Te Solid Solutions Research Articles

Aqueous chemical synthesis of nanoscale Bi2(Te,Se)3 and (Bi,Sb)2Te3 thermoelectric compounds

We introduce a simple aqueous chemical route for the synthesis of nanoscale Bi2Te2.7Se0.3 and Bi0.5Sb1.5Te3 solid solution thermoelectric compounds in this article. The method adapted is based on the reaction between BiCl3, Te and Se/Sb in an alkaline condition at 80 °C and under the normal atmospheric pressure without surfactant agent. The microstructures of the synthesized products are characterized by XRD and SEM. The result shows that the crystals are of high purity. This one-step, easy to control synthetic technique is utilized at low temperature and under normal atmospheric pressure, which opens up a prospect of its application in industry.

Structural and magnetic properties of Cr1−x V x Te (x = 0−0.4) solid solutions

Cr1−x V x Te solid solutions with a hexagonal structure (NiAs type) have been obtained in the composition range x = 0−0.4 by direct melting of elemental mixtures, followed by annealing and quenching. The 80-K magnetic moment is found to decrease from 2.4μB in CrTe to 1.52μB in Cr0.6V0.4Te. The Curie temperature varies from 342 K to 321 K, respectively.

Mechanochemical stability of Ge1 − x − y Sn y Te x glasses

The mechanochemical stability of glasses in the Ge1 − x − y Sn y Te x system is investigated. It is found that tin in Ge1 − x − y Sn y Te x vitreous alloys forms a system of sp 3 chemical bonds and that Ge1 − x Sn x Te solid solutions are formed in crystalline alloys. The dispersion of glasses at room temperature in air is accompanied by the precipitation of the SnO2 amorphous phase.

Atomic structure of Cd1 − x Zn x Te solid solution single crystals and structural prerequisites of their ferroelectricity

Precision X-ray structural investigation of Cd{sub 1-x}Zn{sub x}Te single crystals (x = 0.04, 0.10, 0.21, 0.30, 0.40) is performed at temperatures below and above the ferroelectric phase transition. The regularities associated with the increase in the concentration of Zn atoms in solid solutions are revealed. It is established that the unit cell parameter of the crystals varies according to the Vegard law. The thermal parameters of Te and Zn atoms are strongly overestimated within the model of a sphalerite-type average structure. It is found that the positions of the Zn cations are split and the anion sublattice is disordered in such a way that the Te anions are predominantly displaced along the threefold axes. The Zn atoms can serve as off-center impurities. This phenomenon offers strong possibilities for manifesting the ferroelectric properties in the solid solutions under investigation.

First-principles investigation of wide-gap quaternary alloys Zn 1− xMg xS yTe 1− y

We investigate the structural and electronic properties of (Zn, Mg) (S, Te) solid solutions using the full potential-linearized augmented plane wave method within density functional theory. We use the generalized gradient approximation that is based on exchange–correlation energy optimization for calculating the total energy. Moreover, the Engel–Vosko GGA formalism is applied so as to optimize the corresponding potential for band gap calculations. We study the effect of composition on lattice constant, bulk modulus and band gap for pseudobinary as well as for quaternary alloys which showed nonlinear dependence on the composition. The bowing of the fundamental gap versus composition predicted by our calculations is in very good agreement with experiments available for pseudobinary alloys. In addition, the energy band gap of zinc-blende Zn 1− x Mg x S y Te 1− y quaternary alloys lattice matched to GaAs substrate is investigated. It should be noted that the present work is the first theoretical study of the quaternary alloys of interest.

Chemical etching of CdxHg1-x Te single crystals in bromine-releasing aqueous H2O2-HBr-solvent solutions

The nature and mechanism of dissolution of single crystals of a Cd0.21Hg0.79Te solid solution in H2O2-HBr-solvent bromine-releasing aqueous solutions were determined, with water, ethylene glycol, and tartaric, citric, and lactic acids used as solvents. Projections of the surfaces of equal etching rates were constructed and the concentration limits were found for solutions that can be used for chemical-dynamical polishing of the surface of Cd0.21Hg0.79Te single crystals.

Temperature dependence of the specific heat for the CdxHg1−x Te solid solutions

Temperature dependence of the specific heat for the CdxHg1−x Te solid solutions

Preparation and Electrical Properties of CdxZn1−x Te Crystals

Single-crystal ingots of CdxZn1−x Te solid solutions are grown by the sublimation method. Samples with x = 0.95, 0.90, and 0.85 taken from the end portions of the ingots are chemically homogeneous and have p-type conductivity with a 300-K hole concentration below 1012 cm−3. Temperature-dependent electrical conductivity measurements are used to evaluate the ionization energies of electrically active centers.

The crystallographic structure of thin Mn-rich ZnMnTe layers grown by molecular beam epitaxy

Crystal structure of Mn-rich ZnMnTe/MnTe/Al 2O 3 heterostructures grown by molecular beam epitaxy (MBE) was investigated by X-ray diffraction. Zn content in the layers was tuned by Zn-effusion-cell temperature ( T Zn). Three phases occur simultaneously in the layers: hexagonal NiAs-type ZnMnTe (α-phase), cubic zinc blende ZnMnTe (β-phase) and, hypothetically, metastable, hexagonal wurtzite-type MnTe (γ-phase). The existence of α-Zn x Mn 1− x Te solid solution was proved and it was found that the c-lattice parameter of α-Zn x Mn 1− x Te increases with increasing x (in the case of β-Zn x Mn 1− x Te this dependence is opposite— a-lattice parameter decreases with increasing x). The relative contribution of the crystallographic phases in studied layers depends on the Zn content in the flux during the growth process: for the smallest Zn content, the α-phase dominates, while with the Zn increasing, the volume fractions of “γ-MnTe” and β-ZnMnTe phases increase. In the sample grown with the highest Zn content in the flux, the “γ-MnTe” phase is dominant. Finally, we compared our experimental results with theoretical considerations concerning possibilities of existence of the phases described above.

Determination of Hg activity in Hg0.8Cd0.2Te liquid and solid solutions by a quasi-closed-space method

A quasi-closed-space method is proposed for accurately measuring the vapor pressure of a volatile component over solid compounds (solutions) and melts containing this component. The method is used to determine the equilibrium Hg vapor pressure pHg over the Hg0.8Cd0.2Te solid solution between 623 and 1268 K within the homogeneity range of HgCdTe and at its boundaries. The results indicate a jump in pHg and a break in its temperature dependence at about 920 K, corresponding to the onset of melting. Above 623 K, the total equilibrium excess of Te in solid homogeneous Hg0.8Cd0.2Te is close to the concentration of charged Hg vacancies, as determined by Hall effect measurements.

Resonance scattering on In impurity in Pb 0.4Sn 0.6Te solid solutions

The Hall coefficient and resistivity were measured on a series of samples of InTe in Pb 0.4Sn 0.6Te solid solutions with varying indium content from 0 to 5 molar% . All samples show a p-type conductivity with the concentration of holes ∼10 19 cm −3 at 77 K . A considerable decrease of mobility calculated from the measurements was observed in the samples with high content of In. The contribution to the mobility, directly related to the scattering of holes into In atoms, was determined, and the scattering crosssection was estimated. We observed a drastic increase in the scattering crosssection with the rise of In content, which can be explained by the resonance scattering of holes into the band of quasi-local states of In. This result can also be explained with the use of the Breit–Wigner formula. The location of the In states in the valence band was also calculated using the Kane model.

Optical and magnetooptical study of CdTe crystals doped with rare earth ions

Exciton reflectance, magnetooptical Faraday effect and magnetic susceptibility of CdTe single crystals doped with Eu, Gd, Dy rare earth elements and Cd 1− x Dy x Te solid solutions have been studied. The largest enhancement of the Faraday rotation near the fundamental absorption edge has been found for case of dysprosium. At liquid helium temperature the Verdet constant of CdTe:Dy with dopant concentration about 10 20 cm −3 is two order larger than the values for pure CdTe. Negative sign of the Faraday rotation at room temperature and the temperature dependence of magnetic susceptibility suggest of paramagnetic behavior for this material. The features in spectral, concentration, temperature and magnetic field dependence of the Faraday effect have been revealed which give evidence for strong spin exchange interaction between f electrons of rare earth ions and s, p band carriers of CdTe:Dy and Cd 1− x Dy x Te crystals. In contrast, there are no experimental evidences for a such kind of exchange interaction in CdTe doped with Eu and Gd.

Observation of Bose condensation in (Pb0.4Sn0.6)0.86In0.14Te semiconductor solid solutions using Mössbauer spectroscopy

73As(73Ge) Mossbauer emission spectroscopy is used to ascertain that the transition of the (Pb0.4Sn0.6)0.86In0.14Te solid solution to a superconducting state is accompanied by a change in electronic density at the cation sites, and spatial inhomogeneities in the Bose condensate of Cooper pairs are revealed.

Specific heat, magnetic susceptibility and resistivity of In-doped Sn0.8Pb0.2Te

We report experimental results on In-doped Sn0.8Pb0.2Te solid solutions which are semiconductors with superconducting properties. We carried out simultaneous magnetic susceptibility and resistivity (four-point) measurements down to 1.5 K, as well as specific heat below 4.2 K, on poly-crystalline samples. All measurements indicate same critical temperature region, above which the specific heat exhibits a T3 behavior, with θD∼85 K consistent with that of the constituent elements. Application of a magnetic field (∼1 kG) suppresses the specific heat anomaly from the temperature range down to 2 K. The results suggest that this compound undergoes a bulk superconducting transition.

Numerical study for liquid phase epitaxy of Cd XHg 1− XTe solid solution

The paper presents a numerical study of natural convection in the liquid phase epitaxy of Cd X Hg 1− X Te solid solutions. The simulation is carried out in frame of 2D time-dependent model accounts for solutal convection in the Boussinesq approximation, the phase equilibrium and mass conservation at the liquid/solid interface. The effect of convective mass transfer on the growth dynamics of epitaxial layers, their composition, surface shape and composition uniformity along the growth direction and across the layer area have been studied over a wide range of experimental conditions.

Modification of the electrical and photoelectric properties of Mg0.15Cd0.85Te solid solutions as a result of pulsed laser irradiation within the transparency range

Changes in the equilibrium conductivity and photoconductivity of Mg0.15Cd0.85Te solid solutions exposed to pulsed laser radiation at a frequency from the transparency range of the crystal are studied as a function of the laser fluence. An increase in the photoconductivity and a shift of the photoconductivity long-wavelength limit to higher energies are found. A change in the electrical properties of the crystals is attributed to an increase in the concentration of donors with ionization energies E1=0.015 eV and E2=0.035 eV in the surface region. Possible causes and mechanisms of the changes in the photoelectric properties of the II-VI crystals exposed to laser radiation are analyzed.

Isothermal phase relations in the Au-Sb-Te system at 350 C

Isothermal phase relations in the Au-Sb-Te system have been investigated at 350°C by the reactions of pure elements of Au, Sb and Te in evacuated sealed glass tubes. Microprobe techniques were employed to determine the composition of each phase of the products. Most efforts were concentrated on the pseudo-binary join between AuSb2, aurostibite and AuTe2, calaverite and the phase relations between these phases and phases in the Sb and Te binary system. Two ternary phases whose compositions are Au1.9(Te2.645b0.46)3.1 and AuSbTe(phase A) were found to exist stably at 350 °C. The XRD pattern of the former phase is almost similar to that of montbrayite reported by BACHECHI (1972), but the composition of the former phase does not agree well with that, and the latter phase does not seem to have been reported as a distinct phase. Montbrayite shows some little solid solution field and has non-stoichiometric compositions. The composition of montbrayite in the present study is not located on the (Au,Sb)2Te3 stoichiometric line, but near the Au2(Te,Sb)3 line. Calaverite, AuTe2 dissolved AuSb2 components up to 11.8 mole per cent and aurostibite, AuSb2 dissolve less than 1 mole per cent AuTe2 component. The phase relations in the system were characterized by the tie line of tellerantimony, Sb2Te3 and gold, Au in the central portion of the diagram, by which independent two ternary systems were introduced, that is, the Au-Sb-Sb2Te3 and the Au-Sb2Te3-Te systems. As a result, right side phases in Figure 3, aurostibite(AuSb2), antimony(Sb) and δ phase ((Sb,Te) solid solutions,ss) in the former system do not coexist with left side phases, calaverite(AuTe2 ss), montbrayite, and tellurium(Te) in the latter system.

Studies on some structural and optical properties of Zn xCd 1− xTe thin films

Five Zn x Cd 1− x Te solid solutions with x=0.1, 0.3, 0.5, 0.7 and 0.9 at.% were synthesized by fusing stoichiometric amounts of Zn, Cd and Te constituents in silica tubes. Each composition was used in the preparation of a group of thin films with different thicknesses. Structural investigation of prepared films indicates that they have polycrystalline structure of four predominant diffraction peaks corresponding to (1 1 1), (2 2 0), (3 1 1) and (3 3 1) reflecting planes. The refractive index, n, and the extinction coefficient, k, of Zn x Cd 1− x Te thin films of different compositions were determined in the spectral range, 500–2000 nm. It was found that at a certain wavelength these constants depend on the film’s structure, i.e. they are decreased with increasing the atomic percentage x. Also, plots of ( αhν) 2 versus hν yield straight lines corresponding to direct allowed transitions. However, the band gap showed a non-linear variation with the value of x. The refractive index data were analyzed by using the Wemple–DiDomenico single oscillator fit. The effective masses of the carriers and the band gap bowing parameters of Zn x Cd 1− x Te thin films were estimated.

Density of localized states in (Pb0.78Sn0.22)0.95In0.05Te solid solutions

The hopping conductivity and the Seebeck coefficient have been measured in Pb0.78Sn0.22Te with 5 at. % In and supplementary donor doping with Cl. The experimental data obtained are compared with similar results for supplementary acceptor doping with Tl. At temperatures of 150 K and higher, the thermoelectric power changes its sign from positive to negative on the introduction in sufficient amounts of either donors or acceptors. An analysis of the dependence of the thermoelectric power on the content of supplementary donors and acceptors yields the density of localized indium states as a function of energy. The function is essentially nonmonotonic, exhibiting both a density-of-states peak and a minimum between this peak and the conduction band.

Electrical properties of metal–insulator–semiconductor transistor structures based on Mn xHg 1− xTe films

The main properties of metal–insulator–semiconductor transistors with an induced channel were determined. These transistors were made of p-type Mn x Hg 1− x Te solid solutions ( x≈0.3) operating in the accumulation regime.