掺镁近化学计量比LiTaO3晶体的生长及光学性能

在同成分LiTaO3熔体中掺入一定剂量的K2O,采用顶部籽晶提拉法生长掺镁近化学计量比LiTaO3晶体.对晶体分别进行光谱分析,畴结构和抗光损伤阈值的测定.结果表明:与同成分掺镁LiTaO3晶体相比较,其紫外吸收边出现明显蓝移,红外吸收峰变弱.腐蚀晶片的晶相显微镜观察结果表明:掺镁近化学剂量比晶体的畴结构是较为规则的六边形;晶体的抗光致散射能力明显提高.     

ZrO2的电学性质与缺陷结构

应用缺陷化学理论，探讨了纯ＺｒＯ２晶体的缺陷结构和电学性质，以及添加稳定剂对ＺｒＯ２电学性质的影响，解释了ＺｒＯ２用作导电陶瓷的某些特性。     

一种有机-无机杂化冠醚型超分子化合物的合成、晶体结构和介电性质

4-溴苯胺、18-冠醚-6、高碘酸以一定的配比反应,成功合成了一种新型的超分子化合物(4-BrC6H4NH3)+(18-crown-6)(IO4)-,并通过X-射线单晶衍射、红外光谱(IR)、粉末XRD、热重分析(TG)、变温介电测试等对其进行表征。单晶结构解析表明:低温(128 K)和室温(296 K)时,化合物空间群为Pnma,均为正交晶系。4-溴苯胺分子中的溴原子与相邻的—NH3+基团形成N—H…Br氢键,穿过18-冠醚-6分子的空腔,在b轴方向形成一维氢键链状结构。在100～310 K、500 Hz～1 MHz范围内对晶体的介电性能进行测试,在223 K附近出现明显的介电响应。     

FOX-7晶体的制备和热性质

为了解FOX-7晶体形状和尺寸对其热性质的影响,通过冷却结晶和阻溶剂结晶的方法从DMF/H2O、NMP/H2O体系中获得FOX-7晶体.SEM结果表明,得到的晶体基本为延长的四面或六面棱柱和斜方菱晶两种类型,不同溶剂体系中得到晶体的尺寸不同和包含的颗粒数量也不同,超声处理得到的晶体具有单一形状,只是其表面较粗糙.DSC测试结果表明,不同结晶方式和不同溶剂体系中获得的FOX-7晶体的热性质有一定的差别.由此得出,不同的结晶方式和溶剂体系可以获得不同形状、尺寸和热性质的FOX-7晶体,而超声处理可以很好地控制晶体的形状.     

Zn∶LiTaO_3的结构及其光学性能的研究

本文采用提拉法生长Zn(3(mol)%,5(mol)%,7(mol)%):LiTaO3晶体.通过Zn:LiTaO3晶体的紫外-吸收光谱和红外光谱测试结果来推测Zn2+对晶体结构的影响.ZnO掺杂3(mol)%,5(mol)%时,Zn2+取代反位钽的位置,从而使晶体中的光电导下降,晶体的抗光损伤性能得到改善.当ZnO掺杂达到7(mol)%时,Zn2+将晶体中的所有反位钽取代,并开始取代正常晶格的Li位,因此,晶体的抗光折变性能比纯的钽酸锂晶体提高了两个数量级.     

Al2O3基陶瓷复合材料中LiTaO3颗粒内的电畴结构

采用TEM技术对Al2O3基陶瓷复合材料中LiTaO3颗粒内的电畴结构进行了研究。结果表明:LiTaO3单晶中不可能形成的90°畴出现在LiTaO3/Al2O3(简称LTA)陶瓷复合材料中的LiTaO3晶粒内,且以其为主,这对于六方结构的LiaO3来说,是一个新的发现。采用不同烧结方法制备的LTA陶瓷复合材料中LiTaO3晶粒内的电畴结构有很大差别。1500℃热压烧结,LTA陶瓷复合材料中LiTaO3晶粒内的电畴结构主要为高密度的薄片状90°畴以及箭尾型90°畴;200 MPa冷等静压成型后经1300℃无压烧结,LTA中LiTaO3晶粒内除了薄片状与箭尾型的90°畴结构外,还形成了尖劈状与板条状的90°畴结构;1 300℃热压烧结,LTA中LiTaO3晶粒内的电畴结构大多为板条状的90°畴,另外还有少量尖劈状的90°畴。LiTaO3晶粒内部电畴结构的不同与LiTaO3晶粒受周围Al2O3基体晶粒的应力作用、LiTaO3的化学组成配比以及薄膜试样制备过程中的机械研磨抛光有关。     

晶粒状态对LiTaO3电畴结构的影响

通过TEM技术研究了Al2O3/LiTaO3陶瓷复合材料中LiTaO3颗粒内的电畴结构,并将LiTaO3单晶、LiTaO3作为基体和LiTaO3作为第二相时其晶粒内的电畴结构进行比较。观察表明:纯LiTaO3陶瓷内的电畴结构基本上为曲流状180°电畴,也有非常少量的非180°电畴;15ALT陶瓷复合材料可看出LiTaO3晶粒内非180°电畴明显增多,且板条状与尖劈状两种状态都存在,但其中曲流状180°电畴明显可见;30ALT陶瓷复合材料中,只有少量的曲流状180°电畴,其中非180°电畴是这几个组分中数量最多、分布最密集的。LiTaO3晶粒内部电畴的形成与周围颗粒对其约束产生的应力有关。     

基于量化计算方法预测钼Mo的热力学性质分析

Mo是一种应用非常广泛的金属,但由于其高熔点和高沸点,通过实验的方法获得其某些可靠的热力学参数有一定的困难。本文采用量化计算方法,对Mo晶体进行结构优化,并对优化后的晶体,进行分析计算,得到了声子散射、能态密度等数据。在准谐性近似下,进一步计算晶体的焓、熵、自由能,并且可以得到德拜温度与温度的关系,模拟结果如下:Final energy为-220.0793 eV,Final free energy为-220.0859 eV,高温极限的Debye温度为380K。为进一步研究,开发Mo提供基本物性参数。     

滑石质日用细瓷的显微结构及性质

叙述了日用滑石瓷结构中的各种物相比例，主晶相类型、粒径大小及其分布状态、性质，个绍了其具有晶体小、结构细微、光学性质相似，具有同质异构体的独特显微结构，探讨了显微结构与生产工艺、各项性能的相互依赖关系。     

NH3和PH3的性质比数

本文应用等电子体原理，以氨（NH3）和磷（PH3）为例，说明互为等电子体的物质，结构相似，性质也必然相似这一普遍规律。同时，由于结构和热力学原理等因素的影响，使NH3和PH3在性质上又有明显的差异。     

压电陶瓷颗粒对结构陶瓷力学性能影响规律及机理的初步探讨

通过对压电、结构陶瓷粉末的选择搭配烧结，发现压电相LiTaO3与基体Al2O3在烧结时能稳定共存，分别采用三种烧结路线制备了LiTaO3/Al2O3陶瓷复合材料，对其微观组织与力学性能进行了研究，结果表明，LiTaO3晶粒中的电畴结构清晰可见，采用适当的烧结路线制备的含有适量压电陶瓷颗粒陶瓷基复合材料的力学性能显著改善，电畴运动引起的能量耗散是一种新的结构陶瓷增韧机制。     

DC conductivity and AC impedance of Mn doped magnesia alumina spinel (MgAl2-2xMn2xO4) over a large temperature range

MgAl_2-2xMn_2xO₄ (MAMO) with x = 0-0.12 was synthesized in a single-phase form by solid-state reaction. XRD analysis showed that the samples had the cubic center structure of the Fd-3 m space group. Electrical properties of the samples were studied over the temperature range of 300 K∼1073 K. The results showed that the DC conductivity (σ_DC) increased from 10⁻¹¹S/cm at 300 K (MAMO, x = 0) to 10^-3S/cm at 1073 K (MAMO, x = 0.12). The equivalent circuit of the complex impedance spectra suggested that the relaxation of charge carriers was of non-Debye type. The conduction was mainly caused by grain boundaries and the capacitance was mainly attributed to polarization. The complex permittivity values (ε’ and ε’’) were increased by two orders of magnitude with the increase in Mn content and temperature over the measured frequency range (1 Hz-1 MHz). Therefore, doping with Mn could be applied to modify the electrical properties of MAMO at high temperature.     

热处理对木质纤维素Iβ结构及其力学性能影响的分子动力学模拟

采用分子动力学模拟方法对木材主要成分纤维素I_β在热处理环境下的结构和力学性能进行研究,建立了用于模拟的3×3×3纤维素超胞模型,得到350~550 K的体积、密度及氢键变化图,分析了纤维素微观结构的变化并计算了其力学性能。结果表明：升温过程中晶胞体积逐渐增大,由350 K的11.99 nm³增加至550 K的12.26 nm³,模型密度为1.581~1.617 g/cm³,与实验结果一致。氢键数量总数减小了24%,分子链内氢键部分断裂而形成了新的链间氢键,链内氢键与链间氢键的比值由2.1：1变成1：1.5,进而影响了其力学性能。随着温度的升高,杨氏模量逐渐降低,变化率约为13%。相比于杨氏模量,剪切模量和体积模量受温度影响较小,没有明显的变化趋势。     

Ba(Zr_(0.055)Ti_(0.945))O_3含量对[(Na_(0.80)K_(0.16)Li_(0.04))_(0.5)Bi_(0.5)]TiO_3陶瓷性能的影响

系统研究(1-y)[(Na0.80K0.16Li0.04)0.5Bi0.5]TiO3-yBa(Zr0.055Ti0.945)O3无铅压电陶瓷,获得压电应变常数高达185pC/N的0.94[(Na0.80K0.16Li0.04)0.5Bi0.5]-TiO3-0.06Ba(Zr0.055Ti0.945)O3压电陶瓷。样品的晶体结构为三方相、四方相共存,处于准同型相界(morphotropic phase boundary,MPB)附近。该类陶瓷室温MPB的摩尔(下同)含量为0.050y0.065。样品y=0.060在40°左右的(003)、(021)双峰与46.5°左右的(002)、(200)双峰分裂最明显。随着Ba(Zr0.055Ti0.945)O3含量的增加,铁电相-反铁电相相变温度(θd)升高、反铁电相-顺电相相变温度(θm)降低;θd和θm的温差越来越小,材料的弛豫性逐渐降低。     

Quantification of relaxor behavior in (1 − x)Na0.5Bi0.5TiO3 – xCaTiO3 lead-free ceramics system

This work examines the relaxor behavior of lead-free ceramic (1 − x)Na_0.5Bi_0.5TiO₃–xCaTiO₃ systems. A stable rhombohedral (R3c) phase is detected at room temperature for all compositions by XRD and Raman spectroscopy. Relaxor behavior was observed in the temperature range 300 K - 400 K for all materials. Ceramics exhibit normal ferroelectric properties at room temperature, and then they develop relaxor characteristics with increasing temperature showing the same dispersive properties. This work quantifies the relaxor phenomenon at low temperature. For instance, the maximum temperature of relaxor and the order of dispersion were determined at the strongest dispersion. Finally, the substitution by low CT concentration unaltered the relaxor behavior at low temperature.     

Studies on characterization and cryogenic mechanical properties of polyimide-layered silicate nanocomposite films

Polyimide/layered silicate nanocomposites were prepared via in situ polymerization process from PMDA-ODA and organo-MMT in a solution of N,N-dimethylacetamide. XRD, FTIR, UV-vis analyses showed that at the content of 1 wt% MMT, MMT were well intercalated, exfoliated and dispersed in polyimide matrix. As the MMT content is more than 3 wt%, MMT agglomerates became severe as shown by the transparency and transmittance of the hybrid films. The cryogenic mechanical properties of the films at 77 K were studied and compared with those at room temperature. The cryogenic tensile strength showed the highest value at 1 wt% MMT content, and its strength, modulus and elongation at break were simultaneously increased than the pure PI film. The cryogenic elastic modulus exhibited an increasing trend until the MMT content reached 10 wt%. The cryogenic failure strain of hybrid films with 1-3 wt% MMT contents was greater than 10%, showing good ductility at 77 K. The tensile strength and modulus of the hybrid films at 77 K were generally higher than those at room temperature except at 20 wt% MMT for the strength.     

热处理温度对炭纤维结构和性能的影响

在不同温度下对3K聚丙烯腈基炭纤维进行了高温处理，研究了热处理温度对炭纤维结构和性能的影响。试验结果表明，随着热处理温度的提高，炭纤维线密度下降，微晶层间距缩小，碳含量、微晶尺寸和拉伸模量得以提高。高温处理导致炭纤维拉伸强度发生较大损失，在本次试验中，在不同的热处理温度下，纤维强度下降的程度不同。     

Al2O3/LiTaO3陶瓷复合材料的制备与力学性能

采用氮气保护热压烧结工艺制备Al2O3/LiTaO3(简称ALT)陶瓷复合材料，系统研究了其微观组织和力学性能。ALT陶瓷复合材料的相对密度比烧结纯LiTaO3陶瓷的高得多，表明Al2O3起到烧结助剂的作用。TEM观察表明，Al2O3p分布均匀，两者结合紧密，界面上有非常微量的分解物。ALT陶瓷复合材料的力学性能均随Al2O3p含量的增加而提高，Al2O3p的体积分数为40％时，其各项力学性能都是最高。     

Thermal and electrical properties of a high entropy carbide (Ta,Hf, Nb,Zr) at elevated temperatures

The thermal and electrical properties were measured for a high entropy carbide ceramic, consisting of (Hf, Ta, Zr, Nb)C. The ceramic was produced by spark plasma sintering a mixture of the monocarbides and had a relative density of more than 97.6%. The resulting ceramic was chemically homogeneous as a single-phase solid solution formed from the constituent carbides. The thermal diffusivity (0.045–0.087 cm²/s) and heat capacity (0.23–0.44 J/g•K) were measured from room temperature up to 2000°C. The thermal conductivity increased from 10.7 W/m•K at room temperature to 39.9 W/m•K at 2000°C. The phonon and electron contributions to the thermal conductivity were investigated, which showed that the increase in thermal conductivity was predominantly due to the electron contribution, while the phonon contribution was independent of temperature. The electrical resistivity increased from 80.9 μΩ•cm at room temperature to 114.1 μΩ•cm at 800°C.