Showing papers by "Kunihito Koumoto published in 2020"
11 Feb 2020
TL;DR: Graphene has attracted intensive interests from broad areas of chemistry, physics, and materials science, among others as discussed by the authors, and interest in graphene's thermoelectric (TE) applications has engendered a larg...
Abstract: Graphene has attracted intensive interests from broad areas of chemistry, physics, and materials science, among others. Interest in graphene’s thermoelectric (TE) applications has engendered a larg...
65 citations
TL;DR: In this work, the composition of paper-supported silver selenide film was successfully modulated through changing reactant ratio and annealing treatment, and the power factor value of 2450.9 ± 364.4 μW/(mK2) at 303 K has been achieved, close to that of state-of-the-art bulk Ag2Se.
36 citations
TL;DR: This work successfully fabricated n-type Mg3Sb2-based materials using an inexpensive and efficient approach of one-step ball milling and spark plasma sintering, and demonstrates that complementary and favorable effect of multiple elements co-alloying/-doping leads to an excellent thermoelectric performance.
Abstract: Mg3Sb2-based compounds by virtue of nontoxicity and low-cost have become a promising class of candidates for midtemperature thermoelectric power generation. Here, we successfully fabricated n-type Mg3Sb2-based materials using an inexpensive and efficient approach of one-step ball milling and spark plasma sintering, and demonstrate that a complementary and favorable effect of multiple elements coalloying/-doping leads to an excellent thermoelectric performance. The intrinsic p-type conducting behavior for Mg3Sb2 could be changed to n-type through Bi and Se coalloying on Sb sublattices with excess Mg, resulting from the suppression of Mg vacancies and the formation of Mg interstitial. Furthermore, Mn doping on Mg sublattices could soften the chemical bonds, leading to the increase of carrier mobility and concentration simultaneously. Additionally, multielement coalloying/-doping could significantly increase the lattice disorder, which undoubtedly strengthens the phonon scattering and readily results in a suppressed lattice thermal conductivity. As a result, a highest ZT value of 1.6 at 723 K and an average ZT value up to 1.1 were obtained in the temperature range of 323-723 K in the Mg3.18Mn0.02Sb1.5Bi0.49Se0.01 sample, which is one of the highest values among the Te free Mg3Sb2. This work could give guidance for improving the thermoelectric performance of Zintl phase materials or even others using the multielement codoping/-alloying strategy.
23 citations
TL;DR: A solution-based strategy to fabricate a large-area foil of hybrid TaS2 /organic superlattice, where [TaS2 ] monolayers and organic molecules alternatively stack in atomic scale, can add a new dimension to manipulate the structure and properties of 2D materials and provide new opportunities for flexible nanoelectronic devices.
Abstract: TaS2 nanolayers with reduced dimensionality show interesting physics, such as a gate-tunable phase transition and enhanced superconductivity, among others. Here, a solution-based strategy to fabricate a large-area foil of hybrid TaS2 /organic superlattice, where [TaS2 ] monolayers and organic molecules alternatively stack in atomic scale, is proposed. The [TaS2 ] layers are spatially isolated with remarkably weakened interlayer bonding, resulting in lattice vibration close to that of TaS2 monolayers. The foil also shows excellent mechanical flexibility together with a large electrical conductivity of 1.2 × 103 S cm-1 and an electromagnetic interference of 31 dB, among the highest values for solution-processed thin films of graphene and inorganic graphene analogs. The solution-based strategy reported herein can add a new dimension to manipulate the structure and properties of 2D materials and provide new opportunities for flexible nanoelectronic devices.
18 citations
TL;DR: Layered 1T-type TiS2 powders were pre-treated by an ethanol-based shear pulverization process, which showed outstanding effectiveness in reducing the average grain size and narrowing the size distribution while maintaining high crystallinity and plate-shaped morphology, indicating clearly the significant effect of texture engineering on the TE performance.
Abstract: Layered 1T-type TiS2 powders were pretreated by an ethanol-based shear pulverization process, which showed outstanding effectiveness in reducing the average grain size and narrowing the size distribution while maintaining high crystallinity and plate-shaped morphology. The resulting bulk ceramics densified by spark plasma sintering possessed a highly (00l)-oriented texture and pronounced anisotropy. They showed a noticeably increased σ and an unaffected S in the in-plane direction due to the increased carrier mobility μ and the constant carrier concentration n, which resulted in a significant enhancement of the in-plane power factor, optimally to an unprecedented high level of 1.6-1.8 mW m-1 K-2 in a range of 323-673 K. Meanwhile, the lattice thermal conductivity was reduced by approximately 20% due to the intensified grain boundary phonon scattering that overwhelmed the effect due to texturing. These effects not only demonstrated the powder shear pulverization pretreatment as a facial and reliable route toward a high-textured TiS2 but also enabled a remarkable increase of ZT record for TiS2-based thermoelectrics (TEs) to approximately 0.7 at 673 K, indicating clearly the significant effect of texture engineering on TE performance.
16 citations
13 Jul 2020
TL;DR: In this article, the effect of aluminum dopant at the concentration range 0.5 − 3 mol % on the structural and TE properties has been investigated in more details, and the optimum concentration of Al for better TE performance is found to be 2 mol %, which could significantly increase the electrical conductivity and reduce the thermal conductivity of ZnO NSs and thus enhance the TE performance.
Abstract: Microwave irradiation is found to be effective to provide highly crystalline nanostructured materials. In this work, this technique has been used to produce highly improved thermoelectric (TE) material based on aluminum (Al) doped zinc oxide (ZnO) nanostructures (NSs). The effect of Al dopant at the concentration range 0.5–3 mol % on the structural and TE properties has been investigated in more details. The optimum concentration of Al for better TE performance is found to be 2 mol %, which could significantly increase the electrical conductivity and reduce the thermal conductivity of ZnO NSs and thus enhance the TE performance. This concentration showed almost metallic conductivity behavior for ZnO NSs at low temperatures, e.g., below 500 K. The electrical conductivity reached 400 S/m at room temperature, which is around 200 times greater than the value recorded for the pure ZnO NSs. Remarkably, the measured room temperature thermal conductivity of the microwave synthesized ZnO NSs was very low, which is around 4 W/m·K. This value was further reduced to 0.5 W/m·K by increasing the Al doping to 3 mol %. The figure of merit recorded 0.028 at 675 K, which is 15 times higher than that of the pure ZnO NSs. The output power of a single leg module made of 2 mol % Al doped ZnO NSs was 3.7 µW at 485 K, which is higher by 8 times than that of the pure sample. These results demonstrated the advantage of the microwave irradiation rout as a superior synthetic technique for producing and doping promising TE nanomaterials like ZnO NSs.
7 citations
TL;DR: Polycrystalline bulk of TiS2 with a remarkable enhancement of the texture degree was obtained by densifying powders refined by a liquid-based mechanical exfoliation process, and a tremendously high power factor of up to 16 μW cm-1 K-2 at 673 K was achieved, which is the highest for bulkTiS2 at high temperatures.
7 citations
TL;DR: In this article, a joint project was co-funded by the King Abdulaziz University (KAU), Jeddah, and King Abdullah University of Science and Technology (KAUST), Thuwal, under Grant No. JP-19-002.
Abstract: This joint project was co-funded by the King Abdulaziz University (KAU), Jeddah, and King Abdullah University of Science and Technology (KAUST), Thuwal, under Grant No. JP-19-002. The authors, therefore, acknowledge KAU and KAUST for their technical and financial support.
6 citations
TL;DR: In this article, the Tb-doped sample was found to have the highest TE power factor and Figure of merit values at room temperature (RT) thermoelectric (TE) materials.
6 citations