The environmental impact resulting from the use of fossil fuel as an energy source affects the entire globe. Eventually, fossil fuels will no longer be a reasonable source of energy and alternative energy sources will be needed. Thermoelectric materials (TE) that directly convert heat into electricity are a viable option to replace the conventional fossil fuel because they are reliable, cost effective, and use no moving parts. Recently researchers discovered the existence of giant Seebeck coefficient in manganese oxide (MnO2) powders, which ignited an increased interest in MnO2-based materials. In this work we present a systematic structural and electrical characterization of amorphous and crystalline MnxOy thin films. These films were deposited at room temperature on heated silicon and sapphire substrates by DC Magnetron Sputtering. Our preliminary results show that MnxOy/silicon thin films undergo a crystalline change from Mn2O3 to Mn3O4 as annealing temperature is increased from 300°C to 500°C.

Research in the field of phase change materials (PCMs) requires that the temperature dependence of the thermal storage capacity be well known for the selection of PCMs as well as for simulation input. A differential scanning calorimeter (DSC) is often used, but it substantially misrepresents the true heat capacity in the vicinity of large-enthalpy phase transitions. Therefore, other suitable experimental techniques should be applied for the determination of the thermal storage capacity. Peltier-element-based adiabatic scanning calorimetry (pASC) measures the heat capacity and the enthalpy of PCMs in thermodynamic equilibrium, thus removing the rate dependence and deformation that are inherent to DSC. The technique is illustrated here by measurements on the pure alkane tricosane (C23), the commercial alkane mixture RT42 and its bound counterpart PX42.

Seebeck effect is widely used for the energy harvesting from wasted heat. In the Seebeck effect, the electric power can be generated by the temperature difference between both ends of the thermoelectric materials. However, low conversion efficiency is caused by heat flux from hot side to cold side of sample. In this paper, we have proposed a new thermal power generation mechanism with no temperature difference. We investigated the band structure of Ba8AuxSi46-x clathrate single crystal synthesized by Czochralski method. The single crystal has a gradient of the gold contents along the growth direction. According to the results of Seebeck coefficient, the electrical properties of the Ba8AuxSi46-x clathrate dramatically changed depending on the gold contents. In the case of gold content of lower than 5.33, the Ba8AuxSi46-x clathrate showed a n-type semiconductor. In the case of gold content of higher than 5.33, the Ba8AuxSi46-x clathrate showed a p-type semiconductor. The band gap of the n-type and p-type Ba8AuxSi46-x clathrate were wider than the intrinsic semiconductor. We can successfully synthesize a n-p junction single crystal, which obtaining energy band curve generated from the difference of Fermi level between p- and n- type semiconductors. The single crystal was heated under the uniform temperature and able to obtain generated electric voltage of around 0.6 mV at 400°C. These results suggested that the obtained electric voltage can be generated from the separation of hole-electron pair excited by heating at the intrinsic part with a narrow band gap along to the energy band curve formed by p-n junction.

Design and fabrication of hollow silicate micro-/ nanoparticles (HSMNP) with varied sizes and morphologies are of great interest especially in developing new generation of thermal insulation materials for building applications. Efficient energy use, simply called energy-saving, involves efforts to reduce the amount of energy required and recover wasted energy. This is important since building constitutes a substantial part in the total global energy consumption. Therefore, the current study is aimed at developing new HSMNP for thermal insulation application.

Thermoelectric properties of segmented nanowires and nanobelts are studied by means of the Kubo-Greenwood formula and a real-space renormalization plus convolution method. The tight-binding and Born models are respectively used for the calculation of electronic and lattice thermal conductivities. In particular, we investigate the thermoelectric figure of merit (ZT) of periodic and quasiperiodically segmented nanowires with two different cross sections, where the segments of the quasiperiodic one are ordered following the Fibonacci sequence. The results show an increase of ZT when the cross section area of nanowires diminishes. In addition, we present results of ZT in segmented nanobelts with an inhomogeneous cross section. For both nanowires and nanobelts, the quasiperiodicity seems to be an important enhancing factor of ZT.

In the previous work, it is reported that the Spin-Seebeck effect (SSE), which refer to the generation of a spin current from a temperature gradient, can be enhanced by Fe interface treatment. Here, we investigated the Fe thickness (dFe) dependency of spin-Seebeck voltage (VSSE) and mixing conductance (gr) in Pt/Fe/Bi:YIG/SGGG system. As a result, magnitude of VSSE had a peak at dFe ≓ 1 ML (monolayer , ≓ 0.3 mm), and also increase of gr was saturated at this point. It suggests that VSSE increase with increasing gr when dFe is smaller than 1.0 ML. For the case in which dFe is larger than 1.0ML, however, VSSE decreases due to a spin current decay in Fe layer with a constant gr. These experimental results are consistent with previous theoretical works.

A simplified procedure of synthesizing nano-sized hollow silicate particles (NHSPs) of 80-200 nm in average diameter and approximately 30 nm in wall thickness via (soft template) soluble-poly(methacrylic acid) sodium salt (NaPMA) is presented here. The process is easily scalable and can be carried out at ambient temperature. When deposited as thin (nanolayer) film, NHSPs show good transparency in visible spectra range and good sorption of CO2 for thermal energy efficiency especially in the field of thermal insulation application.

The magnesium compound Mg2Si and its solid solutions are expected as n-type thermoelectric (TE) material because they are non-toxic, have a large Clarke number, and are light weight. In this study, we improved TE performance by doping Ge into Sb-doped Mg2Si to cause phonon scattering and increase carrier concentration. A bulk of Sb-doped Si-Ge alloy as the raw material was fabricated using an arc-melting method. A high-purity Mg2Si was synthesized from metal Mg and Sb-doped Si-Ge alloy using spark plasma sintering equipment. For the samples with the same Sb concentration, the electrical conductivity was equivalent. On the other hand, the Seebeck coefficient was dependent on Ge concentration. Due to phonon scattering, thermal conductivity decreased by a small amount of Ge doping and κph dominated for thermal conduction. The minimum thermal conductivity of Mg2Si0.90Ge0.10 was 2.25 W/mK (κph: 2.06 W/mK, κel: 0.19 W/mK). The dimensionless figure of merit (ZT) for the Mg2Si0.945Ge0.05Sb0.005 sample was higher than that of the others due to reducing thermal conductivity and increasing carrier concentration. The maximum ZT was 0.47 at 713 K.

A study of Mg2Sn thin film material expected a high Thermo-Electrical (TE) characteristics in Room Temperature (RT) range is presented. The single phase (cubic crystal) Mg2Sn thin film is successfully formed on a glass substrate at 550 degree C with the conventional magnetron sputtering process when a metal layer of silver (Ag) or indium (In) of less than a hundred nanometer thickness is pre-coated before the deposition of Mg2Sn. The pre-coated material of Ag or In is diffused into the Mg2Sn film. P-type doping for the Mg2Sn by Ag is successful in this process, but n-type doping for the Mg2Sn film by In is not. In addition, it is found on Ag doping films that the Seebeck coefficient doesn’t decrease with the increase of the conductivity due to Ag doping which is different from the dependency of Ag doping in the bulk of Mg2Sn.

The formation of europium sulfides (Eu3S4 and EuS) via CS2 gas sulfurization of Eu2O3 powder was investigated. Single-phase Eu3S4 was obtained via CS2 gas sulfurization of Eu2O3 at 773 K for periods longer than 0.5 hr and EuS was generated by sulfurization at 1073 K for 8 hr. The higher sulfurization temperature and shorter sulfurization time accelerated the formation of high purity EuS. Synthetic pure Eu3S4 was treated under vacuum, rich-sulfur atmosphere and inert atmosphere, respectively. EuS was obtained when heat treatment was performed at 873 K under vacuum, at 973 K under CS2/Ar atmosphere, and at 1073 K under Ar atmosphere. Heat treatment of Eu3S4 generated a small amount of Eu2O2S due to impurity oxygen. Formation of Eu2O2S could be inhibited by heat treatment under CS2/Ar atmosphere.

Dimagnesium silicide is an eco-friendly thermoelectric compound whose constituent elements of both Mg and Si are non-toxic and exist in abundance on the earth. In this study, we attempted to control the thermal conductivity of Al-doped Mg2Si by grain refinement. Three types of Si powders, i.e., commercial coarse powder, its pulverized powder and commercial fine powder were prepared for synthesizing the Al-doped Mg2Si. Mg powder and one of the Si powders were weighed with Mg/Si mole ratio of 67/33, and mixed with Al powder with amount of 0.1 at.%. The Al-doped Mg2Si compounds were synthesized using three different Si powders via a liquid-solid phase reaction process under unified synthesizing conditions. A part of the synthesized Mg2Si powder using the coarse Si powder was pulverized. Four kinds of Mg2Si powders were sintered by pulse discharge sintering method under unified sintering conditions. The sintered samples of the synthesized Mg2Si powders made from the fine and the milled Si powders and of the milled Mg2Si powder had the grain-refined microstructure. Especially, the sintered sample of the milled Mg2Si powder was effective for grain refinement and for reduction of thermal conductivity, and had the best thermoelectric performance of ZT = 1.15 at 873 K.

The thermoelectric properties of polycrystalline samples of Sr1-xLa0.67xTiO3-δ and Sr0.20La0.53Ti1−yNbyO3-δ have been investigated. The first series has a gradually increasing amount of A-site vacancies, and charge carriers linked to the oxygen deficiency. The second series has a fixed amount of A-site vacancies (27%) and variation of the Nb content was used to optimise the electrical properties. Maximum power factors of 0.6 mW m-1 K-2 for x = 0.4 and 0.4 mW m-1 K-2 for y = 0.05 were observed at 700 K. Combining these values with thermal conductivity data obtained previously, suggests that maximum figures of merit zT = 0.16 for x = 0.4 and zT = 0.2 for y = 0.05 are possible at 1000 K. This study contributes new insight on the interplay between A-site vacancies and thermoelectric performance in SrTiO3.

The structural and electronic properties of lead chalcogenides PbX (X=S, Se, and Te) are investigated by first-principles calculations based on the range-separated hybrid functionals and semilocal generalized gradient approximation. It is found that an accurate band structure description requires the hybrid functional with the spin-orbit coupling included. Using this approach, the band structure of lead telluride and doped lead selenide are calculated, and its influences on the transport properties are discussed.