Annealing Of Single Crystals Research Articles

Synthesis and annealing effect of structural, morphology, optical, and magnetic properties of tin telluride (SnTe)

This study explored the structural, vibrational, morphological, optical, and magnetic characteristics of both as-grown and annealed single crystals of tin telluride (SnTe), employing diverse analytical techniques. X-ray powder diffraction (XRD) analysis shows the cubic lattice structure of SnTe with consistent lattice parameters across different temperatures, along with the phase transition phenomenon. Fourier Transform Infrared Spectroscopy (FTIR) elucidates temperature-induced shifts in vibrational modes, indicating sensitivity to thermal stimuli. Scanning electron microscopy (SEM) reveals layer-by-layer growth patterns and temperature-dependent variations in crystal morphology. Energy-dispersive X-ray analysis (EDAX) confirms the synthesized crystals' high purity and slight tellurium-rich composition. Optical band gap measurements demonstrate an increase in band gap upon annealing, attributed to valence band convergence. Field-dependent magnetization (M − H) curves exhibit ferromagnetic properties at ambient temperature, which escalate with increasing annealing temperature. Electron Paramagnetic Resonance (EPR) spectra reveal spin mobility and exchange coupling, with variations in the g-factor suggesting the presence of additional spin entropy. These observations offer significant insights into the complex properties of SnTe, which are crucial for its potential applications across various technological fields.

Annealing Effect on the Composition and Electrophysical Properties of N-Type Silicon Surface

During low-temperature annealing, the segregation of the alloying element leads to a strong enrichment of the surface layer, causing a rearrangement of the surface electron structure. This change in the electron structure is manifested in the characteristic energy loss spectra. Annealing of single crystals at 400–500 K leads to an increase in the density of surface electron states. As shown by the calculations of the surface potential using experimental data on the temperature dependence of the surface concentration, dopant segregation causes a linear increase in the surface potential.

Thermoelectric properties of Bi2Sr2Co2Oy thin films and single crystals

Bi2Sr2Co2O9 exhibits a misfit-layered structure with good thermoelectric properties. We have investigated the thermoelectric properties of Bi2Sr2Co2Oy in both thin-film and single-crystal forms. Among thin films grown at different temperatures, we find that both the in-plane thermoelectric power (Sab) and electrical resistivity (ρab) vary in an opposite trend, i.e., Sab is high when ρab is small. This results in large power factor (Sab2/ρab~5.5μW/K2cm for the film grown at 700°C), comparable to that for whiskers. For single crystals, the electrical resistivity shows metallic behavior in a large temperature range, but has higher magnitude than that of films grown at 675°C and 700°C. The annealing of single crystals under Ar atmosphere leads to even higher resistivity while Sab is improved. We discuss the thermoelectric performance of this material considering both oxygen concentration and phase purity.

Atomic scale imaging of structural changes in solid electrolyte lanthanum lithium niobate upon annealing

La(1-x)/3LixNbO3 (LLNbO) is a promising electrolyte material for solid-state lithium-ion batteries because it is stable in contact with Li metal and contains a high concentration of intrinsic Li-ion vacancies. One strategy for improving its ionic conductivity and making it more competitive with other solid-state Li-ion electrolytes is to disorder the Li-ion vacancies by appropriate post-synthesis heat treatment, e.g., annealing. In this study, we examine the effects of annealing on single crystals of LLNbO with Li contents x = 0.07 and 0.13 based on simultaneous atomic resolution high angle annular dark field and annular bright field imaging methods using state-of-the-art aberration corrected scanning transmission electron microscopes. It is found that La modulation within A1 layers of the cation-deficient layered perovskite structure becomes more diffuse after annealing. In addition, some La atoms move to A-site positions and O4 window positions in the nominally vacant A2 layer, while O atom columns in this layer become rumpled in the [001]p direction, indicating that the NbO6 octahedra are more heavily distorted after annealing. The observed crystal structure differences between as-prepared and annealed single crystals explain the drop in Li-ion conductivities of LLNbO single crystals after heat treatment.

Bulk properties of the UCoGe Kondo-like system

We report on extensive experimental investigations of a single crystal of the orthorhombic uranium compound UCoGe. Bulk measurements on as-grown and annealed single crystals, recording magnetization, magnetic susceptibility, electrical resistivity, magnetoresistivity, thermopower, thermal conductivity and heat capacity data do not reproduce the previously reported coexistence of ferromagnetism with superconductivity. The latter phenomenon was only observed for the annealed sample at T SC = 0.65 K. New observations show a crossover at around 13 K, visible in thermal and transport measurements as well as the coherent state around 50 K, signaled by a wide knee in ρ(T). Above this temperature, UCoGe exhibits a single-ion Kondo-like effect. The magnetoresistivity of the annealed single crystal increases negatively down to 4.2 K, reaching as a large value about −27% at a field of 8 T. The latter may be interpreted in terms of fairly strong magnetic fluctuations existing in UCoGe at low temperatures.

Dielectric, magnetic, and lattice dynamics properties of Y-type hexaferrite Ba0.5Sr1.5Zn2Fe12O22: Comparison of ceramics and single crystals

We prepared multiferroic Y-type hexaferrite Ba0.5Sr1.5Zn2Fe12O22 ceramics and compared their magnetic and dielectric properties with single crystal. Magnetic susceptibility and microwave resonance measurement revealed magnetic phase transition at TC=312 K, similar as in single crystal. Ferroelectric (FE) phase can be induced by external magnetic field in all investigated samples and the phase diagram in ceramics qualitatively resembles that of the single crystal. The range of magnetic fields, where the FE phase is induced, broadens after annealing of single crystal. Ceramics quenched after sintering exhibit several orders of magnitude lower conductivity than the single crystal. Heavily damped magnetic resonance was discovered in terahertz spectra at 10 K and its frequency softens below 5 GHz near TC. Number and symmetry of observed infrared (IR) and Raman active phonons correspond to paraelectric phase with D3d5 hexagonal structure. No evidence for a structural phase transition was found in the IR and Raman spectra on cooling (in zero magnetic field) or in the room-temperature IR spectra with external static magnetic field up to 0.3 T.

Optical and electrical properties of β-FeSi 2 single crystals

β-Iron disilicide (FeSi 2) single crystals were grown by the chemical vapor transport (CVT) with iodine (I 2) as a transport agent. The optical and electrical properties of the crystals were then studied. Raman spectrum shows a set of strong A g-mode peaks and photoluminescence (PL) spectra show a very broad emission band. In order to study the effect of annealing on the electrical properties, β-FeSi 2 single crystals were annealed in the range of 1073–1213 K for 48 h. The electrical properties of as-grown and annealed crystals were then evaluated by measuring their Hall effects in the temperature range of 10–300 K. The results show that both of the as-grown and annealed single crystals are of the n-type conductivity. The dependences of the temperature indicate that carrier concentration decreases and Hall mobility increases with the increase of measuring temperature. When the annealing temperature reaches above 1223 K, these changes tend to saturation. Furthermore, the donor ionization energies were estimated and the scattering mechanisms of carrier were discussed.

Influence of reducing annealing on the luminescent properties of Li 2B 4O 7:Cu single crystals

Li 2B 4O 7:Cu single-crystal annealing in the reducing environment results in a sharp drop of intensity of thermoluminescence (TSL) and X-ray luminescence (XL) peaks. It was suggested that during annealing in the reducing environment, an oxygen vacancy is produced in the LTB structure at the bridging oxygen atom site. Oxygen vacancy charge compensation takes place at the expense of reduction of the doping Cu + ion to the Cu 0 state. In this case the A 0-type thermoluminescence center formation mechanism due to irradiation becomes impossible.

Oxygen diffusion in orthopyroxene TG study

Oxygen partial pressure is supposed, by analogy with olivines, to influence the kinetics of the Fe-Mg exchange reaction in orthopyroxene. It has been demonstrated for olivines that the Fe−Mg interdiffusion coefficient is dependent on P(O2), according to D Fe−Mg ∝ P(O2)∼1/6 [1−3]. By means of thermogravimetric analyses performed at different P(O2) on orthopyroxene grains from a volcanic rock it was possible to detect a certain degree of non-stoichiometry which is function of P(O2).Oxygen moves into or out of the orthopyroxene lattice in response to a compositional gradient. Therefore, in orthopyroxene too, the Fe/Mg interdiffusion and hence the kinetics of the Fe−Mg intracrystalline exchange should be affected by P(O2). The oxygen chemical diffusion coefficients at P(O2)∼5⋅10−19atm were calculated at ∼400, 500 and 600°C. It was also verified on the orthopyroxene from the TPK-30F granulite that, at the operating conditions normally used for single-crystal annealing experiments, oxygen quickly responds to a chemical potential gradient in order to maintain the system in equilibrium conditions.

Thermal hysteresis in magnetization of single crystal URu 2Si 2

We present low field magnetization results of URu 2Si 2 single crystals, measured after zero-field cooling and field cooling with fields applied along the a- and c-axes. To investigate heat treatment effects on magnetization, we prepared both unannealed and annealed single crystals. In all the samples we studied, we found thermal hysteresis in the low field magnetization, and temperatures where the hysteresis starts differ for the a- and c-axes samples. However it tends to disappear with increasing fields. There are also subtle, but measurable, effects of annealing on the low field magnetization in all the samples. We compare our results with a previous similar study of polycrystalline URu 2Si 2, and heat treatment effects found in neutron diffraction.

Electrical conduction in CuWO4 crystals

The d.c. electrical conductivity and thermoelectric power of CuWO4 have been measured in the temperature range 300 to 700 K on unannealed and annealed single crystals and on polycrystalline pellets. It has been found that CuWO4 is an n-type semiconductor. Relevant conduction mechanisms appropriate to the regions below and above 455 K are discussed on the basis of the experimental data on activation energy, mobility and carrier concentration.

Evolution of crystallization structure during deep deformation and annealing of single crystals of austenitic carbon steel

The distribution of alloying elements, impurities, and secondary phases in axial and interaxial regions was studied for single crystals of the austenitic carbon steel, 04Kh17N14M3BG2, with the classical cross-shaped dendritic structure. It was shown that the interaxial regions are enriched with chromium, molybdenum, and carbon and contain precipitates of Cr23C6 and Mo2C. The chemical and phase inhomogeneities, connected with dendritic crystallization, are stable with respect to the effect of deep deformation and annealing, and in the finished product evolve into bands with a different content of impurities and second phase particles.

High‐Temperature Equilibrium Carrier Density of Arsenic‐Doped Silicon

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First investigation of the atomic structure of (112) and ( [formula omitted]) CuInSe 2 surfaces

The atomic structure of (112) and ( 112 ) surfaces of CuInSe 2 has been studied with low energy electron diffraction. The surfaces were prepared by sputtering and annealing of single crystals in ultrahigh vacuum. The symmetry and size of the resulting unit cells on both surfaces were found to be incompatible with the substitutional ordering of the metal sublattices. Non-stoichiometry at the surface and randomization of the metal sublattices by ion sputtering are invoked to explain this result.

Room-temperature deformation mechanisms and the defect structure of tungsten carbide

Defects in undeformed, annealed single crystals and in deformed single crystals of WC are characterized by transmission electron microscopy. Deformation is induced by indentation with a microhardness tester. High densities of stacking faults with atomic displacement vectors R = 1 6 〈11 2 ̄ 3〉 are found lying on {11̄00} planes near the indentations. Stacking faults with R = 1 6 〈11 2 ̄ 3〉 and undissociated dislocations with b = 〈0001〉, 1 3 〈11 2 ̄ 0〉, and 1 3 〈11 2 ̄ 3〉 are observed at distances greater than 2μm from an indentation. The Burgers vectors of the partial dislocations bounding one fault are found to be identical b p = 1 6 [11 2 ̄ 3 ̄ ] , resulting in a total Burgers vector for the extended dislocation b = 1 3 [11 2 ̄ 3 ̄ ] . (Stacking fault energy = 55 mJ/m 2). Stacking faults with R = 1 6 〈11 2 ̄ 3〉 are described in terms of the crystal structure of WC, illustrating several points: the coordination of carbon atoms by tungsten atoms is preserved at the fault, the number of bonds per atom which are broken during slip may be minimized, and the 1 6 〈11 2 ̄ 3〉 type of partial Burgers vector may be combined to form several types of total Burgers vector.

ESR studies of diamond powders

The ESR spectrum of two defect centres were observed in finely ground diamond powders (0.5 to 30 μm size). The one centre has been seen before in irradiated and annealed single crystals of natural diamonds (the O 1 centre) while the second one has only been seen in synthetic diamonds grown from a nickel-iron melt and is only observable below 250 K. From the study of the variation of the intensity of these lines with size of particles it could be concluded that the O 1 centre lies just beneath the surface of these particles and the S centre at least 0.5 μm below the surface.

Oxidation of nickel studied by UV and X-ray photoelectron spectroscopy

The nature of argon-ion bombarded nickel surfaces (polycrystalline, and (111), (110) and (100) single crystals) and their subsequent interaction with oxygen at ordinary temperatures have been studied using X-ray and UV photoelectron spectroscopy, including angular variation measurements and the determination of work function changes, in combination in the same apparatus. Variations between the HeI spectra of the four clean substrates were taken to confirm the presence of substantial order within the depth sampled by UPS. The four surfaces exhibited similar but not identical behaviour during oxidation, resembling that reported by other workers from studies of both annealed single crystals and evaporated polycrystalline films. The initial process was deduced to be essentially dissociative chemisorption: no evidence supporting a previous suggestion of associative adsorption at low coverages was found. Oxygen commenced to penetrate below the surface of all samples before oxygen equivalent to a monolayer had been taken up (~10 L exposure) and further substantial uptake followed resulting in the formation of a stable film (~18 Å) of nickel oxide by ~100 L exposure. This oxide layer was not stoichiometric nickel(II) oxide: it was characterized by the presence of two distinct O 1s signals, the relative intensities of which depended on the crystallographic nature of the surface. It is tentatively suggested that the oxygen signal with the higher BE be associated with Ni III. Comparison of the X-ray and UV spectra suggests that the oxide film is very non-uniform in thickness, some Ni metal remaining very close to the surface.

Morphological effects of annealing in linear polyethylene

Abstract Observations are presented of the microstructural changes occurring on annealing in a bulk, unfractionated, Marlex 6002 linear polyethylene. The material was isothermally crystallized at 110°C, and annealed at 118°C, 123°C, and 126°C, for 3 and 72 hours. The microstructure was studied by electron microscopy of fracture surface replicas and acid-etched lamellar fragments. A direct correspondence between the annealing process observed here and observations in the annealing of single crystals was noted. Electron fractographs showed the development of thickened ridges along lamellae faces with perforations at the ridge boundaries. Later stages showed multiple ridge formation. Etched fragments showed essentially the same results. Histograms of the etched fragment thicknesses showed the development of a bimodal distribution apparently relating to values for unaffected lamellar interiors and for ridges.

Determination of the molecular weight spread of narrow peaks in the gel‐permeation chromatograms of nitric acid‐degraded polyethylene

AbstractA method for the determination of the molecular weight spread in the narrow peaks in the GPC chromatograms of nitric acid‐degraded polyethylene is presented. It is found that polar endgroups added to the polymer chains during scission cause the peaks to be broader than those of paraffins with the same molecular weight spread. After allowing for this extra instrumental broadening, estimates are made of the molecular weight spread for unannealed and annealed single crystals of polyethylene and bulk polyethylene as a function of degradation time. It is proposed that after long degradation times the molecular weight spread is a measure of fluctuations in the original crystalline lamellar thickness.

GPC analysis of degraded annealed single crystals

AbstractAnnealed polyethylene single crystals have been degraded with fuming nitric acid, and the molecular weight distribution of the fragments determined by using a gel‐permeation chromatograph. Peaks due to chain folding were observed in these distributions as for unannealed single crystals. The peaks moved to lower molecular weight with increasing degradation time. Comparison of the lowest molecular weight peak length after a given degradation time with the low‐angle x‐ray periodicity before degradation gave information about a disordered surface layer. The thickness of this layer at early states of degradation was dependent solely on annealing temperature, though changes in the layer must have occurred with annealing time, since there was an increase in reaction rate with annealing time. At higher degradation states, the thickness of the layer was dependent solely on the original low‐angle periodicity. This has been related to the depth at which some folds are buried beneath the lamellar surfaces. The relevance of these observations to the structure of annealed single crystals is discussed.