Co-reporter:Jie Gao;Chengyan Liu;Xiaoyang Wang;Yu Chen
Journal of Electronic Materials 2016 Volume 45( Issue 3) pp:1290-1295
Publication Date(Web):2016 March
DOI:10.1007/s11664-015-4000-5
With high carrier mobility and low cost, reduced graphene oxide (RGO) shows bright prospects for use in the field of thermoelectric materials. To investigate the intrinsic thermoelectric properties of RGO sheets, we prepared RGO papers which were reduced by HBr solution for 5 min, 20 min, and 60 min, respectively. Thermogravimetry analysis (TGA) and Raman analysis showed that the conjugated carbon network of graphene oxide (GO) was restored during the reduction process and the thermal stability of the RGO papers was much better than that of GO paper. The RGO paper that was reduced for 60 min and then annealed in Ar/H2 atmosphere exhibited the highest electrical conductivity of 3.22 × 105 S/m at 160°C. As the reduction degree of the RGO paper deepens, the Seebeck coefficient gradually transforms from positive to negative, indicating that the conduction type of RGO paper can be controlled by regulating the reduction degree.
Co-reporter:Ru Chen, Lei Miao, Haoliang Cheng, Eiji Nishibori, Chengyan Liu, Toru Asaka, Yuji Iwamoto, Masaki Takata and Sakae Tanemura
Journal of Materials Chemistry A 2015 vol. 3(Issue 7) pp:3726-3738
Publication Date(Web):19 Dec 2014
DOI:10.1039/C4TA05559D
Pure phase V1−xWxO2(M/R) nanorods with superb metal–insulator transition properties were obtained in tungsten (W)-doped level ranges from 0.5 to 2.0 at% using a one-step hydrothermal treatment without additional annealing steps. The assured level of W doping greatly promotes the grain growth of pure phase vanadium oxide (VO2)(M/R) and simultaneously the phase transition temperature (Tc) is depressed as much as 103 °C per at% W for the V1−xWxO2 nanorods when x = 1.0–2.0 at%. After mixing the pure phase VO2(M) (W-doped 0.5 at%, phase transition at 47 °C) nanorods with acrylic resin, the integrated visible transmission of the VO2 composite coating on glass is up to 60.6% and the integrated solar modulation efficiency is up to 10.3%. These results mean that the superior thermochromic property will greatly favor the practical application of VO2-based smart windows.
Co-reporter:Heng Quan Yang, Lei Miao, Cheng Yan Liu, Chao Li, Sawao Honda, Yuji Iwamoto, Rong Huang, and Sakae Tanemura
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 26) pp:14263
Publication Date(Web):June 10, 2015
DOI:10.1021/acsami.5b02504
Antimony telluride (Sb2Te3) and its based alloys are of importance to p-type semiconductors for thermoelectric applications near room temperature. Herein, we report a simple, low-energy intensive, and scalable surfactant-assisted reflux method for the synthesis of Sb2Te3 nanoparticles in the solvent ethylene glycol (EG) at low temperatures (120–180 °C). The formation mechanism of platelike Sb2Te3 nanoparticles is proposed. Also, it is found that the size, shape, and chemical composition of the products could be controlled by the introduction of organic surfactants (CTAB, PVP, etc.) or inorganic salts (EDTA-Na2, NaOH, etc.). Additionally, the collected Sb2Te3 nanoparticles were further fabricated into nanostructured pellets using cold-compaction and annealing techniques. Low resistivity [(7.37–19.4) × 10–6 Ω m], moderate Seebeck coefficient (103–141 μV K–1), and high power factor (10–16 × 10–4 W m–1 K–2) have been achieved in our Sb2Te3-nanostructured bulk materials. The relatively low thermal conductivity (1.32–1.55 W m–1 K–1) is attained in the nanobulk made of PVP-modified nanoparticles, and values of ZT in the range of 0.24–0.37 are realized at temperatures ranging from 50 to 200 °C. Our researches set forth a new avenue in promoting practical applications of Sb2Te3-based thermoelectric power generation or cooling devices.Keywords: antimony telluride; growth mechanism; reflux method; thermoelectric materials; transport properties;
Co-reporter:Chengyan Liu, Lei Miao, Jianhua Zhou, Rong Huang, Craig A. J. Fisher, and Sakae Tanemura
The Journal of Physical Chemistry C 2013 Volume 117(Issue 22) pp:11487-11497
Publication Date(Web):May 7, 2013
DOI:10.1021/jp401132g
A novel, fast combustion method for synthesizing anatase TiO2 nanoparticles (average diameter ∼14 nm) codoped with N and Nb in a single step is reported. XRD, STEM-EDX, and XPS measurements confirm that Nb ions are incorporated into the tetragonal lattice on Ti sites, while N ions occupy O sites, and likely also interstitial sites. Sintering of pellets of codoped powders under reducing conditions produced polycrystalline samples with the rutile structure. Chemically tuned samples have power factors up to 9.87 × 10–4 W m–1 K–2, 7 times higher than that of pure TiO2 sintered under the same conditions. In addition, the thermal conductivity is considerably lower at 2.6–4.0 W m–1 K–1 as a result of greater grain-boundary and point-defect scattering. The figure of merit, ZT, is improved to 0.35 at 700 °C, which is the highest value reported for a TiO2 material to date, and is comparable to the highest values of any n-type thermoelectric oxide. Our material also exhibits good thermal stability in a pure N2 atmosphere and is an excellent candidate for thermoelectric power generators. Consequently, the combustion technique represents a promising new strategy for preparing foreign-atom-doped metal oxides; the chemical tuning approach, a combination of foreign-atom-doped nanoparticle synthesis and optimized sintering process, can be applied to prepare superior thermoelectric materials.
Co-reporter:Lili Zhao, Lei Miao, Sakae Tanemura, Jianhua Zhou, Lihua Chen, Xiudi Xiao, Gang Xu
Thin Solid Films 2013 Volume 543() pp:157-161
Publication Date(Web):30 September 2013
DOI:10.1016/j.tsf.2012.11.154
This paper describes a solution-based route to synthesize vanadium dioxide (VO2) thermochromic thin films on glass substrate by spin-coating technology followed by nitrogen-annealing with vanadium pentoxide (V2O5) and oxalic acid (H2C2O4) as source material, which is fairly economical and practical. Surface morphologies indicate that the films obtained by this method are homogeneous and particulate, irregular prisms emerge as the annealing temperatures increase. X-ray diffractions show that films annealed at relatively low temperature are pure monoclinic phase with a preferred orientation of (011). NaV4O7 and NaV6O15 form along with raising the heating temperatures. VO2 films obtained exhibit excellent visible transparency and switching property at near-infrared wavelengths across the metal–semiconductor transition. Transmittance change at λ = 2000 nm of VO2 thin film annealed at 450 °C attains as high as 41.5% and its solar modulation efficiency reaches up to 8.8%. The W-doped VO2 film at a doping level of 1 at.% exhibits a thermochromic switch at 37 °C with a narrow hysteresis, which will greatly favor the practical application of VO2-based smart windows.Highlights► Vanadium dioxide thermochromic film was prepared via a solution-based deposition. ► Tungsten doping reduced the phase transition temperature to 37 °C. ► Tungsten doping narrowed the transmittance hysteresis loop. ► Our results will propel the application to vanadium dioxide-based smart windows.
Co-reporter:Lei Miao, Sakae Tanemura, Lili Zhao, Xiudi Xiao, Xiao Ting Zhang
Thin Solid Films 2013 Volume 543() pp:125-129
Publication Date(Web):30 September 2013
DOI:10.1016/j.tsf.2013.02.034
We have reported a low-cost and fast formation of highly efficient Er centers in ZnO thin films. As a high sensitivity tool for the detection of trace of Er dopant in ZnO film, spectroscopic ellipsometry is employed to disclose the systematic interrelationship of the crystallinity, dielectric function and optical band structure. Pure ZnO thin film shows very sharp band structure. The films with 0.05 at.% Er dopant, annealed at 600 °C and 800 °C, exhibit the similar tendency where the dopant level appears at the band tail. The band structure of the films with 0.05 at.% Er dopant, annealed at 400 °C, is very close to that of pure ZnO. While the samples annealed at 1000 °C are on the verge of amorphousness, and the flat curve of photon energy dependent εi(E) is observed. The strain effect caused by the formation of ErO6 pseudo-octahedron structure greatly affects the value of dielectric constants. Therefore, SE analyses reveal significant effect of Er doping and annealing temperatures on the modification of optical band structure, dielectric property and optically active center in ZnO films.Highlights► ZnO:Er films are prepared by a sol–gel spin coating method. ► Complex refractive index and optical band gaps of ZnO:Er films are provided. ► Ellipsometric analyses reveal significant effect of Er light-doping into ZnO.
Co-reporter:Chengyan Liu, Lei Miao, Jianhua Zhou, Rong Huang and Sakae Tanemura
Journal of Materials Chemistry A 2012 vol. 22(Issue 28) pp:14180-14190
Publication Date(Web):21 May 2012
DOI:10.1039/C2JM31469J
Nb-doped TiO2-based nanostructures were novelly prepared by an economical and environmentally friendly hydrothermal method from TiO2 and Nb2O5 powder precursors. The proposed formation mechanism is acceptable for the design of various Nb-doped TiO2-based nanostructures. Furthermore, Nb-doped TiO2 nanostructured bulk materials (nanobulks) embedded with Ag nanoinclusions were first fabricated by the bottom-up assembly of Ag2O nanoparticles loaded Nb-doped TiO2-based nanostructures. The introduction of Ag nanoparticles remarkably increased the Seebeck coefficient (S) of the TiO2 bulk ceramic by 15% to 370 μV K−1 in the maximum case on account of the electron filtering effect. Moreover, their electrical conductivity (σ) was also improved by one order of magnitude up to 160 Ω−1 cm−1, resulting from the contribution of both introducing Ag nanoparticles and Nb-doping. Finally, the figure of merit (ZT) was increased by about two-fold owing to the substantially optimized power factors (S2σ). Our obtained results strongly confirm that the Ag embedded Nb-doped TiO2 nanobulks can be used as good thermoelectric materials up to the high temperature of about 800 °C.
Co-reporter:Xiudi Xiao, Lei Miao, Gang Xu, Limei Lu, Zhanmin Su, Ning Wang, Sakae Tanemura
Applied Surface Science 2011 Volume 257(Issue 24) pp:10729-10736
Publication Date(Web):1 October 2011
DOI:10.1016/j.apsusc.2011.07.088
Abstract
Copper oxide thin films as solar selective absorbers were conveniently prepared by one-step chemical conversion method. X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis–NIR spectra and Fourier transform infrared (FTIR) spectra were employed to characterize the composition, structure and optical properties of thin films. The results indicated that the composition, structure and optical properties of thin films were greatly influenced by reaction temperature, time and concentration of NaOH. When reaction temperature was fixed at 40 °C, the as-prepared films consist of pure cubic Cu2O. The surface morphology of thin films was changed from square-like structure (reaction time ≤ 25 min) to porous belt-like structure (reaction time ≥ 30 min) with the elongation of reaction time. While for thin films prepared at 60 °C and 80 °C, single Cu2O was observed after 5 min reaction. When reaction time is longer than 5 min, CuO appears and the content of CuO is increasing with the elongation of reaction time. With the increase of reaction temperature, the belt-like structure was easily formed for 60 °C/10 min and 80 °C/5 min. Decreasing concentration of NaOH also could result in the formation of CuO and porous belt-like structure. Simultaneously, the film thickness is increasing with the increase of reaction time, temperature and concentration. Films containing CuO with belt-like structure exhibited high absorptance (>0.9), and the emissivity of films increased with elongation of reaction time. Combination of the composition, structure and optical properties, it can be deduced that the porous belt-like structure like as a light trap can greatly enhance absorbance (α), while the composition, thickness and roughness of thin films can greatly influence the emissivity (ɛ). The highest photo-thermal conversion efficiency was up to 0.86 (α/ɛ = 0.94/0.08) for thin films prepared at 80 °C/5 min, which proved that the CuOx thin films can be served as high performance solar selective absorbers.
Co-reporter:L. Miao, S. Tanemura, R. Huang, C.Y. Liu, C.M. Huang and G. Xu
ACS Applied Materials & Interfaces 2010 Volume 2(Issue 8) pp:2355
Publication Date(Web):July 26, 2010
DOI:10.1021/am100365y
Titanate nanotubes Na2−xHxTi3O7 produced by alkali hydrothermally treated ground TiO2 aerogels are investigated as possible materials for high-temperature thermoelectric conversion by measuring their thermoelectric properties. Strikingly, the Seebeck coefficients increased sharply in the temperature range 745 to 1032 K, reaching a maximum of 302 μV/K. The electrical resistivity of the TNNTs ranged from 325 to 525 Ωm, which is lower than that of bulk TiO2, and thermal conductivities at room temperature were also very low, ranging from 0.55 to 0.75 Wm−1 K−1. The hollow structure of the titanate nanotubes, with small, uniform diameters, is thought to be responsible for the ultralow thermal conductivity. The large thermoelectric power and ultralow thermal conductivity suggest that titanate nanotubes represent a new kind of p-type oxide thermoelectric material.Keywords: oxide nanomaterials; Seebeck coefficients; thermoelectric conversion; titanate nanotubes
Co-reporter:Miao Feng, Hongbing Zhan and Lei Miao
ACS Applied Materials & Interfaces 2010 Volume 2(Issue 4) pp:1129
Publication Date(Web):March 23, 2010
DOI:10.1021/am100003p
A facile route to assemble cadmium sulfide (CdS) quantum dots (QDs) uniformly on the surface of titanate nanobelts (TNBs) through electrostatic interactions is demonstrated. The photophysical properties of the resulting TNB-CdS nanostructured composite, including optical limiting properties, were studied using ultraviolet-visible absorption spectroscopy, photoluminescence spectroscopy, and the open aperture Z-scan technique in the nanosecond regime using a laser with a wavelength of 532 nm. The linear and nonlinear optical properties of this composite nanostructure were strongly influenced by a possible charge/energy transfer process between the QDs and TNBs. The as-prepared TNB-CdS composite offers an optical limiting effect that is superior to that of unmodified CdS QDs and TNBs. The main contributors to the enhanced optical limiting effect in the TNB-CdS composite were a combination of nonlinear scattering and increased nonlinear absorption resulting from efficient charge/energy transfer at the CdS/TNB interface.Keywords: composite nanostructure; nanosecond laser; optical limiting; Z-scan
Co-reporter:T. Jiang, L. Miao, S. Tanemura, M. Tanemura, G. Xu, R.P. Wang
Superlattices and Microstructures 2009 Volume 46(1–2) pp:159-165
Publication Date(Web):July–August 2009
DOI:10.1016/j.spmi.2008.10.043
Surface and bulk plasmon resonance of noble metal particles play an essential role in the multicolor photochromism of semiconductor systems containing noble metal particles, Here we examined several key parameters affecting surface plasmon resonance wavelength (SPRW) of Ag particles and investigated the relation between surface plasmon and photochromic reaction wavelength. From the transmission spectra of sandwiched (TiO2/Ag/TiO2) and overcoated (Ag/TiO2) films deposited on quartz substrates at room temperature by rf helicon magnetron sputtering, we demonstrated that the SPRW can be made tunable by changing the surrounding media and thickness of the metal layer. The coloration and bleaching in visible light region due to photochromism were clearly observed for the films inserted with a 0.55 nm Ag layer.
Co-reporter:Ru Chen, Lei Miao, Haoliang Cheng, Eiji Nishibori, Chengyan Liu, Toru Asaka, Yuji Iwamoto, Masaki Takata and Sakae Tanemura
Journal of Materials Chemistry A 2015 - vol. 3(Issue 7) pp:NaN3738-3738
Publication Date(Web):2014/12/19
DOI:10.1039/C4TA05559D
Pure phase V1−xWxO2(M/R) nanorods with superb metal–insulator transition properties were obtained in tungsten (W)-doped level ranges from 0.5 to 2.0 at% using a one-step hydrothermal treatment without additional annealing steps. The assured level of W doping greatly promotes the grain growth of pure phase vanadium oxide (VO2)(M/R) and simultaneously the phase transition temperature (Tc) is depressed as much as 103 °C per at% W for the V1−xWxO2 nanorods when x = 1.0–2.0 at%. After mixing the pure phase VO2(M) (W-doped 0.5 at%, phase transition at 47 °C) nanorods with acrylic resin, the integrated visible transmission of the VO2 composite coating on glass is up to 60.6% and the integrated solar modulation efficiency is up to 10.3%. These results mean that the superior thermochromic property will greatly favor the practical application of VO2-based smart windows.
Co-reporter:Chengyan Liu, Lei Miao, Jianhua Zhou, Rong Huang and Sakae Tanemura
Journal of Materials Chemistry A 2012 - vol. 22(Issue 28) pp:NaN14190-14190
Publication Date(Web):2012/05/21
DOI:10.1039/C2JM31469J
Nb-doped TiO2-based nanostructures were novelly prepared by an economical and environmentally friendly hydrothermal method from TiO2 and Nb2O5 powder precursors. The proposed formation mechanism is acceptable for the design of various Nb-doped TiO2-based nanostructures. Furthermore, Nb-doped TiO2 nanostructured bulk materials (nanobulks) embedded with Ag nanoinclusions were first fabricated by the bottom-up assembly of Ag2O nanoparticles loaded Nb-doped TiO2-based nanostructures. The introduction of Ag nanoparticles remarkably increased the Seebeck coefficient (S) of the TiO2 bulk ceramic by 15% to 370 μV K−1 in the maximum case on account of the electron filtering effect. Moreover, their electrical conductivity (σ) was also improved by one order of magnitude up to 160 Ω−1 cm−1, resulting from the contribution of both introducing Ag nanoparticles and Nb-doping. Finally, the figure of merit (ZT) was increased by about two-fold owing to the substantially optimized power factors (S2σ). Our obtained results strongly confirm that the Ag embedded Nb-doped TiO2 nanobulks can be used as good thermoelectric materials up to the high temperature of about 800 °C.
