CURRENT RESEARCH INTERESTS
1. Vanadium Di-Oxide (VO2)-Based Smart Window
Smart window for energy saving is a type of window that can change its optical performance under external stimulus (electricity, light, gas, etc.) to regulate solar energy transmittance to reduce building energy consumption. VO2-based smart window is a kind of thermochromic smart window that could change its infrared transmittance following the environment temperature change based on the reversible phase transition of VO2 thin films. Specifically, at a low temperature, VO2 is semiconductor, having high transmittance in infrared waveband, while as temperature increased, VO2 turns to metal, and the transmittance of infrared waveband is reduced. This performance endues the window the ability of regulating the solar heat flux by responding to temperature: in hot days, it blocks solar heat, reducing space cooling consumption, and in cold days, it transmits solar heat, saving energy from space heating.
2. Thermal/Environmental Barrier Coatings
High-temperature thermal barrier coatings (TBCs) are mainly applied on the surface of hot section components in high thrust-weight ratio rocket, ships, aircraft engines and gas turbines. The protection of hot section components by TBCs allows higher in-let temperature of gas and more sufficient combustion, which increases the efficiency of gas turbine in working condition. Thus, it helps to save energy and reduce the emission of COx and NOx to the atmosphere. Our research interest includes following areas: (1) the development of new thermal barrier coating powders; (2) the technical procedure of plasma spraying and Laser-CVD, and the growth mechanism of coatings; (3) the reliability evaluation of thermal barrier coatings and exploration of nondestructive detection method.
3. Vanadium Oxide (VOx) Uncooled Focal Plane Arrays (UFPA)
Technology providing for infrared (IR) imaging ability, of which night vision is the most obvious application, is of great current interest. In the past 2 decades this interest was primarily pursued by the military; civilian applications- a spin-off of military developments which were made public in 1992- abound as well. In its prevailing implementation, IR imaging in the atmospheric window 8-14 μm is based on large arrays of microbolometers (105- 106 pixels) placed in a focal plane of IR optics, and operating at room temperature (Uncooled focal plane array (UFPA) technology). Absorbed IR radiation changes the temperature of a microbolometer, which in turn changes its resistance, the latter being read out from each pixel, eventually being converted into a picture in the visible domain.
A large number of infrared UFPA technologies based on silicon IC process and a micromachining technique have been developed in the past several years. Among the thermal sensitive materials, vanadium oxides are more attractive and have been subjected for intensive applications due to its excellent resistance properties, suitable thermal times constanct τ, low 1/f noise, and high temperature coefficient of resistance (TCR).
The researches in our group are focused on the synthesis and applications of the uncooled infrared thermal detecting vanadium oxides thin films. Through novel design of film system and effective microstructural controlling, the performances of the UFPA system are hope to greatly improved and the cost to be controlled.
4. Thermoelectric materials
Thermoelectric materials are a kind of green energy materials which can convert waste heat directly into useful electricity. Considering that about two-thirds of the consumed energy is lost as waste heat, thermoelectric materials show not only distinguished advantage but also promising potential in waste heat harvesting. Thermoelectric performance of a material is determined by its electrical and thermal transport properties. A dimensionless thermoelectric figure of merit ZT, ZT = S2σT/ktot, is introduced to evaluate the thermoelectric properties. S, σ, ktot, and T are the Seebeck coefficient (or thermopower), electrical conductivity, total thermal conductivity, and absolute temperature, respectively. ktot includes contributions from both carriers (ke, electronic thermal conductivity) and phonons (kl, lattice thermal conductivity). According to above formula, ZT can be enhanced by increasing S and σ as well as by decreasing ke and kl. Carrier concentration optimization is usually the first step for the routine way to improve electrical transport properties. With the optimized carrier concentration, σ can be further increased by increasing mobility. Comparing with σ, the increase of S is more desired because of its square relation with ZT. The enhancement of S can be achieved through resonant doping, band engineering, and energy filtering. For the reduction of thermal conductivity, the introduction of crystal defects, grain boundaries, and nanoscale impurities into the matrix is substantially effective, which results in a remarkably enhanced phonon scattering and therefore dramatically reduced lattice thermal conductivity. Currently, our research focuses on designing and synthesizing of new thermoelectric materials, optimizing their thermoelectric performance, and integration of energy saving and power generation.
5. Li-ion Rechargeable Battery (LIB)
The Li-ion rechargeable battery (LIB) consists of inorganic electrolyte with a larger window, a lithium contained cathode and a lithium free anode, which are separated with a separator. During the charging process, Li ions de-intercalate from the cathode and then intercalate into the anode through the electrolyte, meanwhile, the cathode releases electrons via an external circuit to anode, making charge equilibrium. The opposite is true for the discharging process.
The Li-ion rechargeable batteryhas enabled the wireless revolution of cell phones, laptop computers, digital cameras and iPads that have transformed global communication. It is also used in some devices demanding the battery with the large capacity, such as the electric vehicle, intermittent energy sources including the storage of solar energy and the dispatching of smart grid.