Enhanced magnetic and thermoelectric properties in epitaxial polycrystalline SrRuO3 thin film

Transition metal oxide thin films show versatile electrical, magnetic, and thermal properties which can be tailored by deliberately introducing macroscopic grain boundaries via polycrystalline solids. In this study, we focus on the modification of the magnetic and thermal transport properties by fabricating single- and polycrystalline epitaxial SrRuO3 thin films using pulsed laser epitaxy. Using epitaxial stabilization technique with atomically flat polycrystalline SrTiO3 substrate, epitaxial polycrystalline SrRuO3 thin film with crystalline quality of each grain comparable to that of single-crystalline counterpart is realized. In particular, alleviated compressive strain near the grain boundaries due to coalescence is evidenced structurally, which induced enhancement of ferromagnetic ordering of the polycrystalline epitaxial thin film. The structural variations associated with the grain boundaries further reduce the thermal conductivity without deteriorating the electronic transport, and lead to enhanced thermoelectric efficiency in the epitaxial polycrystalline thin films, compared with their single-crystalline counterpart.Comment: 24 pages, 5 figure

Enhanced magnetic and thermoelectric properties in epitaxial polycrystalline SrRuO3 thin film

Transition metal oxide thin films show versatile electrical, magnetic, and thermal properties which can be tailored by deliberately introducing macroscopic grain boundaries via polycrystalline solids. In this study, we focus on the modification of the magnetic and thermal transport properties by fabricating single- and polycrystalline epitaxial SrRuO3 thin films using pulsed laser epitaxy. Using epitaxial stabilization technique with atomically flat polycrystalline SrTiO3 substrate, epitaxial polycrystalline SrRuO3 thin film with crystalline quality of each grain comparable to that of single-crystalline counterpart is realized. In particular, alleviated compressive strain near the grain boundaries due to coalescence is evidenced structurally, which induced enhancement of ferromagnetic ordering of the polycrystalline epitaxial thin film. The structural variations associated with the grain boundaries further reduce the thermal conductivity without deteriorating the electronic transport, and lead to enhanced thermoelectric efficiency in the epitaxial polycrystalline thin films, compared with their single-crystalline counterpart.Comment: 24 pages, 5 figure

Boundary Engineering for the Thermoelectric Performance of Bulk Alloys Based on Bismuth Telluride

Thermoelectrics, which transports heat for refrigeration or converts heat into electricity directly, is a key technology for renewable energy harvesting and solid-state refrigeration. Despite its importance, the widespread use of thermoelectric devices is constrained because of the low efficiency of thermoelectric bulk alloys. However, boundary engineering has been demonstrated as one of the most effective ways to enhance the thermoelectric performance of conventional thermoelectric materials such as Bi2Te3, PbTe, and SiGe alloys because their thermal and electronic transport properties can be manipulated separately by this approach. We review our recent progress on the enhancement of the thermoelectric figure of merit through boundary engineering together with the processing technologies for boundary engineering developed most recently using Bi2Te3-based bulk alloys. A brief discussion of the principles and current status of boundary-engineered bulk alloys for the enhancement of the thermoelectric figure of merit is presented. We focus mainly on (1) the reduction of the thermal conductivity by grain boundary engineering and (2) the reduction of thermal conductivity without deterioration of the electrical conductivity by phase boundary engineering. We also discuss the next potential approach using two boundary engineering strategies for a breakthrough in the area of bulk thermoelectric alloys. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim120221sciescopu

Electronic and Thermal Transport Properties of Complex Structured Cu-Bi-Se Thermoelectric Compound with Low Lattice Thermal Conductivity

Monoclinic Cux+yBi5−ySe8 structure has multiple disorders, such as randomly distributed substitutional and interstitial disorders by Cu as well as asymmetrical disorders by Se. Herein, we report the correlation of electronic and thermal properties with the structural complexities of Cux+yBi5−ySe8. It is found that the interstitial Cu site plays an important role not only to increase the electrical conductivity due to the generation of electron carriers but also to reduce the thermal conductivity mainly due to the phonon scattering by mass fluctuation. With impurity doping at the interstitial Cu site, an extremely low lattice thermal conductivity of 0.32 W·m−1·K−1 was achieved at 560 K. These synergetic effects result in the enhanced dimensionless figure of merit (ZT)

Direct Observation of Inherent Atomic-Scale Defect Disorders responsible for High-Performance Ti1-xHfxNiSn1-ySby Half-Heusler Thermoelectric Alloys

Structural defects often dominate the electronic- and thermal-transport properties of thermoelectric (TE) materials and are thus a central ingredient for improving their performance. However, understanding the relationship between TE performance and the disordered atomic defects that are generally inherent in nanostructured alloys remains a challenge. Herein, the use of scanning transmission electron microscopy to visualize atomic defects directly is described and disordered atomic-scale defects are demonstrated to be responsible for the enhancement of TE performance in nanostructured Ti1-xHfxNiSn1-ySby half-Heusler alloys. The disordered defects at all atomic sites induce a local composition fluctuation, effectively scattering phonons and improving the power factor. It is observed that the Ni interstitial and Ti,Hf/Sn antisite defects are collectively formed, leading to significant atomic disorder that causes the additional reduction of lattice thermal conductivity. The Ti1-xHfxNiSn1-ySby alloys containing inherent atomic-scale defect disorders are produced in one hour by a newly developed process of temperature-regulated rapid solidification followed by sintering. The collective atomic-scale defect disorder improves the zT to 1.09 +/- 0.12 at 800 K for the Ti0.5Hf0.5NiSn0.98Sb0.02 alloy. These results provide a promising avenue for improving the TE performance of state-of-the-art materials. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

Formation of Dense Pore Structure by Te Addition in Bi0.5Sb1.5Te3: An Approach to Minimize Lattice Thermal Conductivity

We herein report the electronic and thermal transport properties of p-type Bi0.5Sb1.5Te3 polycrystalline bulks with dense pore structure. Dense pore structure was fabricated by vaporization of residual Te during the pressureless annealing of spark plasma sintered bulks of Te coated Bi0.5Sb1.5Te3 powders. The lattice thermal conductivity was effectively reduced to the value of 0.35 W m−1 K−1 at 300 K mainly due to the phonon scattering by pores, while the power factor was not significantly affected. An enhanced ZT of 1.24 at 300 K was obtained in spark plasma sintered and annealed bulks of 3 wt.% Te coated Bi0.5Sb1.5Te3 by these synergetic effects

A strategy to overcome the limits of carbon-based materials as lithium-ion battery anodes

The free-standing Si-coated carbon nanofiber (Si/CNF) mat was fabricated for the anode of lithium ion battery through combining electrospun CNF mat with electrodeposited Si layer. Spaghetti or granule-like Si was obtained by varying the deposition conditions. This Si/CNF mat was directly used as an active material and a current collector as well, which involves neither binders nor additional metal substrate. The best performance was achieved in spaghetti-like Si due to its highly porous nature which can accommodate volume expansion and large surface area which benefit the efficient charge transfer both at Si/CNF interface and at the electrode/electrolyte interface. The optimized Si/CNF mat after annealing at 1000 C delivered a capacity of 870 mA h g1 at 1st discharge and 730 mA h g1 at 50th discharge with a capacity retention of 84%, improving the capacity of pure CNF (280 mA h g1 at the 50th discharge) by almost three times. In addition, corrosion of the current collector no longer exists in our approach. Our X-ray photoemission spectroscopy and electrochemical analysis revealed that the formation of Si–C bond through high temperature annealing can enhance the adhesion between silicon and carbon at the interface which benefits the cyclic performance of anode ultimately.1771sciescopu

Fe-Doping Effect on Thermoelectric Properties of p-Type Bi0.48Sb1.52Te3

The substitutional doping approach has been shown to be an effective strategy to improve ZT of Bi2Te3-based thermoelectric raw materials. We herein report the Fe-doping effects on electronic and thermal transport properties of polycrystalline bulks of p-type Bi0.48Sb1.52Te3. After a small amount of Fe-doping on Bi/Sb-sites, the power factor could be enhanced due to the optimization of carrier concentration. Additionally, lattice thermal conductivity was reduced by the intensified point-defect phonon scattering originating from the mass difference between the host atoms (Bi/Sb) and dopants (Fe). An enhanced ZT of 1.09 at 300 K was obtained in 1.0 at% Fe-doped Bi0.48Sb1.52Te3 by these synergetic effects

Highly fluidic liquid at homointerface generates grain-boundary dislocation arrays for high-performance bulk thermoelectrics

Dislocation arrays embedded in low-angle grain-boundaries have emerged as an effective structural defect for a dramatic improvement of thermoelectric performance by reducing thermal conductivity [1] A transient liquid-flow assisted compacting process has been employed for p-type Bi0.5Sb1.5Te3 material to generate the dislocation arrays at grain-boundaries. The details of underlying formation mechanism are crucial for the feasibility of the process on other state-of-the-art thermoelectric materials but have not been well understood. Here, we report the direct observation of dislocation formation process at grain-boundaries of Sb2Te3 system as a proof-of-concept material. We found that the formation of homointerface between Te-terminated Sb2Te3 matrix phase and Te liquid atomic-layer of secondary phase is a prerequisite factor to achieve the low-energy liquid-solid homointerface at compacting elevated temperature. We further demonstrate from the successful observations of atomic structure in the intermediate state of the compacted pellet that the high self-diffusion rate of Te atoms at the liquid-solid homointerface facilitates an effective grain rearrangement, generating low-energy grain-boundaries embedded with dense dislocation arrays. These results pave the way to improve thermoelectric performance of various materials where dislocation arrays are generated by transient liquid-flow assisted compacting process using precursors with an interface constructed with the same types of atoms. (C) 2018 Published by Elsevier Ltd on behalf of Acta Materialia In