Al₂O₃ containing samples.     

Synthesis and characterization of Cu2ZnSnS4 thin films grown by PLD: Solar cells

As-deposited and annealed Cu₂ZnSnS₄ (CZTS) thin films have been synthesized onto Mo coated glass substrates at different deposition times using pulsed laser deposition (PLD) technique. The effect of deposition time (film thickness) and annealing onto the structural, morphological, compositional and optical properties of CZTS thin films have been investigated. The polycrystalline CZTS thin films with tetragonal crystal structure have been observed from structural analysis. FESEM and AFM images show the smooth, uniform, homogeneous and densely packed grains and increase in the grain size after annealing. The internal quantitative analysis has been carried out by XPS study which confirms the stoichiometry of the films. The optical band gap of CZTS films grown by PLD is about 1.54 eV, which suggests that CZTS films can be useful as an absorber layer in thin film solar cells. Device performance for deposited CZTS films has been studied.     

Effect of Hydrogen Intercalation on the Structure of YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> with a Low Oxygen Content

We used Raman spectroscopy to study the interaction of YBa₂Cu₃O_y (123) (y ≤ 6.5) with hydrogen at temperatures of 150–200°С. In contrast to the YBa₂Cu₃O_6.96 compound, compositions with low oxygen contents show a lower tendency to form stacking faults. We found that the hydrogenation of these compositions does not lead to the transformation of the 123 phase to the pseudo-124 phase. Absorbed hydrogen does not react with oxygen in 123 and does not form hydroxyl groups. The H_xYBa₂Cu₃O_y oxyhydride is the hydration-reaction product.     

Microstructure and Electron Energy-Loss Spectroscopy Analysis of Interface Between Cu Substrate and Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Film Formed by Aerosol Deposition Method

Aerosol deposition method is a technique to form dense films by impacting solid particles on a substrate at room temperature. To clarify the bonding mechanism between AD films and substrates, TEM observation and electron energy-loss spectroscopy (EELS) analysis of the interface between Al₂O₃ AD films and Cu substrates were conducted. The Al₂O₃ film was directly adhered to the Cu substrate without any void or crack. The film was composed of randomly oriented α-Al₂O₃ crystal grains of about 10-20 nm large. At the Al₂O₃/Cu interface, the lattice fringes of the film were recognized, and no interfacial layer with nanometer-order thickness could be found. EELS spectra near O-K edge obtained at the interface had the pre-peak feature at around 528 eV. According to previously reported experiments and theoretical calculations, this suggests interactions between Cu and O in Al₂O₃ at the interface. It is inferred that not only the anchoring effect but also the ionic bonding and covalent bonding that originates from the Cu-O interactions contribute to the bonding between Al₂O₃ AD films and Cu substrates.     

Microstructure and mechanical properties of multi-principal component AlCoCrFeNiCu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> alloy

By introducing Cu, AlCoCrFeNiCu _x (x values in molar ratio, x = 0, 0.1, 0.5, 1.0, 1.5, 2.0, and 2.5) alloys were designed and prepared. The effects of Cu on microstructure and properties of AlCoCrFeNi alloy were investigated. The introduction of Cu results in the formation of Cu-rich FCC solid solution phase when Cu content is low. There are two FCC solid solution phases, i.e., Cu-rich FCC solid solution phase and phase transformation-induced FCC solid solution phase, when the Cu content is more than 1.0. Both the yield stress and plastic strain of alloy show a turning point when the Cu content is 0.5. Among the seven alloys, Cu_0.5 alloy exhibits the largest yield stress of 1187 MPa and the lowest plastic strain of 16.01 %.     

Effects of defects generated in ALD TiO<Subscript>2</Subscript> films on electrical properties and interfacial reaction in TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript>/Si system upon annealing in vacuum

Thin TiO₂ layers grown at 130°C on SiO₂-coated Si substrates by atomic layer deposition (ALD) using TTIP and H₂O as precursors were annealed, and the effects of the annealing temperature on the resulting electrical properties of TiO₂ and the interface properties between a Pt electrode and TiO₂ were examined using transmission line model (TLM) structures. The as-deposited TiO₂ thin film had an amorphous structure with OH groups and a high resistivity of 6×10³Ω-cm. Vacuum annealing at 700 °C transformed the amorphous film into an anatase structure and reduced its resistivity to 0.04Ω-cm. In addition, the vacuum-annealing of the TiO₂/SiO₂ structure at 700°C produced free silicon at the TiO₂-SiO₂ interface as a result of the reaction between the Ti interstitials and SiO₂. The SiO₂ formed on the TiO₂ surface caused a Schottky contact, which was characterized by the TLM method. The use of the TLM method enabled the accurate measurement of the resistivity of the vacuum-annealed TiO₂ films and the characterization of the Schottky contacts of the metal electrode to the TiO₂.     

Electrochemical Behavior Assessment of Micro- and Nano-Grained Commercial Pure Titanium in H<Subscript>2</Subscript>SO<Subscript>4</Subscript> Solutions

In this study, the electrochemical behavior of commercial pure titanium with both coarse-grained (annealed sample with the average grain size of about 45 µm) and nano-grained microstructure was compared by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and Mott-Schottky analysis. Nano-grained Ti, which typically has a grain size of about 90 nm, is successfully made by six-cycle accumulative roll-bonding process at room temperature. Potentiodynamic polarization plots and impedance measurements revealed that as a result of grain refinement, the passive behavior of the nano-grained sample was improved compared to that of annealed pure Ti in H₂SO₄ solutions. Mott-Schottky analysis indicated that the passive films behaved as n-type semiconductors in H₂SO₄ solutions and grain refinement did not change the semiconductor type of passive films. Also, Mott-Schottky analysis showed that the donor densities decreased as the grain size of the samples reduced. Finally, all electrochemical tests showed that the electrochemical behavior of the nano-grained sample was improved compared to that of annealed pure Ti, mainly due to the formation of thicker and less defective oxide film.     

Multiferroic BiFeO<Subscript>3</Subscript> thick film fabrication by aerosol deposition

BiFeO₃ (BFO) multiferroic materials in the crystalline phase require very delicate processing conditions. In order to fabricate a high quality BFO thick film, aerosol deposition (AD) was employed and the phase evolution and multiferroic properties of the film were investigated for different annealing temperatures. A BFO thick film annealed at 500 °C had a dielectric constant of 80 at 1 kHz and possessed ferroelectric characteristics. At an applied electric field of ∼900 kV/cm, the remaining polarization and coercive field (E_c) were approximately 7.5 μC/cm² and 370 kV/cm, respectively. In addition, the BFO thick film fabricated via AD and annealed at 500 °C showed weak ferromagnetic behavior between −1250 Oe and +1250 Oe and was saturated at the higher magnetic field strength, showing ferromagnetic behavior.