Metal-to-insulator transition and its effective manipulation studied from investigations in V1-xNbxO2 bulks

Nb doping effects on crystalline structure, transport transition and magnetic properties are investigated for V_1-xNb_xO₂ (0 $\le$x$\le$ 5%) bulks. At room temperature, doping does not change structure of monoclinic phase but causes an increase in lattice parameters for the range of x$\le$ 3%, further doping leads to a structure transition to rutile tetragonal phase. Each sample simultaneously displays a transition to insulating behavior and a sharp decrease in susceptibility below an almost same critical temperature (T_c). The T_c is shown to shift from ~ 340 K at x = 0 to ~ 277 K at x = 5% at a rate of ~ ?13 K/at%. It is argued that the observed sharp decrease in susceptibility originates from the formation of V-V dimers with spins in anti-parallel, while the insulating behavior below T_c is due to the electron movement from one dimerized state to another with the help of Variable-Range-Hopping mechanism. Furthermore, it is proposed that doping by larger cations, which would suppress the formation of dimers, can be used to manipulate the metal-insulator transition to lower temperatures.     

Low metal–insulator transition temperature of Ni-doped vanadium oxide films

Elemental doping is the main means to regulate the phase transition of vanadium oxide (VO₂); however, the effects of low valence elemental (<4+) doping on the phase transition of VO₂ are still controversial. In the present work, Ni-doped VO₂ films were prepared on quartz glass by direct current reactive magnetron sputtering and subsequent annealing. With the increase of the Ni doping content, the phase transition temperature of heating (T_H) of the VO₂ films decreased from 73.4 °C to 52.4 °C. The temperature required for the occurrence of phase transition (T_b) was lower than T_MIT. Different from the undoped VO₂ film, the Ni-doped VO₂ films had a T_b of around 30 °C. XRD and Raman results revealed that some rutile VO₂ microcrystals appeared in the vanadium oxide films because of the lattice distortion by incorporated Ni. Hence, rutile VO₂ micro-crystallinities significantly facilitated the phase transition of monoclinic VO₂ to rutile one.     

热红外隐身材料的发展状况

简要介绍了红外隐身材料的隐身原理，综述了目前红外隐身材料的种类及研究现状，分析了近年来开始研究的红外—微波复合隐身材料，最后指出了红外隐身材料的发展方向。     

红外隐身涂料研究进展

简单介绍了红外隐身涂料的主要组成，综述了红外隐身涂料的研究及发展现状，提出了红外隐身涂料的发展方向。     

红外隐身材料的研究进展

现代战争中,随着红外探测制导技术的迅猛发展,武器装备的生存环境愈发严峻,如何提高武器装备的红外隐身能力成为亟待解决的问题,而红外隐身材料是提升武器装备红外隐身能力的关键。本文简要分析了红外隐身材料的隐身机理,总结了近年来红外低发射率材料、控温材料、光子晶体、智能隐身材料、红外低发射率纳米材料等红外隐身材料的研究现状,展望了红外隐身材料未来的发展趋势。     

Photoluminescence response of colloidal quantum dots on VO2 film across metal to insulator transition

We have proposed a method to probe metal to insulator transition in VO₂ measuring photoluminescence response of colloidal quantum dots deposited on the VO₂ film. In addition to linear luminescence intensity decrease with temperature that is well known for quantum dots, temperature ranges with enhanced photoluminescence changes have been found during phase transition in the oxide. Corresponding temperature derived from luminescence dependence on temperature closely correlates with that from resistance measurement during heating. The supporting reflectance data point out that photoluminescence response mimics a reflectance change in VO₂ across metal to insulator transition. Time-resolved photoluminescence study did not reveal any significant change of luminescence lifetime of deposited quantum dots under metal to insulator transition. It is a strong argument in favor of the proposed explanation based on the reflectance data.

PACS

71.30. + h; 73.21.La; 78.47.jd     

The effect of particle size on structural,magnetic and transport properties of La0.7Sr0.3MnO3 nanoparticles

This paper reports the synthesis of different particle size La_0.7Sr_0.3MnO₃ (LSMO) nanoparticles using non-aqueous sol gel synthesis route by calcination at temperatures 750 °C, 850 °C and 950 °C. In the present work, the effect of particle size of LSMO nanoparticles on its structural, magnetic and transport properties has been studied in detail. The X-ray diffraction analysis confirms the formation of LSMO nanoparticles having rhombohedral ($R\stackrel{?}{3}c$) structure with average particle size of 20 nm, 22.5 nm and 25.6 nm. An increase in magnetization and decrease in coercivity with increase in particle size is attributed to the magnetically disordered surface layer. The bifurcation in ZFC-FC magnetization indicates the possibility of spin glass like behavior of the LSMO nanoparticles. The effect of particle size on the resistivity and magnetoresistance were studied by using different conduction mechanism for different temperature regions. The upturn in the ρ-T curve at lower temperatures was explained by using Kondo-like transport mechanism. The maximum LFMR achieved was 32.3% at a field of 1 T at 10 K for 20 nm LSMO nanoparticle.     

红外隐身涂料黏合剂的应用与研究

简要介绍了红外隐身涂料的隐身原理;综述了目前红外隐身涂料树脂的种类及研究现状;指出了红外隐身涂料的发展方向。     

热红外伪装涂料的制备研究

以自制的水性粘合剂制备了一种热红外伪装涂料,刷涂于载体上,制得热红外伪装涂层.研究了载体的种类和涂层增质量率对涂层红外发射率的影响,并研究了涂层增质量率对涂层透湿、耐磨和耐有机溶剂等性能的影响.研究结果表明:选用涤纶布为涂层载体,当涂层增质量率为30％时,制备的织物涂层具有良好的透湿性、耐摩擦性和耐有机溶剂腐蚀性,此时涂层的红外发射率为0.61,满足作为热红外伪装织物的基本要求.     

低发射率红外隐身涂料研究进展

简介红外隐身涂料的隐身原理,重点探讨构成低发射率红外隐身涂料的颜料、黏合剂及隐身涂料红外性能的各种因素,结合国内外研究进展状况,对低发射率红外隐身涂料的后续研究提出了基本设想。     

Structure and properties of (1-x)La0.67Sr0.33MnO3/xMnOδ multicomponent composite

(1-x)La_0.67Sr_0.33MnO₃/xMnO_δ [(1-x)LSMO/xMnO_δ] multicomponent composites were prepared. Their structure and properties were investigated as function of composition. X-ray diffraction and x-ray photoelectron spectroscopy confirmed the coexistence of MnO, Mn₂O₃ and MnO₂. It was found that MnO_δ introduction led to decreased average grain size and metal-insulator transition temperature. But it can increase maximum resistivity and magnetoresistance. The corresponding values were 2.0 μm, 370 K, 0.017 Ω cm, −24.7% (10 K, 2 T) for x = 0 and 0.7 μm, 225 K, 1.899 Ω cm and −25.6% (10 K, 2 T) for x = 0.3. However, the ferromagnetic Curie temperature was almost composition-independent with the value of 305 K. These results indicate that forming multicomponent composite by introducing ferromagnetic second phases can suppress the drawbacks of conventional ferromagnetic materials.     

Preparation,dielectric property and infrared emissivity of Fe-doped ZnO powder by coprecipitation method at various reaction time

Fe-doped ZnO powders have been synthesized by the coprecipitation method at 600 °C with various reaction time, using zinc nitrate as the staring material, urea as the precipitator, and ferric nitrate as the doping source, respectively. The phase and morphology of the prepared powders have been characterized by X-ray diffraction and scanning electron microscopy, respectively. It was found that the prepared product synthesized for 1 h had a pure ZnO wurtzite structure and was a ZnO(Fe) solid solution powder. The real part, imaginary part, and dielectric loss of complex permittivity of prepared powders in the frequency range of 8.2–12.4 GHz decreased with increasing reaction time. The average infrared emissivities of prepared powders at the waveband range of 8–14 μm increased with extending reaction time.