Cadmium telluride for high-efficiency solar cells

Problems of the synthesis of cadmium telluride powders having required purity and grain size distribution for high-efficiency solar cells have been analyzed. A test batch of powders has been synthesized and used for the manufacture and study of thin-film solar cell specimens exhibiting parameters compliant with the best worldwide standards. The phase composition of the powders has been studied using X-ray diffraction. Structural analysis and elemental composition measurements have been carried out using electron microscopy. The effect of free tellurium phase in the powders on the endurance of devices manufactured from the powder has been described. We show that excess tellurium in the film specimens whose atoms are predominantly localized along grain boundaries may cause temporal degradation of the electrical properties of the manufactured solar cells due to changes in the parameters of the crystalline structure of the cadmium telluride phase which are caused in turn by changes in the stoichiometric composition of the material. Structural studies of the film specimens have not revealed differences in the film structure before and after endurance tests. A new cadmium telluride powder process route has been developed, proven and tested taking into account the advantages and drawbacks of the previously used process and experiments confirming the correctness of the technical solutions chosen have been conducted

MXene-containing composite electrodes for hydrogen evolution: material design aspects and approaches for electrode fabrication

This work explores the possibilities for the processing of Ni- and Ti3C2Tx (T = OH, O) MXene-containing composite electrodes, by co-pressing and plastic deformation or by etching of the electrodes prepared directly by self-propagation high-temperature synthesis (SHS). Various material design approaches were also explored. In order to tune the Ti3C2 interlayer distance in Ti3C2Al MAX phase, an introduction of additional Al to form Ti3C2Alz materials with z > 1 was attempted. Self-propagation high-temperature synthesis of powder mixtures with extra Ni and Al content (e.g. Ni:Ti:Al:C = 1:2:3:1) resulted in SHS products containing Ti3C2Alz z > 1 material and Ni–Al alloys. Further etching of these products in 10M NaOH allowed the direct formation of electrodes with active surface containing Ti3C2Tx (T = OH, O) MXene- and Raney nickel-containing composites. The electrochemical studies were focused on hydrogen evolution and showed the potential for boosting the electrochemical reaction in Ni and MXene-containing composite electrodes, especially at high current densities. The guidelines for the processing of such electrodes under fluorine-free conditions are proposed and discussed.publishe

Cadmium telluride for high-efficiency solar cells

Problems of the synthesis of cadmium telluride powders having required purity and grain size distribution for high-efficiency solar cells have been analyzed. A test batch of powders has been synthesized and used for the manufacture and study of thin-film solar cell specimens exhibiting parameters compliant with the best worldwide standards. The phase composition of the powders has been studied using X-ray diffraction. Structural analysis and elemental composition measurements have been carried out using electron microscopy. The effect of free tellurium phase in the powders on the endurance of devices manufactured from the powder has been described. We show that excess tellurium in the film specimens whose atoms are predominantly localized along grain boundaries may cause temporal degradation of the electrical properties of the manufactured solar cells due to changes in the parameters of the crystalline structure of the cadmium telluride phase which are caused in turn by changes in the stoichiometric composition of the material. Structural studies of the film specimens have not revealed differences in the film structure before and after endurance tests. A new cadmium telluride powder process route has been developed, proven and tested taking into account the advantages and drawbacks of the previously used process and experiments confirming the correctness of the technical solutions chosen have been conducted

The Effect of Ce on the Microstructure, Superplasticity, and Mechanical Properties of Al-Mg-Si-Cu Alloy

The current study focuses on the influence of Ce on the superplastic behavior, microstructure, and mechanical properties of the Al-Mg-Si-Cu-Zr-Sc alloy. The multilevel microstructural analysis including light, scanning electron, and transmission electron microscopies was carried out. The simple thermomechanical treatment including the hot and cold rolling resulted in fragmentation of the eutectic originated particles of the Ce-bearing phases. The two-step annealing of the ingots provided the precipitation of the L12-structured Al3(Sc,Zr) phase dispersoids with 10 nm mean size and a high number density. Due to the particle stimulated nucleation (PSN) effect caused by the particles of eutectic origin, and Zener pinning effect provided by nanoscale dispersoids of L12-structured phases, the studied alloy demonstrated good superplastic properties

Structure formation by hot extrusion of thermoelectric bismuth chalcogenide solid solution rods

Major advantage of extruded Bi2Te3 based thermoelectric materials is high mechanical strength compared with that of melt-crystallized materials. Mechanical properties are of special importance for thermogenerator module applications where thermogenerator branches may undergo elevated thermal stresses due to large temperature differences at the modules. Since extrusion is typically a high-temperature process the structure of extruded materials is controlled by the plastic deformation in multiple slip systems resulting in the formation of a final deformed structure. The grain orientations are predominantly such that the most probable cleavage plane orientation is parallel to the extrusion axis. Recovery processes occur simultaneously and different recrystallization stages may take place. In the latter case the deformed texture may be destroyed. Structure evolution along the extruded rod of Bi2Se0.3Te2.7 ternary solid solution was studied with metallography and X-ray diffraction. Extrusion was interrupted for the study and so the specimen was a whole rod the initial part of which was the extrusion billet and the final part was the as-extruded material. The structure of the material is formed by competitive processes of dislocation generation and annealing. The plastic deformation energy is the highest in the extruder zone of the rod. Both the hardening processes and the texture are controlled by the plastic deformation mechanism. Plastic deformation is accompanied by generation of defects that are most likely vacancy type ones

Structure formation by hot extrusion of thermoelectric bismuth chalcogenide solid solution rods

Major advantage of extruded Bi2Te3 based thermoelectric materials is high mechanical strength compared with that of melt-crystallized materials. Mechanical properties are of special importance for thermogenerator module applications where thermogenerator branches may undergo elevated thermal stresses due to large temperature differences at the modules. Since extrusion is typically a high-temperature process the structure of extruded materials is controlled by the plastic deformation in multiple slip systems resulting in the formation of a final deformed structure. The grain orientations are predominantly such that the most probable cleavage plane orientation is parallel to the extrusion axis. Recovery processes occur simultaneously and different recrystallization stages may take place. In the latter case the deformed texture may be destroyed. Structure evolution along the extruded rod of Bi2Se0.3Te2.7 ternary solid solution was studied with metallography and X-ray diffraction. Extrusion was interrupted for the study and so the specimen was a whole rod the initial part of which was the extrusion billet and the final part was the as-extruded material. The structure of the material is formed by competitive processes of dislocation generation and annealing. The plastic deformation energy is the highest in the extruder zone of the rod. Both the hardening processes and the texture are controlled by the plastic deformation mechanism. Plastic deformation is accompanied by generation of defects that are most likely vacancy type ones

Mechanical properties of medium-temperature thermoelectric materials based on tin and lead tellurides

The strength and thermoelectric properties of PbTe and Sn0.9Pb0.1Te medium-temperature polycrystalline specimens with p and n conductivity types, respectively, have been studied. The specimens have been produced using extrusion and spark plasma sintering. The strength parameters of the materials were studied using uniaxial compression at 20 to 500 °C. The structure of the materials was studied using X-ray diffraction and electron microscopy. The electrical conductivity and the Seebeck coefficient were measured simultaneously using the four-probe and differential methods. The temperature conductivity and the specific heat capacity were measured using the laser flash and differential scanning calorimetry methods. The PbTe and Sn0.9Pb0.1Te materials produced using extrusion and spark plasma sintering prove to be single-phase and have homogeneous compositions. For comparable synthesis methods, the dislocation density in the Sn0.9Pb0.1Te specimens is by an order of magnitude lower than in the PbTe ones. Study of the mechanical properties of n and p conductivity type specimens over a wide temperature range from 20 to 500 °C has shown that their deformation is plastic and has no traces of brittle fracture. For these plastic materials, the strength criterion has been accepted to be the arbitrary yield stress corresponding to the stress at a 0.2% deformation. The 20 °C yield stress of PbTe and Sn0.9Pb0.1Te is far higher for the specimens produced by extrusion. For all the test temperatures and synthesis methods the Sn0.9Pb0.1Te specimens have a higher strength than the PbTe ones. The PbTe and Sn0.9Pb0.1Te specimens produced by extrusion have better thermoelectric properties than the spark plasma sintered ones. The heat conductivity of the PbTe and Sn0.9Pb0.1Te specimens is almost the same regardless of compaction method

Structural properties of the formation of zinc-containing nanoparticles obtained by ion implantation in Si (001) and subsequent thermal annealing

This work deals with the study of structural transformations in the near-surface layers of silicon after ion beam synthesis of zinc-containing nanoparticles. Phase formation after implantation of Zn+ ions and two-stage implantation of O+ and Zn+ ions with subsequent thermal annealing in an atmosphere of dry oxygen has been considered. We heated the substrate to 350 °C during the implantation to avoid amorphization. After implantation, the specimens were annealed for 1 h in a dry oxygen atmosphere at 800 °C. Investigation of the structure of surface silicon layers has been carried out by X-ray diffractometry and transmission electron microscopy. We show that a damaged layer with a large concentration of radiation induced defects forms near the surface as a result of the implantation of Zn+ ions with an energy of 50 keV. In the as-implanted state, nanoparticles of metallic Zn with a size of about 25 nm form at a depth of 40 nm inside the damaged silicon layer. Subsequent annealing at 800 °C in a dry oxygen atmosphere leads to structural changes in the defect layer and the formation of Zn2SiO4 nanoparticles at a depth of 25 nm with an average size of 3 nm, as well as oxidation of the existing Zn particles to the Zn2SiO4 phase. The oxidation of the metallic Zn nanoparticles starts from the surface of the particles and leads to the formation of particles with a “core-shell” structure. Analysis of the phase composition of the silicon layer after two-stage implantation with O+ and Zn+ ions showed that Zn and Zn2SiO4 particles form in the as-implanted state. Subsequent annealing at 800 °C in a dry oxygen atmosphere leads to an increase in the particle size but does not change the phase composition of the near-surface layer. ZnO nanoparticles were not observed under these experimental conditions of ion beam synthesis

Regularities of Structure Formation in 30 mm Rods of Thermoelectric Material during Hot Extrusion

In this study, Ingots of (Bi, Sb)2Te3 thermoelectric material with p-type conductivity have been obtained by hot extrusion. The main regularities of hot extrusion of 30 mm rods have been analyzed with the aid of a mathematical simulation on the basis of the joint use of elastic-plastic body approximations. The phase composition, texture and microstructure of the (Bi, Sb)2Te3 solid solutions have been studied using X-ray diffraction and scanning electron microscopy. The thermoelectric properties have been studied using the Harman method. We show that extrusion through a 30 mm diameter die produces a homogeneous strain. The extruded specimens exhibit a fine-grained structure and a clear axial texture in which the cleavage planes are parallel to the extrusion axis. The quantity of defects in the grains of the (Bi, Sb)2Te3 thermoelectric material decreases with an increase in the extrusion rate. An increase in the extrusion temperature leads to a decrease in the Seebeck coefficient and an increase in the electrical conductivity. The specimens extruded at 450 °C and a 0.5 mm/min extrusion rate have the highest thermoelectric figure of merit (Z = 3.2 × 10−3 K−1)

Effect of σ-Phase on the Strength, Stress Relaxation Behavior, and Corrosion Resistance of an Ultrafine-Grained Austenitic Steel AISI 321

This paper reported the results of research into the effect of Equal Channel Angular Pressing (ECAP) temperature and 1-h annealing temperature on mechanical properties, stress-relaxation resistance, and corrosion resistance of austenitic steel AISI 321L with strongly elongated thin δ-ferrite particles in its microstructure. The formation of α′-martensite and fragmentation of austenite grains takes place during ECAP. Ultrafine-grained (UFG) steels demonstrate increased strength. However, we observed a reduced Hall–Petch coefficient as compared with coarse-grained (CG) steels due to the fragmentation of δ-ferrite particles. UFG steel specimens were found to have 2–3 times higher stress-relaxation resistance as compared with CG steels. For the first time, the high stress-relaxation resistance of UFG steels was shown to stem from a internal stress-relaxation mechanism, i.e., the interaction of lattice dislocations with non-equilibrium grain boundaries. Short-time 1-h annealing of UFG steel specimens at 600–800 °C was found to result in the nucleation of σ-phase nanoparticles. These nanoparticles affect the grain boundary migration, raise strength, and stress-relaxation resistance of steel but reduce the corrosion resistance of UFG steel. Lower corrosion resistance of UFG steel was shown to be related to the formation of α′-martensite during ECAP and the nucleation of σ-phase particles during annealing