HEC／SiO2有机—无机杂化材料的制备与性能

以羟乙基纤维素（HEC）和四甲氧基硅烷（TMOS）为原料，利用溶胶-凝胶技术，通过TMOS在HEC水溶液中的水解-缩聚反应制得了HEC/SiO2凝胶材料。探讨了反应体系pH值、H2O与TMOS的体积比率和HEC用量等因素对HEC/TMOS水解-缩聚体系凝胶时间和光学性能的影响。借助差示扫描量热法考察了HEC/SiO2杂化材料的热性能。并利用扫描电镜观察了HEC凝胶与SiO2凝胶复合前后的微观结构特征。结果表明，随着HEC用量和TMOS浓度的增大，水解-缩聚体系凝胶时间缩短，可见光透过率降低；随pH值的增大，可见光透过率降低，凝胶时间变化较为复杂；HEC/SiO2杂化材料是以HEC凝胶为柔性连续用，SiO2凝胶为刚性分散相的两相体系，该体系热性能较好，玻璃化转变温度为235℃。     

甲基丙烯酸甲酯-顺丁烯二酸酐共聚物/SiO2杂化材料的制备与性能

用γ-氨丙基三乙氧基硅烷(APTEOS)为交联剂，以甲基丙烯酸甲膏(MMA)、顺丁烯二酸酐(MAH)和四乙氧基硅(TEOS)为原料，通过自由基溶液聚合和溶胶-凝胶过程制得了两相间以共价键结合的透明MMA-MAH共聚物／SiO2有机-无机杂化材料。通过FT-IR分析证实了材料有机相与无机相之间是以共价键结合的．随着无机相含量的增加，材料热性能呈明显上升趋势．复合材料可见光透过率在75％左右，当SiO2含量超过一定值后，可见光透过率逐渐降低。研究结果初步表明，在复合材料中有机相和无机相是纳米复合的。     

聚酰亚胺/SiO2杂化薄膜的制备及其透光、隔热性能

以PMDA和ODA为单体原料、DMF为溶剂、TEOS为有机硅源,采用溶胶-凝胶法制备了PI/SiO2杂化薄膜,测试了杂化薄膜的透光率和隔热性能;采用FT-IR、SEM、TG-DTA等分析手段对杂化薄膜的结构、微观形貌及热稳定性进行了表征.结果表明,杂化薄膜的可见光透过率高于85%,紫外光透过率低于10%.隔热性能测试结果显示,杂化薄膜具有良好的隔热性能.结构分析证明,热处理后生成了聚酰亚胺环,形成了有机相-无机相互穿结构.热重分析表明,掺杂SiO2的薄膜失重5%的温度升高了24℃.     

环氧树脂/二氧化硅杂化材料的制备与性能表征

溶胶-凝胶法制备环氧树脂/SiO2杂化材料,利用FTIR、SEM和综合热分析仪对杂化材料的结构、显微形态及热性能进行了表征.结果表明,杂化材料中SiO2与环氧树脂两相间存在氢键作用;SiO2质量分数＜7%时SiO2与环氧树脂之间无明显相界面,可获得有机聚合物链段与无机网络互穿的有机/无机杂化材料;SiO2质量分数为11%时材料具有最佳耐热性能.     

溶胶-凝胶法制备含氟聚丙烯酸酯/SiO2杂化材料的结构与性能

用酸催化溶胶-凝胶法制得SiO2溶胶,与丙烯酸酯单体原位聚合,制备了含氟聚丙烯酸酯/SiO2杂化材料。利用红外光谱、场发射扫描电镜、X射线光电子能谱等表征了杂化材料的结构、形态及表面化学组成;研究了SiO2相的形态、分布和界面状况等与杂化材料的表面性能、热学性能和力学性能的关联与影响。结果表明,SiO2在杂化体系中以Si-O网络的形式存在,并与有机相之间有良好键合;杂化材料的疏水性、热稳定性和硬度随着SiO2含量的增加逐渐增强,附着力则先增大后减小。     

低收缩块状PMMA/SiO_2杂化材料制备及性能表征

以甲基丙烯酸甲酯(MMA)、正硅酸乙酯(TEOS)和硅烷偶联剂(MPMS)为原料,采用溶胶-凝胶法制备出低收缩、具有良好光学性能的PMMA/SiO2杂化材料。通过透射电子显微镜、差热分析、红外吸收光谱和紫外光-可见分光光度计表征了杂化材料的微观形貌、热性能和透明性。结果表明材料的网络结构相对比较均匀,在可见光波长范围内材料均一性好;有机相和无机相之间是通过共价键相互连接的,没有出现有机相、无机相分离现象;杂化材料的透光率约90%。     

共溶剂对溶胶-凝胶法制备PVA/SiO2杂化材料的影响

通过溶胶-凝胶法(Sol-Gel)制得了透明PVA/SiO2杂化材料,重点研究了共溶剂的选择对杂化材料相分离的影响。采用扫描电子显微镜和能谱对使用不同共溶剂制备PVA/SiO2杂化材料体系中产生的沉淀物进行了分析研究。结果表明,在溶胶-凝胶法制备PVA/SiO2杂化材料的PVA-TEOS体系中,在以乙醇、四氢呋喃和乙醛为有机共溶剂的情况下,如果pH值控制不当,溶胶过程中会有絮状沉淀物出现。不使用有机共溶剂可合成具有良好透明性、体积收缩小、没有相分离的PVA/SiO2杂化材料。     

聚醋酸乙烯酯/二氧化硅杂化材料的制备与性能研究

以硅酸钠在HCl溶液中的水解,经四氢呋喃(THF)萃取,制备聚硅酸溶胶,再与聚醋酸乙烯酯(PVAC)的THF溶液混合,经溶胶-凝胶过程制备了PVAC/SiO2有机/无机杂化材料.用扫描电镜(SEM),红外光谱(IR),X射线衍射,热失重及透光率等的分析测试,对制备的PVAC/SiO2杂化材料进行了结构与性能的研究.结果表明:本法制备的杂化材料中SiO2在PVAC的基体中分布均匀,SiO2在非晶态的PVAC中亦呈无定形态,杂化材料的硬度、软化温度和热分解温度都比纯PVAC有较大的提高;SiO2含量少于40%的杂化材料其断裂伸长率、屈服强度和断裂强度也比纯PVAC提高;另外,还发现在制备过程中加入少许偶联剂KH-570后,杂化材料中的有机-无机相间的相容性增加,不易发生相分离,材料的透光性能也大为改善.     

有机-无机分子杂化稀土发光材料研究

利用无机正硅酸乙酯（TEOS）和有机聚乙二醇（PEG），采用溶胶一凝胶法制备了一系列有机／无机纳米杂化复合材料。首先将TEOS在酸性条件下预水解，再与PEG共水解、共缩聚以形成有机／无机杂化网络结构。在溶胶一凝胶过程中引入稀土离子来制备发光材料。通过控制工艺条件得到了具有良好稳定性和发光性能的透明有机／无机纳米杂化材料。     

高折射率ZrO2纳米杂化材料的制备与研究

以4,4’-二羟基二苯硫醚和9,9-二(4-羟苯基)芴，环氧氯丙烷为原料，在碱性条件下缩聚合成一种含S元素含芴结构的环氧树脂基体；通过溶胶-凝胶法，以四正丁醇锆为前驱体，以KH560为偶联剂，在基体上原位合成无机纳米ZrO₂粒子，再经过热固化制备出一种具有高折射率的光学纳米杂化材料。通过红外光谱、¹H核磁共振、X射线衍射、纳米粒度仪等手段对杂化材料的结构进行表征，并采用紫外分光光度仪、热重分析仪、椭圆偏振光谱仪对其性能进行了表征与测试。结果表明：ZrO₂粒子在聚合物基体中合成，并以纳米粒度均匀分散，杂化材料具有很好的光学性能，在可见光范围内普遍保持90%以上的透过率，随着ZrO₂含量的增加，杂化树脂折射率呈线性增加，ZrO₂含量在19.33%时，折射率达到1.739。     

Structural and optical properties of AlxOy/Pt/AlxOy multilayer absorber

We report on the microstructure and optical properties of Al_xO_y–Pt–Al_xO_y interference-type multilayer films, deposited by electron beam (e-beam) deposition onto corning 1737 glass, silicon (1 1 1) and copper substrates. The structural properties were investigated by Rutherford backscattering spectrometry, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and atomic force microscopy. The optical properties were extracted from specular reflection/transmission, diffuse reflectance and emissometer measurements. The stratification of the coatings consists of a semi-transparent middle Pt layer sandwiched between two layers of Al_xO_y. The top and bottom Al_xO_y layers were non-stoichiometric with no crystalline phases present. The Pt layer is in the fcc crystalline phase with a broad size distribution and spheroidal shape in and between the rims of Al_xO_y. The surface roughness of the stack was found to be comparable to the inter-particle distance. The optical calculations confirm a high solar absorptance of ∼0.94 and a low thermal emittance of ∼0.06 for the multilayer stack, which is attributed not only to the optimized nature of the multilayer interference stacks, but also to the specific surface morphology and texture of the coatings. These optical characteristics validate the spectral selectivity of the Al_xO_y–Pt–Al_xO_y interference-type multilayer stack for use in high temperature solar-thermal applications.     

Optimization of AlxOy/Pt/AlxOy multilayer spectrally selective coatings for solar-thermal applications

Spectrally selective Al_xO_y/Pt/Al_xO_y multilayer absorber coatings were deposited onto corning 1737 glass, Si (111) and copper substrates using electron beam (e-beam) vacuum evaporator at room temperature. The employment of ellipsometric measurements and optical simulation was proposed as an effective method to optimize and deposit multilayer solar absorber coatings. The optical constants (n and k) measured using spectroscopic ellipsometry, showed that both Al_xO_y layers, which used in the coatings, were dielectric in nature and the Pt layer was semi-transparent. The optimized multilayer coatings exhibited high solar absorptance α ∼ 0.94 ± 0.01 and low thermal emittance ? ∼ 0.06 ± 0.01 at 82 °C. The Rutherford backscattering spectroscopy (RBS) data of Al_xO_y/Pt/Al_xO_y multilayer absorber indicated the Al_xO_y layers present in the coating were nearly stoichiometry. The scanning electron microscope analysis (SEM) result indicated that the average diameter and inter-particles distance of Pt grains were statistically about 146 ± 0.17 nm and 6-10 ± 0.2 nm respectively.     

Anomalous Hall Effect in Sn1?x?yMnxEuyTe and Sn1?x?yMnxEryTe Mixed Crystals

The Anomalous Hall Effect (AHE) was investigated in IV–VI ferromagnetic semimagnetic semiconductors of Sn_1–x Mn _x Te codoped with either Eu or Er. The analysis of experimental data is as follows. Hall resistivity and magnetization showed that AHE coefficient R _s depends on temperature and its value decreases with thetemperature increase. We observe that above ferromagnet–paramagnet transition temperature R _s changes sign. We discuss the possible physical mechanisms responsible for observed temperature dependence of R _s , particularly change of the sign.     

Synthesis of a new perovskite Pb(Li14Nb34)O3

A high-pressure technique was adopted to obtain perovskite-type $\text{Pb(Li}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{Nb}{}_{\mathrm{<mtext>3</mtext><mtext>4</mtext>}}\text{)}\text{O}{}_3$. A new perovskite $\text{Pb(Li}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{Nb}{}_{\mathrm{<mtext>3</mtext><mtext>4</mtext>}}\text{)}\text{O}{}_3$ was characterized to have a cubic symmetry with $\text{a}{}_{\mathrm{<mtext>o</mtext>}}\text{= 4.069}\text{A}\text{?}$; Li and Nb ions in the B-site of perovskite lattice may be in a random arrangement.     

Bulk crystalline BaPb34Bi14O3: A ceramic superconductor

The preparation conditions of the high T_C ceramic superconductor Ba(Pb,Bi)O₃ is correlated with the superconducting transition. Transition onsets of all materials are similar, but transition widths and transition completeness is strongly dependent on firing temperature. Only materials prepared over a narrow temperature range, resulting in a nearly ideal weight loss, have a complete and narrow transition.     

Interfacial microstructure of NiSix/HfO2/SiOx/Si gate stacks

Integration of NiSi_x based fully silicided metal gates with HfO₂ high-k gate dielectrics offers promise for further scaling of complementary metal-oxide- semiconductor devices. A combination of high resolution transmission electron microscopy and small probe electron energy loss spectroscopy (EELS) and energy dispersive X-ray analysis has been applied to study interfacial reactions in the undoped gate stack. NiSi was found to be polycrystalline with the grain size decreasing from top to bottom of NiSi_x film. Ni content varies near the NiSi/HfO_x interface whereby both Ni-rich and monosilicide phases were observed. Spatially non-uniform distribution of oxygen along NiSi_x/HfO₂ interface was observed by dark field Scanning Transmission Electron Microscopy and EELS. Interfacial roughness of NiSi_x/HfO_x was found higher than that of poly-Si/HfO₂, likely due to compositional non-uniformity of NiSi_x. No intermixing between Hf, Ni and Si beyond interfacial roughness was observed.     

Tc trend in high-Tc superconductors

In our previous works, we have shown that most existing ceramic superconductors can be considered to be built of superconductor-semiconductor composite and we have estimated the change in phonon spectrum of the intrinsic superconductor unit if a semiconductor unit is attached to it. Moreover, the proximity effect under the size quantization condition has been examined in the superconductor-semiconductor composite. Each of the stated effects by itself could causeT _c enhancement in general as more semiconductor blocks are added to the system. We extend our study in this paper to analyze the combined actions of phonon spectral change and proximity effect without size quantization condition onT _c variation in members of the Tl₁ series of high-T _c superconductors. Our results indicate that an optimumT _c is obtained if the stated effects are included in the idealized unit cells of the superconductors made up of a superconductor-semiconductor array.     

Electrostriction in Pb (Zn13Nb23)O3

The electrostriction in $\text{Pb (Zn}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{Nb}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{)}\text{O}{}_3$ crystals has been investigated using a strain gauge method. In the ferroelectric phase below 140 C, the strain vs the electric field shows a hysteresis, which is ascribed to the effect of ferroelectric domains. A quadratic relation holds between the strain x and the electric polarization P as x = QP² above about 170 C in the paraelectric phase. Values of the electrostrictive Q coefficients are determined from the measurements near 190 C, as Q₁₁ = 1.6·10^?2m⁴/C², Q₁₂ = ?0.86·10^?2m⁴/C², and Q₄₄ = 0.85·10^?2m⁴/C².     

Magnetic,electrical and thermal studies on the V1−xMox02

The monoclinic-to-tetragonal structure transition of oxides V_1?xMo_x0₂ with $\text{0≤}\text{x}\text{≤0.20}$ has been studied by means of DTA, X-ray diffraction, magnetic susceptibility (powder samples) and electrical conductivity (single crystals) measurements within the temperature region 80 K to 400 K. A linear decrease of the transition temperature of 11 K per atom % Mo was observed. The magnetic susceptibility of the low temperature phase was found to be temperature independent paramagnetic for all preparations. Electrical conductivity measurements on the same phase showed crystals with $\text{x}\text{? 0.04}$ to be semiconducting, while a metallic behavior was observed in the region $\text{0.10 ?}\text{x}\text{? 0.14}$.