Enhancement of the thermoelectric performance of bulk SnTe alloys via the synergistic effect of band structure modification and chemical bond softening

Wang, Hongchao,Hwang, Junphil,Zhang, Chao,Wang, Teng,Su, Wenbin,Kim, Hoon,Kim, Jungwon,Zhai, Jinze,Wang, Xue,Park, Hwanjoo,Kim, Woochul,Wang, Chunlei Royal Society of Chemistry 2017 Journal of Materials Chemistry A Vol.5 No.27

<P>SnTe alloys, which have the same crystal structure as PbTe, have attracted increasing attention. Here, we demonstrate that the synergistic effect of band structure modification and chemical bond softening can be realized simultaneously in In & Mn doped SnTe bulk alloys. The Seebeck coefficient and power factor are synergistically improved by co-doping of In and Mn. In doping is known to introduce a resonance level. Mn doping reduces the separation of light- and heavy-valence bands. The combination of these effects significantly enhances the Seebeck coefficient at room temperature owing to around a factor of five times increase in the band effective mass. The reduction of thermal conductivity is from the decrease of both the electronic and phononic parts. The electronic thermal conductivity is decreased by the increase in defect scattering, as can be confirmed by the carrier mobility. The force constant of the bonds around the Te site is decreased due to the co-doping of In & Mn, which indicates that the chemical bonds are softened, which leads to low sound velocity and lower lattice thermal conductivity. As a result, the peak thermoelectric figure of merit,<I>zT</I>= 1.03 has been achieved for Sn0.89In0.01Mn0.1Te at 923 K. This strategy of using the synergistic effect of band structure modification and chemical bond softening could be applicable to other thermoelectric materials.</P>

Research on Temperature Points Selection of the Non-source Temperature Calibration Method Based on Pyrometer Transfer Function

Sun Kun,Wang Jing,Wang Hongchao,Yu Limei,Li Chenyang,Zhang Xiaowen 보안공학연구지원센터 2014 International Journal of Control and Automation Vol.7 No.11

The non-source temperature calibration method of the multi-spectral pyrometer (MSP), put forward in the previous article, is the non-source calibration method based on the MSP transfer function (NCCTF). In this paper, the practicability of NCCTF is researched. The situations that maybe encountered of the temperature points in the actual calibration process are simulated. The impact of the intervals temperature points of different number and unequal intervals temperature points on the NCCTF accuracy are researched theoretically to determine the temperature points select method. Simulation experimental results show that the NCCTF can meet the actual calibration process with good usability.

High Thermoelectric Performance of a Heterogeneous PbTe Nanocomposite

Wang, Hongchao,Hwang, Junphil,Snedaker, Matthew Loren,Kim, Il-ho,Kang, Chanyoung,Kim, Jungwon,Stucky, Galen D.,Bowers, John,Kim, Woochul American Chemical Society 2015 Chemistry of materials Vol.27 No.3

<P>In this paper, we propose a heterogeneous material for bulk thermoelectrics. By varying the quenching time of Na doped PbTe, followed by hot pressing, we synthesized heterogeneous nanocomposites, a mixture of nanodot nanocomposites and nanograined nanocomposites. It is well-known that by putting excess amounts of Na (i.e., exceeding the solubility limit) into PbTe, nanodots with sizes as small as a few nanometers can be formed. Nanograined regions with an average grain size of ca. 10 nm are observed only in materials synthesized with an extremely low quenching rate, which was achieved by using a quenching media of iced salt water and cold water. Dimensionless thermoelectric figures of merit, <I>zT</I>, of those heterogeneous nanocomposites exhibited a <I>zT</I> around 2.0 at 773 K, which is a 25% increase compared to <I>zT</I> of a homogeneous nanodot nanocomposite with the largest quenching time in our experiment, i.e. furnace cooled. The power factor increase is 5%, and the thermal conductivity reduction is 15%; thus, <I>zT</I> increase mainly comes from the thermal conductivity reduction.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2015/cmatex.2015.27.issue-3/cm5042138/production/images/medium/cm-2014-042138_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/cm5042138'>ACS Electronic Supporting Info</A></P>

Diagnosis of rolling element bearing based on multifractal detrended fluctuation analyses and continuous hidden markov model

Hongchao Wang,Zhiqiang Guo,Wenliao Du 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.8

The conventional signal processing based methods are difficult to achieve satisfactory results for rolling element bearings (REBs)’ weak fault due to the serious influence of interference signal. Intelligent classification technology and the arising popular monitoring technology-performance evaluation assessment (PDA) are the research hotspots of fault diagnosis of REB in recent years, which could resolve the above problem to some extent. Especially the latter could reflect the operating status of the equipment more comprehensively. Effective feature extraction basing on signal processing methods and intelligent algorithm are the two key aspects for the above two technologies which will determine their effectiveness to great extent. Multifractal detrended fluctuation analyses (MDFA) is an effective non-stationary signal processing method which could reveal the multifractality buried in nonlinear and nonstationary vibration signals of REB, and continuous hidden markov model (CHMM) is a mature intelligent algorithm with solid theoretical basis and rich mathematical structure. So a diagnosis method basing on combination of MDFA with CHMM is proposed in the paper, and it could deal with both fault classification and PDA tasks for the diagnosis of REBs. Effectiveness of the proposed method is validated by two different diagnosis experiments, one for fault classification and another for lifecycle performance evaluation of REBs. Compared to state-of-the-art peer methods, the proposed method has the best performance when dealing with fault diagnosis tasks for REBs.

Experimental Study on Mechanical Properties of Q690 High Strength Steel in Marine Corrosive Environment

Hongchao Guo,Tianqi Lei,Jinguang Yu,Defa Wang,Xiaolei Li 한국강구조학회 2021 International Journal of Steel Structures Vol.21 No.2

In order to study the mechanical property degradation rule of Q690 high-strength steel in the ocean wave splash area, the rusted specimen is obtained by indoor damp heat surrounding soaking environment corrosion test. The scanning electron microscopy, uniaxial tensile and cyclic loading tests of corroded steel are performed. This paper analyzes the steel from elastic modulus, yield strength, ductility and law of hysteresis degradation under diff erent corrosion cycles and establishes the constitutive model of HSS. The results show that the appearance of HSS is obviously aff ected by the corrosion cycle. With the increase of the corrosion cycle, reddish-brown fl aky corrosion products are formed on the surface of the steel and there are obvious corrosion pits. After 100 days of corrosion, the corrosion rate of steel reached 7.21%; the elastic modulus and yield strength under uniaxial tension load decreased by 10.2% and 4.9%. Under the eff ect of cyclic reciprocating load, the hysteretic energy is reduced by 15.3%; at the same time, the test curve is fi tted by the secondary plastic fl ow model and the Ramberg–Osgood model and it is found that the shape parameter S 1 and the cyclic strengthening coeffi cient K’ are reduced by 20.1% and 10.2%, While the shape parameter S 2 and the cycle strengthening index n’ have no obvious changes.

A Novel High Performance SOI LDMOS with Buried Stepped Gate Field Plate

Hongchao Hu,Hongli Dai,Luoxin Wang,Haitao Lyu,Yuming Xue,Tu Qian 한국전기전자재료학회 2023 Transactions on Electrical and Electronic Material Vol.24 No.6

With the continuous development of science and technology, the power semiconductor devices are becoming more and more extensive. A novel silicon-on-insulator (SOI) lateral double-diffused metal–oxide–semiconductor (LDMOS) has been proposed in this paper. The new device is mainly characterized by introducing a stepped gate field plate in the low-K dielectric buried layer (SGFP-LK). On the one hand, the stepped gate field plate introduces extra lateral electric field peaks, which makes the distribution of potential lines more uniform and improves the breakdown voltage (BV). Moreover, the stepped gate fi eld plate decreases the specific on-resistance ( R on,sp ) by a promoted depletion. On the other hand, different from the traditional buried oxygen layer, the low-K dielectric layer strengthens the vertical electric field and signifi cantly increases BV. Ultimately, compared with the conventional device (C-SOI LDMOS), the BV of the SGFP-LK LDMOS is dramatically enhanced by 107% and the R on,sp is reduced by 24.8%. Furthermore, the figure of merit is enhanced by 472%. In addition, the maximum lattice temperature of the SGFP-LK LDMOS is dropped by 23.1 K, which relieves self-heating effects to some extent.

Experimental study on U-shape flat thermosyphon for thermal management of power battery

Tao Wang,Sicong Tan,Cong Guo,Hongchao Su,Chaohong Guo,Yuyan Jiang 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.9

The paper presents a new type of U-shape flat thermosyphon. The thermosyphon has several unique properties relative to general heat pipe such as compact and simple structure (no wick structure), easily to filling the coolant and flexible plate structure and so on. These properties make it an ideal heat transfer device for battery pack thermal management. In this paper, we experimentally study the thermal management performance of the U-shape flat thermosyphon for a battery module. The temperature of the battery module can be controlled below 50 °C under 1.5 C charge rate (300 W), and below 37 °C under 1 C charge rate (120 W), and the corresponding maximum temperature difference is 3 °C and 7 °C, respectively. And higher power generation is helpful to start-up the U-shape flat thermosyphonand maintain a small temperature difference between different battery cells. The performance of the U-shape flat thermosyphonis evaluated using a thermal resistance network model, which showed that there is uneven distribution of heat transfer in the two side of the heat pipe.

A two-step blind source extraction method and its application in fault diagnosis of rolling element bearing

YanQiu Xiao,Hongchao Wang 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.3

The vibration signals will take on cyclical characteristics when fault arises in the rolling element bearing, and a two-step blind source extraction (BSE) method for fault diagnosis of rolling element bearing is proposed in the paper using the above property. Firstly, calculate the theoretical basic cyclet of the target source fault signal, and the weighted separation matrixand desired source signal are obtained coarsely. Secondly, useas the initial weighted matrix and apply the fixed-point algorithm basing on high-order statistics on the observed signals, and much more perfect target source signal is got at last. The proposed method has the following advantages over other BSE method such as constrained independent component analysis (CICA) basing on the analyzed results of simulation and experiment: The fundamental period t of the target source signal does not needed to be estimated accurately, and the reference signal also does not need to be constructed precisely. However, these two conditions are the necessary prerequisites of CICA. Besides, the proposed method also has the advantage of higher accuracy over the other recent BSE methods through comparison.

Valley magnetoelectricity in single-layer MoS₂

Lee, Jieun,Wang, Zefang,Xie, Hongchao,Mak, Kin Fai,Shan, Jie Nature Publishing Group 2017 NATURE MATERIALS Vol.16 No.9

The magnetoelectric (ME) effect, the phenomenon of inducing magnetization by application of an electric field or vice versa, holds great promise for magnetic sensing and switching applications. Studies of the ME effect have so far focused on the control of the electron spin degree of freedom (DOF) in materials such as multiferroics and conventional semiconductors. Here, we report a new form of the ME effect based on the valley DOF in two-dimensional Dirac materials. By breaking the three-fold rotational symmetry in single-layer MoS<SUB> 2</SUB> via a uniaxial stress, we have demonstrated the pure electrical generation of valley magnetization in this material, and its direct imaging by Kerr rotation microscopy. The observed out-of-plane magnetization is independent of in-plane magnetic field, linearly proportional to the in-plane current density, and optimized when the current is orthogonal to the strain-induced piezoelectric field. These results are fully consistent with a theoretical model of valley magnetoelectricity driven by Berry curvature effects. Furthermore, the effect persists at room temperature, opening possibilities for practical valleytronic devices.

Peripheral Insulin Doesn't Alter Appetite of Broiler Chicks

Liu, Lei,Xu, Shaohua,Wang, Xiaojuan,Jiao, Hongchao,Lin, Hai Asian Australasian Association of Animal Productio 2016 Animal Bioscience Vol.29 No.9

An experiment was conducted to investigate the effect of peripheral insulin treatment on appetite in chicks. Six-d-age chicks with ad libitum feeding or fasting for 3 h before injection received a subcutaneous injection of 0, 1, 3, 5, 10, or 20 IU of insulin or vehicle (saline). The results showed peripheral insulin treatment (1 to 20 IU) did not alter significantly the feed intake in chicks under either ad libitum feeding or fasting conditions within 4 h (p>0.05). Compared with the control, plasma glucose concentration was significantly decreased after insulin treatment of 3, 5, 10, and 20 IU for 4 h in chicks with ad libitum feeding (p<0.05). In fasted chicks, 10 and 20 IU insulin treatments significantly decreased the plasma glucose level for 4 h (p<0.05). Peripheral insulin treatment of 10 IU for 2 or 4 h did not significantly affect the hypothalamic genes expression of neuropeptide Y, proopiomelanocortin, corticotropin-releasing factor and insulin receptors (p>0.05). All results suggest peripheral administration of insulin has no effect on appetite in chicks.