Antistructure Defects Research Articles

Defect Emission and Its Dipole Orientation in Layered Ternary Znln2 S4 Semiconductor.

Defect engineering is promising to tailor the physical properties of 2D semiconductors for function-oriented electronics and optoelectronics. Compared with the extensively studied 2D binary materials, the origin of defects and their influence on physical properties of 2D ternary semiconductors are not clarified. Here, the effect of defects on the electronic structure and optical properties of few-layer hexagonal Znln2 S4 is thoroughly studied via versatile spectroscopic tools in combination with theoretical calculations. It is demonstrated that the Zn-In antistructural defects induce the formation of a series of donor and acceptor energy levels and sulfur vacancies induce donor energy levels, leading to rich recombination paths for defect emission and extrinsic absorption. Impressively, the emission of donor-acceptor pair in Znln2 S4 can be significantly tailored by electrostatic gating due to efficient tunability of Fermi level (Ef ). Furthermore, the layer-dependent dipole orientation of defect emission in Znln2 S4 is directly revealed by back focal plane imagining, where it presents obviously in-plane dipole orientation within a dozen-layer thickness of Znln2 S4 . These unique features of defects in Znln2 S4 including extrinsic absorption, rich recombination paths, gate tunability, and in-plane dipole orientation are definitely a benefit to the advanced orientation-functional optoelectronic applications.

Application of radio spectroscopy methods for the study of thermoelectrics with a chalcopyrite structure

Doped chalcopyrite compounds are considered. The results of studying the spectral parameters by the 63,65Cu NMR method in a local field, as well as by the EPR method in the temperature range 15-300 K are presented. The observed broadening of the resonance lines of the NMR spectra and the detection of a paramagnetic signal in the sample at a temperature of 15 K indicate the appearance of anti-structural defects. The rapid change in the shape of the EPR spectrum line, in the temperature range 100-130 K, is associated with the structural-phase transition. Keywords: thermoelectrics, chalcopyrite compounds, antisite defects.

Application of radio spectroscopy methods for the study of thermoelectrics with a chalcopyrite structure

Doped chalcopyrite compounds are considered. The results of studying the spectral parameters by the 63,65Cu NMR method in a local field, as well as by the EPR method in the temperature range 15-300 K are presented. The observed broadening of the resonance lines of the NMR spectra and the detection of a paramagnetic signal in the sample at a temperature of 15 K indicate the appearance of anti-structural defects. The rapid change in the shape of the EPR spectrum line, in the temperature range 100-130 K, is associated with the structural-phase transition. Keywords: thermoelectrics, chalcopyrite compounds, antisite defects.

Local Structure and Anti-Structural Defects of Tin in Amorphous and Crystalline Ge2Sb2Te5 Films

The absorption Mossbauer spectroscopy on 119Sn impurity centers shows that germanium atoms in the structure of amorphous and polycrystalline Ge2Sb2Te5 films have different local symmetries (tetrahedral in the amorphous phase and octahedral in the crystalline). By emission Mossbauer spectroscopy on 119mSn impurity centers formed after the radioactive decay of 119Sb or 119mTe parent atoms, tin antisite defects at antimony and tellurium sites of crystalline Ge2Sb2Te5 films are identified.

A 63,65Cu NMR Study of Cu1–XPdxFeS2 Chalcopyrite Compounds

A 63,65Cu NMR study was carried out on a series of Cu1–xPdxFeS2 compounds (x = 0–0.02) in a local magnetic field at 77 K. The spectra of the samples were taken. Their parameters were determined and the fields in the region of 63,65Cu nuclei were estimated. Asymmetric broadening of the NMR resonance lines was found along with a smoother decay in the high-frequency region, which may result from an increase in the amount of defects in the crystal lattice of the compound. These can be FeCu2+ antistructural defects, whose formation is attributed to the generation of the PdS phase in the chalcopyrite matrix with an increase in the nominal Pd content.

SMALL-ANGLE SCATTERING OF NEUTRONS ON Sr<sub>2</sub>FeMoO<sub>6–δ</sub> SAMPLES WITH DIFFERENT-DEGREE SUPERSTRUCTURAL ORDERING OF Fe/Mo CATIONS

Single-phase Sr2FeMoO6-δ samples with different-degreesuperstructiral ordering Fe/Mo cations superstructural ordering (P, 76, 86 and 93 %) were obtained by the solid-phase technique. Based on the results of measuring the magnetic characteristics in the samples, we found that an increase in magnetization (26.41, 32.36 and 42.66 A·m2·kg–1), magnetic moment (1.33, 3.07 and 3.58 μB/f.u.) and Curie temperatures (422, 428 and 437 K) withparameter P (76, 86 and 93 %) can be explained by the presence of antistructural defects, as well as antiferromagnetic inclusions. This determines the redistribution of electron density, which is accompanied by the change in electronic configuration of a part of Fe/Mo cations. Based on the temperature dependences of the magnetic moment of the samples measured in ZFC and FC modes, and on small-angle polarized neutron scattering (SANS), we found that the samples are in a magnetically inhomogeneous state. An important result to mention is that we detected the difference between the slope of the SANS curves of samples with different oxygen content, which demonstrates a different microstructure of inhomogeneities. The main inhomogeneities are magnetic inclusions with the dimensions depending on the superstructural ordering of Fe/Mo cations. According to the Porod law, it was shown that the Sr2FeMoO6-δ samples with wave vector values 0.1 > q > 0.002 Å–1 contain polydisperse grains with a smooth surface. For q > 0.1 Å–1 a deviation from the Porod law is observed, confirming the presence of magnetic inhomogeneities with a diameter < 6 nm in the grains.

The influence of cation ordering and oxygen nonstoichiometry on magnetic properties of Sr2FeMoO6–x around Curie temperature

Sr2FeMoO6–x polycrystalline samples with different oxygen content (6−x) and various degrees of superstructural ordering of Fe/Mo cations (P) were obtained by the solid-phase method from the SrFeO2.52 and SrMoO4 precursors. From the investigation on the influence of oxygen non-stoichiometry and the P parameter on the magnetic properties of Sr2FeMoO6–x, it was found that with an increase in P and a decrease in the (6−x) value from 5.99 to 5.94, an increase in the magnetization values is observed in the temperature range 77–600 K. For all the Sr2FeMoO6–x samples there is a tendency that P value rises with increasing x, where, accordingly, the volume fraction of regions in which there are no anti-structural defects increases as well. This is also indicated by Mössbauer spectroscopy data, confirming an increase in the area of the S1 sextet corresponding to Fe ions in highly ordered regions and a decrease in the area of the S2 sextet associated with disordered regions. Using the temperature scanning method, the temperatures of the onset and completion of the transition from the paramagnetic to the ferrimagnetic state and, correspondingly, the blurring width of the transition have been estimated. It turned out that with decreasing P, the blurring of the transition increases, which is associated with an increase in the concentration of anti-structural defects.

Antistructural Defects in Ge–Te, As–Te, and Ge–As–Te Vitreous Alloys

Emission Mossbauer spectroscopy on 119mmSn(119mSn), 119Sb(119mSn), 119mTe(119mSn), 125mTe(125Te), 125Sb(125Te), 125Sn(125Te), and 129mTe(129I) isotopes is used as a method for the creation and identification of antistructural defects in Ge20Te80, As30Te70, and Ge15As4Te81 vitreous alloys in forms of tin atoms in tellurium and arsenic positions, as well as tellurium atoms in germanium and arsenic positions. Tin atoms in the positions of arsenic and tellurium, and tellurium atoms in the positions of germanium and arsenic rearrange their local environment, while the symmetry of the local environment of germanium positions remains unchanged in the case of their isovalent replacement by tin atoms.

Back Cover: Enhanced Electrochemical Performance of Ti‐Doping Li1.15Ni0.47Sb0.38O2 as Lithium‐excess Cathode for Lithium‐ion Batteries (Chin. J. Chem. 12/2017)

The back cover picture shows X‐ray near edge absorption spectroscopy has been applied to cathode materials for lithium‐ion batteries to explore its structure‐activity relationship. The result shows that in the Li‐rich cathode Li1.15Ni0.47Sb0.38O2, as a model system, Ti ions replaced the Li ions and then made an antistructure defect. It would change our understanding to the doped method for the cathode layer materials and benefit for designing other more powerful cathodes. In the picture, the road has been represented by the curve shape of the XANES of the as‐studied sample. The atomic arrangement around the Ti ion of the sample has been put into the tank position of the car. NSRL, National Synchrotron Radiation Laboratory, is the name of our laboratory. More details are discussed in the article by Chu et al. on page 1853–1860. image

Research of physicochemical properties and structure of strongly doped LiNbO3:ZnO ([ZnO] ~ 4.02–8.91 mol %) crystals

In LiNbO3:ZnО crystals grown from melts containing ~4.0–9.0 mol % ZnO, the evolution of structure was studied, the lattice periods were detected, and the models of atomic structure were analyzed. Raman spectroscopy and full-profile analysis of XRD patterns were used to obtain the results. The rise in ZnO concentration in the melt from 4.0 to ~6.99 mol % leads to the decrease in the unit cell volume of the crystals. The further rise in ZnO concentration in the melt to ~7.8 mol % results in the increase in the unit cell volume of the crystals. Refinement of the profile characteristics of XRD patterns and structural characteristics of the researched crystal samples was performed by the Rietveld method using the PDWin software package. All samples were considered single-phase, taking into consideration the absence of intense bands coinciding with the lithium niobate bands. Zn2+ cations were detected to occupy Li sites (which are vacant in the congruent LiNbO3 crystal). In this case, Nb vacancies are absent. Zinc displaces all excess Nb atoms in Li sites. In the sample grown from melt with ~6.12 mol % ZnO. In this case, Li vacancies and electroneutrality stay the same in the sample. Thus, NbLi antistructure defects are absent in the LiNbO3:ZnО crystal (~6.12 mol % ZnО in the melt). In LiNbO3:ZnО crystals with higher ZnO concentration, NbLi antistructure defects appear again. In this case, the concentration of Zn in Li sites almost coincides with the one in the LiNbO3:ZnО crystal. Unit cell parameters are equal in crystals grown from melts with ~7.8 and ~6.76 mol %. The biggest changes in the Raman spectra of these crystals are observed in the regions of vibrations of cations (200–300 cm–1) located in oxygen octahedra ВО6 (В: Nb5+, Li+, Zn2+) and in the region of vibrations of oxygen atoms in oxygen octahedra (500–900 cm–1). This indicates a change in order of alteration of intrinsic, doping cations and vacancies along the polar axis and deformation of oxygen octahedra during doping. This corresponds to anisotropic expansion of oxygen octahedra along the polar axis in LiNbO3:ZnО crystals.

Molecular dynamics study of self-radiation damage in mineral matrices

Mechanisms of radiation damages in minerals promising for the utilization of highly active radioactive waste (zircon ZrSiO4, monazite LaPO4, orthophosphate YbPO4, lakargiite CaZr0,8Sn0,1Ti0,1O, and Gd2Zr2O7 and Gd2Ti2O7 compounds with the pyrochlore structure) are studied by the computer simulation using the molecular dynamics method. The formation of a damaged region in the structures under study is considered along with the recovery (relaxation) processes in these structures. The number of Frenkel pairs and antistructural defects that form in the structure of these minerals after the pass of the knocked out thorium atom is calculated by the molecular dynamics method. A parameter is proposed that characterizes the mineral tendency to amorphization under the effect of the radiation damage. The obtained results show that one of the main factors determining the radiation stability of minerals is the crystal structure type, compounds with the monazite structure being more radiationally stable than compounds with the zircon structure. It is found that the Gd2Zr2O7 compound and lakargiite have a weaker tendency to amorphization than other minerals such as zircon, monazite, and orthophosphate YbPO4. A high radiation stability of the studied Gd2Zr2O7 compound as well as a solid solution of the composition CaZr0.8Sn0.1Ti0.1O3 makes it possible to propose them as a possible matrix for the utilization of highly active radioactive waste.

Evaluation of stability region for scandium-containing rare-earth garnet single crystals and their congruent-melting compositions

Single crystals of scandium-containing rare-earth garnets in system R-Sc-C-O (R3+=Y, Gd; C3+=Al, Ga) have been grown by the Czochralski technique. X-ray diffraction analysis has been used to refine crystal compositions. The fundamental difference between the melt compositions and compositions of grown crystals has been found (except for compositions of congruent-melting compounds, CMC). The specific features of garnet solid solution formation have been established and the ternary diagrams with real or hypothetical phases have been built. The dinamics of coordination polyhedra changes with the formation of substitutional solid solutions have been proposed based on the mathematical modeling and experimental data. Possible existence of CMC with garnet structure in different systems as well as limit content of Sc ions in dodecahedral and octahedral sites prior to their partial substitution of ions, located in other sites, have been evaluated. It was established that the redistribution of cations over crystallographic sites (antistructural point defects) due to system self-organization to maintain its stability may be accompanied by cation ordering and the symmetry change of individual polyhedrons and/or the whole crystal.

Thermoelectric Properties of Highly Deformed and Subsequently Annealed p-Type (Bi0.25Sb0.75)2Te3 Alloys

The effects of mechanical deformation and subsequent annealing on the thermoelectric properties and microstructure have been investigated for p-type (Bi0.25Sb0.75)2Te3 alloys prepared by melting followed by quenching. The mechanically deformed pellets were prepared by repetition of cold-pressing of quenched samples at room temperature. Cold-pressed pellets were then annealed at 300°C in vacuum, and the thermoelectric properties and microstructure were traced through the course of the heat treatment. For the heavily deformed samples, the Seebeck coefficient rapidly increased at the very early stage of annealing and did not change as the annealing time increased, due to recrystallization of a new δ-phase which equilibrated at the annealing temperature of 300°C (δ300-phase). At the initial stage of annealing (recovery stage), the electrical resistivity sharply increased, probably due to the interaction of antistructural defects with vacancies produced during the cold-pressing treatment. However, for the lightly deformed samples, recrystallization occurred only at some portion of the grain boundaries, and the newly generated δ300-phase slowly replaced the original, as-solidified δingot-phase.

Electrical/thermoelectric characterization of electrodeposited Bi x Sb2−x Te3 thin films

BixSb2−xTe3 films were electrodeposited potentiostatically from acidic nitric baths at room temperature by controlling the electrodeposition parameters (i.e., the applied potential). Nearly stoichiometric BixSb2−xTe3 thin films were obtained at applied potentials between −0.10 and −0.15 V versus the saturated calomel electrode (SCE). The electrical and thermoelectric properties of the as-deposited films were degraded at more negative deposition potentials; this might be attributed to the greater defect density formed. The post-annealing process in the reducing environment improved the electrical and thermoelectric properties, possibly because of a decrease in antistructure defects.

Quasi chemical and defect correlation models for intermetallic compounds with B2-structure: new applications

A generalized, quantitative, and predictive statistical-thermodynamic model is proposed employing a quasi-chemical argument for description of thermodynamic behavior and ordering phenomena in B2 ordered binary intermetallic materials. A modified procedure is given for the application of the Bethe-Guggenheim QC method which takes into account the presence of all possible defects in the structure, both vacancies and anti-structure atoms. Interactions between nearest-neighbor atoms result in correlations between their arrangements in the crystal lattice. The QC method which can be regarded as the simplest form of the cluster variation method takes these correlations into consideration by describing the formation of point defect pairs and assuming random distribution of these point defect pairs. The results are compared with those obtained by the defect correlation model, a simple Ising-type model which is, however, able to describe defect clusters formed by two, three or even more atoms or vacancies in non-frustrated crystal lattices like the B2 structure. Both modeling approaches were applied for description of thermodynamic activities and vacancy concentrations over composition range and temperature in non-stoichiometric B2 ordered intermetallic compounds with triple-defect mechanism (PdIn, NiGa, and CoGa), as well as with substitutional (anti-structure) defect mechanism (FeCo, NiZn, AgMg). The (hypothetical) critical temperatures of the order–disorder transformations were derived from the model calculations. Comparison with a wealth of experimental data provided in the literature confirms the viability of these simple models.

Radiation-induced defects in InP〈Sn〉 single crystals irradiated with 60Co gamma quanta

The process of formation of antistructural defects in tin-doped InP crystals exposed to irradiation with gamma quanta of dose 10–100 kGy has been investigated by the radioluminescence method. It has been found that an activation energy of level 0.26 eV is favorable for obtaining semi-insulating indium phosphide.

High temperature defect equilibrium in ZnS:Cu single crystals

High temperature investigations in ZnS:Cu crystals were performed under defined conditions. High temperature electrical conductivity and copper solubility data were obtained under different component vapour pressures and under different sample temperatures. The experimental data at sulphur vapour pressure can be explained by the inclusion of abnormal site occupation i.e. by antistructural disorder. Compensating association of copper with this antistructure defect may occur. Antistructure disorder disappears with increasing of zinc vapour pressure and with increasing role of holes in bipolar conductivity. The method for solving the system of quasichemical reactions without approximation was used to model high temperature defect equilibrium. This model contains antistructure disorder and copper solubility limitation.

Solute diffusion in the γ′ phase of Ni based alloys

We systematically investigate the diffusion mechanisms of 3d (Ti–Cu), 4d (Zr–Ag) and 5d (Hf–Au) transition metal solutes in γ′-Ni3Al phase using first-principles calculations. The results reveal that the diffusion of Ni-substituting solute is mainly controlled by the sublattice diffusion mechanism via Ni vacancies and the diffusion of Al-substituting solute is mostly governed by the formation of the anti-structure defects on the Ni sublattice with negligible contribution of the anti-structure bridge mechanism. The elements which occupy both the Al and Ni sites show a diffusion behavior similar to that of the Ni-substituting solutes. Our calculations show that larger atoms can move much faster than smaller atoms, which disprove the traditional view that larger atoms move slower than smaller atoms.

Galvanomagnetic effects in A2VB3VI

Magnetoresistivity of A2VB3VI-based compounds has been investigated (H∼0÷89 kE, T=0,5÷4,2 K). Oscillation of magnetoresistivity, Shubnikov de Gaas oscillation has been observed at high magnetic fields (H>30 kE). The charge carrier concentration and area of extreme cross section of Fermi surface by plane, perpendicular to magnetic field have been evaluated from oscillation period.A52B63-based compounds are used as high effective thermoelectric transformers [1]. Recently, the interest to these compounds increases due to the perspectivities of widening of working temperature range and increase of thermoelectric efficiency of A52B63 compounds, doped by different impurities [2-6]. Therefore the investigation of fundamental characteristics of these compounds is not only extended our representation on band structure, also has a practical meaning.In the present work the results of investigations of galvanomagnetic effects in layered A52B63 compounds which have rhombohedral structure and crystallize in sp.gr. D3d (R÷m) [1], are given. The layers in A52B63 compounds consist of five monoatomic hexagonal grids alternating in sequence in B(1)-A-B(2)-A-B(1). Atom B(2) has 6 nearest atoms B(1). The bond between B(1)-A-B(2)-A-B(1) layers-quintets is of weak Van-der-Vaals type, but in layers of B(1)-A and A-B(2) bonds have covalent character with small fraction of ionic bond.Single crystals under investigation have been were grown by Bridgman method from components with stoichiometric relationship. It is known, that by synthesis of A52B63 compounds from the melt of stoichiometric structure are characterized by presence of a significant amount of own points defects conditioned by transition of A atoms into the position of B atoms. These antistructural defects are the acceptors. Concentration of holes is p∼1019cm-3. Investigations have been carried out in temperature range 0,5÷300K and magnetic field up to 8 Tl. At galvanomagnetic investigations the sample is placed in the centre of superconductive solenoid. Measurements are carried out by selective method under the alternating current by 20 Hz frequency. The current magnitude does not exceed 1MA. The current is directed along the layer plane, magnetic field is perpendicular to layer plane.

Electrophysical parameters of c-oriented Bi2Te3 films with a low concentration of antistructural defects

Epitaxial c-oriented Bi2Te3 films 1.2 μm in thickness are grown by the hot wall method for a low supersaturation of the vapor phase over the surface of mica substrates. The hexagonal unit cell parameters a = 4.386 A and c = 30.452 A of the grown films almost coincide with the corresponding parameters of stoichiometric bulk Bi2Te3 crystals. At T = 100 K, the Hall concentration of electrons in the films is on the order of 8 × 1018 cm−3, while the highest values of the thermoelectric coefficient (α ≈ 280 μV K−1) are observed at temperatures on the order of 260 K. Under impurity conduction conditions, conductivity σ of the films increases upon cooling in inverse proportion to the squared temperature. In the temperature range 100–200 K, thermoelectric power parameter α2σ of Bi2Te3 films has values of 80–90 μW cm−1 K−2.