Sivaiah Bathula

Enhanced thermoelectric figure-of-merit in spark plasma sintered nanostructured n-type SiGe alloys

We report a significant enhancement in the thermoelectric figure-of-merit of phosphorous doped nanostructured n-type Si80Ge20 alloys, which were synthesized employing high energy ball milling followed by rapid-heating using spark plasma sintering. The rapid-heating rates, used in spark plasma sintering, allow the achievement of near-theoretical density in the sintered alloys, while retaining the nanostructural features introduced by ball-milling. The nanostructured alloys display a low thermal conductivity (2.3 W/mK) and a high value of Seebeck coefficient (−290 μV/K) resulting in a significant enhancement in ZT to about 1.5 at 900 °C, which is so far the highest reported value for n-type Si80Ge20 alloys.

Thermoelectric properties of Cu3SbSe3 with intrinsically ultralow lattice thermal conductivity

We report the synthesis, characterization and evaluation of the thermoelectric properties of Cu3SbSe3 with a view to explore its utility as an useful thermoelectric material due to its intrinsically low thermal conductivity. Cu3SbSe3 was synthesized employing a solid state reaction process followed by spark plasma sintering, and the synthesized material was extensively characterized for its phase, composition and structure, which suggested formation of a single-phase. The measured electrical transport properties of Cu3SbSe3 indicated p-type conduction in this material. The electrical transport behavior agrees well with that predicted theoretically using first-principle density-functional theory calculations, employing generalized gradient approximation. The measured thermal conductivity was found to be 0.26 W m−1 K−1 at 550 K, which is the lowest reported thus far for Cu3SbSe3 and is among the lowest for state-of-the-art thermoelectric materials. Despite its ultralow thermal conductivity coupled with a moderate Seebeck coefficient, the calculated value of its thermoelectric figure-of-merit was found to be exceptionally low (<0.1), which was primarily attributed to its low electrical conductivity. Nevertheless, it is argued that Cu3SbSe3, due its environmentally-friendly constituent elements, ultralow thermal conductivity and moderate thermopower, could be a potentially useful thermoelectric material as the power factor can be favorably tailored by tuning the carrier concentration using suitable metallic dopants.

Thermoelectric and mechanical properties of spark plasma sintered Cu3SbSe3 and Cu3SbSe4: Promising thermoelectric materials

We report the synthesis of thermoelectric compounds, Cu3SbSe3 and Cu3SbSe4, employing the conventional fusion method followed by spark plasma sintering. Their thermoelectric properties indicated that despite its higher thermal conductivity, Cu3SbSe4 exhibited a much larger value of thermoelectric figure-of-merit as compared to Cu3SbSe3, which is primarily due to its higher electrical conductivity. The thermoelectric compatibility factor of Cu3SbSe4 was found to be ∼1.2 as compared to 0.2 V−1 for Cu3SbSe3 at 550 K. The results of the mechanical properties of these two compounds indicated that their microhardness and fracture toughness values were far superior to the other competing state-of-the-art thermoelectric materials.

Microstructure and mechanical properties of thermoelectric nanostructured n-type silicon-germanium alloys synthesized employing spark plasma sintering

Owing to their high thermoelectric (TE) figure-of-merit, nanostructured Si80Ge20 alloys are evolving as a potential replacement for their bulk counterparts in designing efficient radio-isotope TE generators. However, as the mechanical properties of these alloys are equally important in order to avoid in-service catastrophic failure of their TE modules, we report the strength, hardness, fracture toughness, and thermal shock resistance of nanostructured n-type Si80Ge20 alloys synthesized employing spark plasma sintering of mechanically alloyed nanopowders of its constituent elements. These mechanical properties show a significant enhancement, which has been correlated with the microstructural features at nano-scale, delineated by transmission electron microscopy.

EM shielding effectiveness of Pd-CNT-Cu nanocomposite buckypaper

We report the synthesis of a nanocomposite consisting of Pd doped multiwall carbon nanotubes decorated with Cu nanoparticles, as a lightweight and flexible microwave absorbing material, using an electroless technique. The synthesised nanocomposite was extensively characterized by employing X-ray diffraction, Raman spectroscopy, FESEM, and HRTEM and their results were correlated with the high electromagnetic interference (EMI) shielding observed in the present study. The optimum dielectric properties coupled with good electrical conductivity of this nanocomposite contribute to designing this absorption-based microwave shield, which exhibited a good EMI shielding effectiveness (EMI SE) of ∼35 dB at a thickness of 200 μm, resulting in a high specific EMI SE of ∼108 dB cm3 g−1 in the Ku-band.

Nanoindentation and Wear Characteristics of Al 5083/SiCp Nanocomposites Synthesized by High Energy Ball Milling and Spark Plasma Sintering

Al 5083/10 wt% SiC p nano composites have been synthesized by means of high energy ball milling followed by spark plasma sintering (SPS). Nano composites produced via this method exhibited near-theoretical density while retaining the nano-grained features. X-ray diffraction (XRD) analysis indicated that the crystalline size of the ball milled Al 5083 matrix was observed to be ∼25 nm and it was coarsened up to ∼30 nm after SPS. Nano indentation results of nano composites demonstrated a high hardness of ∼280 HV with an elastic modulus of 126 GPa. Wear and friction characteristics with addition of SiC p reinforcement exhibited significant improvement in terms of coefficient of friction and specific wear rate to that of nano structured Al 5083 alloy. The reduction in specific wear rate in the nanocomposite was mainly due to the change of wear mechanism from adhesive to abrasive wear with the addition of SiC P which resulted in high hardness associated with nano-grained microstructure.

Electrical transport and mechanical properties of thermoelectric tin selenide

Motivated by the unprecedented thermoelectric performance of SnSe, we report its band structure calculations, based on density functional theory using the full potential linearized augmented plane wave. These calculations were further extended to evaluate the electrical transport properties using Boltzmann transport theory and the results were compared with the as-synthesized polycrystalline counterpart, which was synthesized employing conventional vacuum melting technique followed by consolidation employing spark plasma sintering. The as-synthesized SnSe was thoroughly characterized employing XRD, FESEM and TEM for phase purity, morphology and structure. The theoretically predicted band gap values and the temperature dependence of the electrical transport properties of SnSe were in reasonable agreement with the experimental results, within the approximations employed in our theoretical calculations. These theoretical calculations suggested that the optimum thermoelectric performance in SnSe is expected to occur at a hole doping concentration of ∼3 to 5 × 1021 cm−3. The measured fracture toughness and hardness of SnSe were found to be ∼0.76 ± 0.05 MPa √m and 0.27 ± 0.05 GPa, respectively, which are comparable with other state-of-the-art thermoelectric materials. The high value of thermal shock resistance ∼252 ± 9 W m−1, coupled with its good mechanical properties suggests SnSe to be a potential material for thermoelectric device applications.

Band structure and transport studies of copper selenide: An efficient thermoelectric material

We report the band structure calculations for high temperature cubic phase of copper selenide (Cu2Se) employing Hartree-Fock approximation using density functional theory within the generalized gradient approximation. These calculations were further extended to theoretically estimate the electrical transport coefficients of Cu2Se employing Boltzmann transport theory, which show a reasonable agreement with the corresponding experimentally measured values. The calculated transport coefficients are discussed in terms of the thermoelectric (TE) performance of this material, which suggests that Cu2Se can be a potential p-type TE material with an optimum TE performance at a carrier concentration of ∼ 4−6×1021cm−3.

Physico-mechanical and Surface Wear Assessment of Magnesium Oxide Filled Ceramic Composites for Hip Implant Application

In the present study, applicability of ceramic composites as ceramic-on-ceramic hip prostheses is explored. Hence, ceramic composites containing zirconium oxide, silicon nitride, chromium oxide by varying proportion of aluminum oxide and magnesium oxide were prepared by spark plasma sintering and subsequently characterized for their physico-mechanical and tribological properties. The physico-mechanical and tribological properties of the fabricated composites were evaluated by measuring their density, void content, indentation response, fracture toughness and wear resistance respectively. The mechanical properties and wear performance of the composites are significantly improved with the addition of magnesium oxide content. Experimental results indicated that the 3 wt.% magnesium oxide based hip implant composite showed highest hardness, highest fracture toughness, highest young’s modulus with lowest wear rate. A maximum increase of approximately 44% in nanohardness, 14% in Young’s modulus, 98% in fracture toughness and 75% in wear resistance are achieved by introducing 3 wt.% magnesium oxide content. The experimental results indicated that fabricated ceramic composites will stand out as a promising material for hip implant substitution.