Sb2Te3 Single Crystals Research Articles

Signatures of crossover between weak anti-localization to weak localization effect in Gd doped Sb2Te3 single crystal

Signatures of crossover between weak anti-localization to weak localization effect in Gd doped Sb2Te3 single crystal

Growth and Characterization of Pure and Sm-Doped Sb2Te3 Single Crystal

Growth and Characterization of Pure and Sm-Doped Sb2Te3 Single Crystal

Effect of Magnetic (Nd) Doping on Electrical and Magnetic Properties of Topological Sb2Te3 Single Crystal

Here, we report the growth and characterization of single crystals of NdxSb2-xTe3 (x = 0 and 0.1), by solid-state reaction route via self-flux method. The phase and layered growth are confirmed through X-ray diffraction and scanning electron microscopy respectively. A slight contraction in lattice parameters is seen after Nd doping. Also a minute shift in vibrational modes of recorded Raman spectra has been observed by doping of Nd in Sb2Te3. The magneto-resistance values under magnetic field of 5 Tesla for Sb2Te3 are 75% at 2.5 K and 60% at 20 K, but only 40% at 5 K for Nd0.1Sb1.9Te3. DC magnetic measurements exhibit expected diamagnetic and paramagnetic behaviors for pure and Nd doped crystals respectively. A cusp-like behavior is observed in magneto-conductivity of both pure and Nd doped crystals at low magnetic fields (< 1 Tesla) which is analyzed using Hikami-Larkin-Nagaoka (HLN) model. For Sb2Te3, the fitted parameters α are −1.02 and −0.58 and the phase coherence lengths Lφ are 50.8(6)nm and 34.9(8)nm at temperatures 2.5 and 20 K respectively. For Nd0.1Sb1.9Te3, α is −0.29 and Lφ is 27.2(1)nm at 5 K. The α values clearly show the presence of weak anti-localization effect in both pure and Nd doped samples. Also with Nd doping, the contribution of bulk states increases in addition to conducting surface states in overall conduction mechanism.

Anharmonicity of Lattice Vibrations in Bi2Se3 Single Crystals

The temperature dependences of the Raman-active frequencies $$E_{g}^{2}$$ , $$A_{{1g}}^{2}$$ in layered Bi2Se3 single crystals are studied. The contribution of the thermal expansion to a temperature variation in the frequencies is determined. The decay of the anisotropy of the elastic properties in layered Bi2Se3 single crystals due to strong spin–orbit coupling is shown. The Gruneisen-mode parameters for phonons $$E_{g}^{2}$$ and $$A_{{1g}}^{2}$$ are calculated. Systematic features in the dependences of vibrational frequencies on the atomic masses in layered Bi2Te3, Bi2Se3, and Sb2Te3 single crystals are determined.

Crystal growth and characterization of bulk Sb2Te3 topological insulator

The Sb2Te3 crystals are grown using the conventional self flux method via solid state reaction route, by melting constituent elements (Sb and Te) at high temperature (850 °C), followed by slow cooling (2 °C/h). As grown Sb2Te3 crystals are analysed for various physical properties by x-ray diffraction (XRD), Raman Spectroscopy, Scanning Electron Microscopy (SEM) coupled with Energy Dispersive x-ray Spectroscopy (EDAX) and electrical measurements under magnetic field (6 Tesla) down to low temperature (2.5 K). The XRD pattern revealed the growth of synthesized Sb2Te3 sample along (00l) plane, whereas the SEM along with EDAX measurements displayed the layered structure with near stoichiometric composition, without foreign contamination. The Raman scattering studies displayed known ( and ) vibrational modes for the studied Sb2Te3. The temperature dependent electrical resistivity measurements illustrated the metallic nature of the as grown Sb2Te3 single crystal. Further, the magneto—transport studies represented linear positive magneto-resistance (MR) reaching up to 80% at 2.5 K under an applied field of 6 Tesla. The weak anti localization (WAL) related low field (±2 Tesla) magneto-conductance at low temperatures (2.5 K and 20 K) has been analysed and discussed using the Hikami—Larkin—Nagaoka (HLN) model. Summarily, the short letter reports an easy and versatile method for crystal growth of bulk Sb2Te3 topological insulator (TI) and its brief physical property characterization.

Topological insulator Sb_2Te_3 as an optical media for the generation of ring-shaped beams

Hexagonal nanosheets of Sb2Te3 single crystals with uniform morphology are successfully synthesized through a solvothermal method. We experimentally demonstrate that topological insulator Sb2Te3 as an optical media can be used for the generation of ring-shaped beams based on a giant optical nonlinearity and the effect of graded-index plasma lens. Good propagation properties in free space are exhibited by the generated ring-shaped beam and the dark spot size of ring-shaped beams can be conveniently controlled by adjusting the power of the pump beam. We also find that it is more easily to generate a ring-shaped beam in the high concentration Sb2Te3 dispersion solution and the divergence angle of the ring-shaped beam increases as the concentration of dispersion solution increase.

Detailed Theoretical Investigation and Comparison of the Thermal Conductivities of n- and p-type Bi2Te3 Based Alloys

ABSTRACTIn this work we present a detailed theoretical investigation of the thermal conductivities of n-type 0.1 wt.% CuBr doped 85% Bi2Te3 - 15% Bi2Se3 and p-type 3 wt% Te doped 20% Bi2Te3 - %80 Sb2Te3 single crystals. The thermal conductivity contributions arising from carriers, electron-hole pairs and phonons are computed rigorously in the temperature range $300\,{\rm{K}}\, \le \,T\, \le \,500\,{\rm{K}}$. In agreement with available experimental measurements we theoretically find that the lowest total thermal conductivity is 3.15 W K−1 m−1 at 380 K for the n-type alloy and 1.145 W K−1 m−1 at 400 K for the p-type alloy. Stronger mass-defect scattering is found to be responsible for the lower thermal conductivity of the p-type alloy throughout the temperature range of the study.

Structure and magnetic properties of Cu-doped Bi2Te3 and Sb2Te3 single crystals

We report on the structure and the magnetic properties of Bi1.985Cu0.015Te3 and Sb1.988-Cu0.012Te3 single crystals prepared using the temperature gradient solidification method. The crystals structure was rhombohedral, and the lattice constants decreased with the addition of Cu. The hole carrier conduction was observed in Hall-effect and thermopower measurements. The carrier densities and thermopowers at 300 K were 1.538 × 1020 cm−3/218.5 µV/K and 1.132 × 1021 cm−3/36.8 µV/K for Bi1.985Cu0.015Te3, and Sb1.988Cu0.012Te3, respectively. We could observe a strong diamagnetism with weak ferromagnetic hysteresis, indicating a mixture of non-magnetic and ferromagnetic ordering between Cu-ions in Bi2Te3 and Sb2Te3.

Anomalous thermal expansion of Sb2Te3 topological insulator

We have investigated the temperature dependence of the linear thermal expansion along the hexagonal c axis (ΔL), in-plane resistivity (ρ), and specific heat (Cp) of the topological insulator Sb2Te3 single crystal. ΔL exhibits a clear anomaly in the temperature region 204–236 K. The coefficient of linear thermal expansion α decreases rapidly above 204 K, passes through a deep minimum at around 225 K, and then increases abruptly in the region 225–236 K. α is negative in the interval 221–228 K. The temperature dependence of both α and Cp can be described well by the Debye model from 2 to 290 K, excluding the region around the anomaly in α.

Thermoelectric properties of Bi2Te3, Sb2Te3 and Bi2Se3 single crystals with magnetic impurities

Temparature dependence of Seebeck coefficients S, electrical conductivity, heat conductivity k and dimensionless thermoelectric figure of merit ZT of p-Bi2Te3, Sb2Te3 and n-Bi2Se3-doped by Fe or Cr were carried out in the temperature interval 7<T<300K. At T=4.2K Shubnikov-de Haas and Hall effects have been measured. By increasing the Fe content, the hole concentration decreases in p-Bi2−xFexTe3, while the electron concentration increases in n-Bi2−xFexSe3. The decrease of the hole concentration was observed in p-Sb2−xCrxTe3 single crystals with Cr-doping. This demonstrates that Fe or Cr act as donors. The Seebeck coefficient increases in p-Bi2−xFexTe3 and Sb2−xCrxTe3 with increasing Fe or Cr content, while it decreases in n-Bi2−xFexSe3. Cr-doping increases dimensionless thermoelectric figure of merit ZT in Sb2Te3 at T>150K.

Temperature dependence of Raman-active optical phonons in Bi2Se3 and Sb2Te3

Inelastic light scattering spectra of Bi2Se3 and Sb2Te3 single crystals have been measured over the temperature range from 5 K to 300 K. The temperature dependence of dominant A1g2 phonons shows similar behavior in both materials. The temperature dependence of the peak position and linewidth is analyzed considering the anharmonic decay of optical phonons and the material thermal expansion. This work suggests that Raman spectroscopy can be used for thermometry in Bi2Se3- and Sb2Te3-based devices in a wide temperature range.

Giant Interlayer Magnetoresistances and Strong Anisotropy in p-type Sb2Te3 Single Crystals

Anisotropic interlayer magneto-transport properties have been studied over a broad range of temperatures and magnetic fields in p-type Sb2Te3 single crystals. Giant interlayer magnetoresistance (MR) of up to 400% was observed, which exhibits quadratic field dependences in low fields and becomes linear at high fields without any trend towards saturation. The interlayer MR displays strong anisotropy and is attributable to the anisotropy of the Fermi surface. The observed giant anisotropic interlayer MR could find applications in p-type Sb2Te3 based magneto-electronic devices.

Stacking fault in Bi2Te3 and Sb2Te3 single crystals

The structural characterizations of the Bi2Te3 and Sb2Te3 single crystals grown by the Zone melting method have been carried out by XRD and Chemical Etching process. The top free surface of as-grown Bi2Te3 and Sb2Te3 single crystal were observed under optical microscope. The particle size was calculated for a number of reflections using Scherrer’s formula by X-ray diffraction method. By the use of XRD data, the growth and deformation fault probability has been estimated for the grown single crystals. The presence of stacking fault in the lattice structure of the grown crystals was verified by the probability of growth and dislocation fault. Also new dislocation etchant has been developed by the successive trial–error method. Dislocation etching was achieved on (111) crystal plane examined using a saturated solution of citric acid and nitric acid as the etchant. The dislocation etchant has been found to give reproducible etch pits on the cleavage surface for an appropriate etching time 30s. The use of citric acid and nitric acid proved to be especially advantageous for the basal plane, producing etched pits suitable for dislocation etch pit counting.

Nernst-ettingshausen tensor in Sb2Te3 single crystal

On one Sb2Te3 single crystal, the temperature dependences of all three independent components of the Nernst-Ettingshausen tensor (Qikl) are measured in the temperature range of 85–450 K, all three components being negative. Alongside with the Nernst-Ettingshausen effect, the anisotropy of the Hall (Rikl) and Seebeck (Sij) coefficients and the conductivity (σii) is also investigated. The carried-out analysis of the experimental data on the Nernst-Ettingshausen and Seebeck effects indicates that there is the mixed scattering mechanism with the participation of acoustic phonons and impurity ions, the relative contributions of these mechanisms varying with temperature. In the relaxation-time-tensor approximation, the values of the effective scattering parameter (r) are determined. The obtained values point to the dominant scattering at acoustic phonons in the cleavage plane and to the substantial contribution of charged ions to the scattering along the trigonal axis c3. It is shown that it is possible to explain the major features of experimental data on the Nernst-Ettingshausen effect within the two-valence-band model with the participation of several groups of holes in the transport phenomena.

Deposition of antimony telluride thin film by ECALE

The process of Sb2Te3 thin film growth on the Pt substrate by electrochemical atomic layer epitaxy (ECALE) was studied. Cyclic voltammetric scanning was performed to analyze the electrochemical behavior of Te and Sb on the Pt substrate. Sb2Te3 film was formed using an automated flow deposition system by alternately depositing Te and Sb atomic layers for 400 circles. The deposited Sb2Te3 films were characterized by XRD, EDX, FTIR and FESEM observation. Sb2Te3 compound structure was confirmed by XRD pattern and agreed well with the results of EDX quantitative analysis and coulometric analysis. FESEM micrographs showed that the deposit was composed of fine nano particles with size of about 20 nm. FESEM image of the cross section showed that the deposited films were very smooth and dense with thickness of about 190 nm. The optical band gap of the deposited Sb2Te3 film was determined as 0.42 eV by FTIR spectroscopy, and it was blue shifted in comparison with that of the bulk Sb2Te3 single crystal due to its nanocrystalline microstructure.

Formation and Characterization of Sb2Te3 Nanofilms on Pt by Electrochemical Atomic Layer Epitaxy

A nanocrystalline Sb2Te3 VA-VIA group compound thin film was grown via the route of electrochemical atomic layer epitaxy (ECALE) in this work for the first time. The electrochemical behavior of Te and Sb on Pt, Te on Sb-covered Pt, and Sb on Te-covered Pt was studied by methods of cyclic voltammetry, anode potentiodynamic scanning, and coulometry. A steady deposition of the Sb2Te3 compound could be attained after negatively stepped adjusting of the UPD potentials of Sb and Te on Pt in each of the first 40 depositing cycles. The structure of the deposit was proven to be the Sb2Te3 compound by X-ray diffraction. The 2:3 stoichiometric ratio of Sb to Te was verified by EDX quantitative analysis, which is consistent with the result of coulometric analysis. A nanocystalline microstructure was observed for the Sb2Te3 deposits, and the average grain size is about 20 nm. Cross-sectional SEM observation shows an interface layer about 19 nm in thickness sandwiched between the Sb2Te3 nanocrystalline deposit and the Pt substrate surface. The optical band gap of the deposited Sb2Te3 film was determined as 0.42 eV by FTIR spectroscopy and it is blueshifted in comparison with that of the bulk Sb2Te3 single crystal because of its nanocrystalline microstructure.

Magnetic properties of Mn‐doped Bi2Te3 and Sb2Te3

AbstractWe have fabricated Mn‐doped Bi2Te3 and Sb2Te3 single crystals by the vertical gradient solidification method. The compositions and crystal structures of Bi2−xMnxTe3 and Sb2−xMnxTe3 were determined using Electron Probe Micro‐Analyzer (EPMA) and powder X‐ray diffraction (XRD) patterns, respectively. Both crystal structures were rhombohedral with smaller lattice constants because of the smaller atomic radius of Mn than those of Bi and Sb. Based on the magnetization measurements, Mn‐doped Bi2Te3 and Sb2Te3 compounds have ferromagnetic ordering at TC = 10 and 17 K, respectively. (© 2004 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Electrophysical properties and electronic structure of tin-doped antimony telluride

The effect of Sn atoms on the electrophysical properties and x-ray photoelectron spectra of Czochralski-grown Sb2Te3 single crystals is studied. The character of the temperature dependences of the kinetic coefficients is shown to depend noticeably on the structure of the valence band, which consists of two valence subbands. Estimates of the effective density-of-states masses of holes and of the gap between the valence-band extrema in Sb2Te3: Sn agree with the data available for the Sb2Te3 not doped with tin. X-ray photoelectron spectra of Sb2Te3: Sn single crystals do not exhibit noticeable core-level shifts and electron density redistribution in the valence band.

The Nernst-Ettingshausen, Seebeck, and Hall effects in Sb2Te3 single crystals

This paper reports on measurement of the temperature dependences of the following transport coefficients: electrical conductivity in the σ11 cleavage plane, the Seebeck coefficients S11 and S33 (axis 3 is along the trigonal crystal axis), the Hall coefficients R123 and R321, and the Nernst-Ettingshausen constant Q123; all measurements were made on high-quality Czochralski-grown Sb2Te3 single crystals. The results obtained are analyzed in terms of phenomenological theory. It is shown that the main features of the experimental data, including the anisotropy of the Hall and Seebeck effects, can be explained within a two-band model with notice-ably different anisotropy of the mobilities of holes of two types in the cleavage-plane and trigonal-axis directions. Estimates are made of the band-gap width (ɛg≅0.3 eV), as well as of the energy gap between the main and additional valence-band extrema (Δɛv∼0.1 eV).

Effects of excess Te on the thermoelectric properties of p-type 25% Bi2Te3-75% Sb2Te3 single crystal and hot-pressed sinter

Effects of excess Te on the thermoelectric properties of p-type 25% Bi2Te3-75% Sb2Te3 single crystal and hot-pressed sinter were characterized and understood with the micro-phase diagram near the stoichiometric composition obtained by measuring the equilibrium Seebeck coefficient. Thermoelectric properties of the 25% Bi2Te3-75% Sb2Te3 single crystal were varied with the amount of excess Te, as δ-phase of the single crystal becomes less Te-deficient with adding more excess Te. However, thermoelectric properties of the hot-pressed sinter were not varied with the amount of excess Te, because the composition of δ-phase is not changed with the amount of excess Te. While a maximum figure-of-merit of 2.39 × 10−3/K at 300 K was obtained for the 25% Bi2Te3-75% Sb2Te3 single crystal by adding 6 wt % excess Te, the hot-pressed 25% Bi2Te3-75% Sb2Te3 sinter exhibited the figure-of-merit of 2.97 × 10−3/K regardless of the excess Te amount.