K. Malik

Sb concentration dependent structural and resistive properties of polycrystalline Bi-Sb alloys

Polycrystalline Bi1−xSbx alloys have been synthesized over a wide range of antimony concentration (0.08 ≤ x ≤ 0.20) by solid state reaction method. In depth structural analysis using x-ray diffraction (XRD) and temperature dependent resistivity (ρ) measurement of synthesized samples have been performed. XRD data confirmed single phase nature of polycrystalline samples and revealed that complete solid solution is formed between bismuth and antimony. Rietveld refinement technique, utilizing maud software, has been used to perform detailed structural analysis of the samples and lattice parameters of polycrystalline Bi1−xSbx alloys have been estimated. Lattice parameter and unit cell volume decreases monotonically with increasing antimony content. The variation of lattice parameters with antimony concentration depicts a distinct slope change at x = 0.12. Band gap (Eg) has been estimated from the thermal variation of resistivity data, with the 12% Sb content sample showing maximum Eg. It has been observed that...

Temperature-dependent structural property and power factor of n type thermoelectric Bi0.90Sb0.10 and Bi0.86Sb0.14 alloys

Thermal variation of structural property, linear thermal expansion coefficient (α), resistivity (ρ), thermopower (S), and power factor (PF) of polycrystalline Bi1-xSbx (x = 0.10 and 0.14) samples are reported. Temperature-dependent powder diffraction experiments indicate that samples do not undergo any structural phase transition. Rietveld refinement technique has been used to perform detailed structural analysis. Temperature dependence of α is found to be stronger for Bi0.90Sb0.10. Also, PF for direct band gap Bi0.90Sb0.10 is higher as compared to that for indirect band gap Bi0.86Sb0.14. Role of electron-electron and electron-phonon scattering on ρ, S, and PF has been discussed.

Magneto-resistive property study of direct and indirect band gap thermoelectric Bi-Sb alloys

We report magneto-resistive properties of direct and indirect band gap Bismuth-Antimony (Bi-Sb) alloys. Band gap increases with magnetic field. Large positive magnetoresistance (MR) approaching to 400% is observed. Low field MR experiences quadratic growth and at high field it follows a nearly linear behavior without sign of saturation. Carrier mobility extracted from low field MR data depicts remarkable high value of around 5 m2V−1s−1. Correlation between MR and mobility is revealed. We demonstrate that the strong nearly linear MR at high field can be well understood by classical method, co-build by Parish and Littlewood, Nature 426, 162 (2003) and Phys. Rev. B 72, 094417 (2005).

Tuning of thermoelectric properties with changing Se content in Sb2Te3

Polycrystalline Sb2Te3−x Se x samples were synthesized by the solid-state reaction method. The structural analysis showed that up to the maximal concentration of Se, the samples possess rhombohedral crystal symmetry (space group ). The increase of Se content increases the resistivity of the samples. The variation of phonon frequencies, observed from the Raman spectroscopic study, depicts an anomalous behaviour around . The sample Sb2Te2.8Se0.2 also shows maximum Seebeck coefficient, carrier concentration and thermoelectric power factor. The nature of the scattering mechanism controlling the thermopower data has been explored. The thermoelectric properties of the synthesized materials have been analyzed theoretically in the frame of the Boltzmann equation approach.

Thermoelectric property study of Bi2Te3-Sb2Te3 mixed crystals

Polycrystalline Bi2Te3-Sb2Te3 mixed crystals are synthesized by solid state reaction method. Structural characterizations are carried out using X-Ray diffraction (XRD). Thermal variation of resistivity data, measured down to 10K, shows that there is a transition from semiconducting to metallic behavior for 80% Sb containing sample. Temperature dependent thermopower measurement is carried out using differential technique in the temperature range 300–20 K. Thermopower data shows all the samples are p-type in nature. Power factor of the samples are also estimated.

Evidence of iso-structural phase transition in rhombohedral Bi-Sb alloy

Temperature-dependent structural studies of polycrystalline Bi1−x Sb x alloys were carried out using synchrotron x-ray diffraction. In-depth powder diffraction analysis reveals that an iso-structural phase transition takes place in the rhombohedral Bi-Sb alloy around 200 K, which is accompanied by anomalous behavior in the temperature-dependent linear thermal expansion data. In addition, the thermal variation of refined isotropic thermal parameters or Debye-Waller factor (B iso), ratio of the lattice parameters and Debye temperature indicates that anisotropy, arising due to local structural disorder, plays a significant role in this material.

Structural and thermoelectric property study of Se doped Sb2Te3 alloy

In depth structural analysis of the polycrystalline Sb2Te3-xSex alloy has been done by Rietveld refinement technique using MAUD software. Thermal variation of resistivity measurement is performed down to 10 K. Temperature dependent thermopower, measured in the range 300-20 K, reveals that samples are p-type in nature. Power factor has been estimated using resistivity and thermopower data.

Effect of antimony concentration on structural and transport properties of (Bi1-xSbx)2Te3 mixed crystal

Polycrystalline (Bi1-xSbx)2Te3 (0.60≤x≤0.68) alloys have been synthesized by solid state reaction method. Structural characterizations have been done using X-Ray Diffraction (XRD). Lattice parameter decreases with antimony (Sb) concentration. Sb doping leads to the modification in band structure and Fermi surface geometry. Band gap calculated from thermal variation of resistivity (ρ-T) data, decreases with Sb concentration. Sb concentration dependent power factor near room temperature have been calculated from obtained resistivity and thermopower data. Highest power factor obtained for (Bi0.40Sb0.60)2Te3 alloy.

Structural and transport properties of metallic and semiconducting Sb2Te3 alloy

Metallic and semiconducting Sb2Te3 alloys have been synthesized by controlling the cooling rate in the solid state reaction method. Temperature dependent resistivity is measured down to 10 K for the identification of metallic and semiconducting phases. Structural studies are performed by both X-ray diffraction (XRD) and Raman spectroscopic analyses. XRD study confirms single phase nature of polycrystalline alloys in the detectable limit. Raman spectroscopy is used to understand the vibration properties of Sb2Te3 crystals. Widening of full width at half maxima of the highest intense peak in the XRD analysis indicates higher amount of defects in the semiconducting phase than that in the metallic one. Raman study indicates presence of impurity phases in the semiconducting Sb2Te3. The resistivity of semiconducting Sb2Te3 sample is higher than that of metallic one, which corroborates with the XRD and Raman analyses.

Sb concentration dependent power factor of n-type thermoelectric material Bi1−xSbx alloy

We report the correlation between structural data and transport property, viz, resistivity (ρ) and Seebeck Coefficient (Thermopower, S) of n-type thermoelectric material, Bi1−xSbx (0.08≤x≤0.20) alloy. Rietveld refinement technique has been used to estimate structural parameters. Thermal variation of ρ and S has been measured and the band gap (Eg) of these narrow gap semiconductors has been estimated. Correlation between structural and transport property has been established and dependence of Sb concentration on the Power Factor (PF=S2/ρ) has been revealed.