制备条件对镥铝石榴石纳米粉体合成的影响

采用溶剂热法研究起始材料硝酸镥(Lu(NO_3)_3·6H_2O)和硝酸铝(Al(NO_3)_3·9H_2O)中结晶水去除前后对镥铝石榴石(LuAG)纳米粉体合成的影响;比较高温热处理对LuAG纳米粉体合成的影响;利用X射线衍射仪、红外光谱仪、透射电子显微镜分析所得粉体的物相组成、微观形貌和分散情况。结果表明,对于含结晶水的起始材料采用溶剂热法能够合成纯相的LuAG纳米粉体,颗粒尺寸为100 nm左右且具有较好的分散性;高温热处理后,纳米粉体结构趋于完整,但纳米颗粒有团聚现象。认为原材料中结晶水的去除不利于溶剂热法合成LuAG纳米粉体,而高温热处理所得的LuAG纳米粉体均已结晶。     

钛酸锶的宽频带介电谱

利用计算机自动控制的超低频介电谱测量装置和HP4192A阻抗分析仪，在10^-4Hz～10^5Hz宽这九个数量级的范围内测量了钛酸锶陶瓷的频域介电谱。其频域复介电常数可很好地拟合为两项之和。其中超低频项来自于晶界间空间电荷运动的贡献，高频项来自于晶粒内部空间电荷运动的贡献。高频项复介电常数的实部在频率增大时变为负值，这说明介电谱用频域方法来描述是有缺陷的，其测量结果无法用传统的介电极化加以解释。     

钽铌酸锂晶体的介电谱研究

研究了钽铌酸锂(LiTa_xNb_(1-x)O_3,x=0,0.02,0.06,0.59,0.92和1.00)晶体在室温的低频和射频介电谱。给出了它们的自由介电常数和受夹介电常数。讨论了低频介电损耗与晶体组分的关系。指出低频介电响应的测量可以作为衡量晶体质量的一种手段。     

SrTiO3基陶瓷的介电谱研究

采用标准的固相反应法制备成０．９１（Ｓｒ０．８４Ｐｂ０．１６）ＴｉＯ３＋０．０９（Ｂｉ２Ｏ３·３ＴｉＯ２）介电陶瓷（缩记为ＳｒＴｉＯ３基陶瓷），并详细地研究了此种陶瓷的介电谱，即介电温度谱和介电频率谱。由介电谱确定了此种陶瓷的结构相变、居里温度、介电弛豫频率和介电弛豫时间，并对它们进行了讨论。     

高温下尼龙11介电谱的研究

研究了尼龙１１在高温下的介电松驰温度谱和频率谱，发现了１个新的超强介电松弛峰－αＨ松弛峰，其松驰强度ΔＥ可达２５３００，松驰活化能ΔＥ为８９．１ｋＧ／ｍｏｌ，αＨ松驰十分符合拜松驰模型，相对介电常数ε′和ε″的柯尔－柯尔图接近于１个半圆，αＨ松驰是由于在高温低频下尼龙１１中不连续氢键形成的缺陷偶极子在电场的作用下产生界面极化而引起的。     

耗尽层的时域介电谱

从金属-半导体-绝缘体-金属（MSIM）层的非线性效应和慢极化效应分析了不能用正弦讯号的频域方法来研究其动态性质的原因．对于这种结构,用时域介电谱方法能更可靠地分出MOS结构的接触层和绝缘层中空间电荷运动的许多重要信息．     

高介电陶瓷材料在油品介电精制方法中的应用

目前对于介电材料的研究与应用一般集中于电子产品及其相关领域，高介电陶瓷材料应用于油品精制领域还是一个新的尝试。首先简要介绍了介电力学精制工艺装置，并重点讨论了介电陶瓷在其中的应用及基本原理，最后选用几种不同介电常数的介电陶瓷材料在装置中进行了实验，实验证明，高介电陶瓷材料对油品有较好的精制效果，并且对于所选用的几种介电材料而言随着介电常数的增加精制效果也提高。     

聚合物材料中的慢极化介电驰豫

用时域方法在低频范围了涤纶，聚丙烯，线性低密度聚乙烯，绝缘纸等聚合物材料的介电谱，结果发现随着温度升高，聚合物的慢极化出现多驰豫机构，而且介电响应函数有别于传统的经验公式。     

稀土掺杂钇铝石榴石晶体激光光纤的研究进展

受激布里渊散射(SBS)和热管理限制了玻璃光纤在光纤激光器中极限输出功率的提高.钇铝石榴石(YAG)晶体光纤结合了晶体和光纤的优点,相较于玻璃光纤,它的SBS增益系数低得多,可以有效地减小非线性效应和热损伤,为光纤激光器研究提供了新的方向.YAG晶体在达到熔点(1970℃)后会迅速熔化成低粘度液体,不利于晶体光纤的制备;制备YAG晶体纤芯/玻璃包层的复合光纤是研究YAG晶体光纤的主要方法,但是存在YAG晶体纤芯玻璃化、纤芯与包层间的成分扩散以及数值孔径过大的问题;未掺杂的YAG晶体作为稀土掺杂的YAG晶体纤芯的包层生长困难,有待于进一步研究.目前多采用激光加热基座生长技术(LHPG)和微下拉法(μ-PD)制备YAG晶体光纤,且制得的光纤质量较好;对YAG晶体光纤的研究,重点在于采用折射率、热膨胀与YAG晶体相匹配的玻璃或晶体作为包层,并探索复合工艺,减小数值孔径和减少纤芯与包层间的扩散,现有文献报道的最大输出功率达到590 W.本文介绍了几种YAG晶体光纤的制备方法,对国内外关于无包层稀土掺杂YAG晶体光纤、玻璃包层稀土掺杂YAG晶体复合光纤、YAG晶体包层晶体光纤及YAG晶体光纤与传统无源光纤器件的熔接的研究现状进行了综述,并对目前的研究状况进行了总结与展望.     

Photon-avalanche upconversion in thulium-doped lutetium aluminum garnet.

Strong blue fluorescence at 487 nm corresponding to the (1)G(4) ? (3)H(6) transition was generated from Tm(3+)-doped lutetium aluminum garnet on excitation with a 618-nm dye laser as a result of a photon-avalanche upconversion mechanism.     

Electrophoretic deposition of alumina,yttria, yttrium aluminium garnet and lutetium aluminium garnet

The electrophoretic deposition (EPD) method has been adapted for the deposition of ceramic green bodies from aqueous nanodispersions of alumina, yttria, yttrium aluminium garnet and lutetium aluminium garnet. These materials have been selected, since they are promising candidates for optically transparent ceramics. Films as well as cylindrical bodies have been successfully prepared by application of pulsed direct current (pDC) EPD. To guarantee constant deposition yield during pDC, a variant with variable pulse widths and pulse heights has been developed. The obtained green bodies were studied by surface area analysis, scanning electron microscopy, optical transmittance measurements, determination of pycnometric density and sintering behaviour. The effect of colloid-chemical dispersion properties on green and sintered ceramics is discussed as well. The green ceramics received are nanoporous and dense, providing excellent properties for further processing under mild conditions to optical materials. For comparison, EPD-formed green bodies were either processed directly to ceramic bodies or after additional compacting by hot-pressing in a piston-cylinder apparatus.     

A magnetooptical study of the odd crystal field component in a terbium-yttrium aluminum garnet

We have studied the photoluminescence spectra and the luminescence magnetic circular polarization (LMCP) spectra in the region of the 4f-4f radiative transition ⁵D₄→⁷F₆ in the rare earth Tb³⁺ ion in a Y₃Al₅O₁₂ garnet matrix. A comparison of the experimental and theoretically calculated LMCP spectra allowed parameters of the odd crystal field component to be determined that removes the prohibition with respect to parity from the 4f-4f transitions in Tb³⁺ ion in the garnet structure. The energy spectra and wave functions of ⁵D₄ and ⁷F₆ multiplets of Tb³⁺ ion in a crystal field with the D₂ symmetry have been calculated.     

Synthesis and characterisation of chromium lutetium gallium garnet solid solution

The chromium lutetium gallium garnet system has been studied. Samples with 2xCaOxCr₂O₃(3 − 2x)Lu₂O₃5Ga₂O₃ (x = 0.025, 0.05, 0.075, 0.1, 0.2 and 0.3,) and xCr₂O₃(3 − x)Lu₂O₃5Ga₂O₃ (x = 0, 0.05, 0.075 and 0.3) compositions have been prepared in Ca,Cr:LGG and Cr:LGG systems, respectively. Samples were prepared by ceramic method, fired at 1250 °C/6 h and characterised by XRD, lattice parameters, UV-vis-NIR spectroscopy, CIE L^*a^*b^* measurements and SEM/EDX. Results indicate that Ca,Cr:LGG and Cr:LGG solid solutions are obtained. In Cr:LGG system only Cr(III) is stabilised in octahedral positions substituting for Lu(III) and Ga(III). Both Cr(III) and Cr(IV) are present in Ca,Cr:LGG. The calcium is a charge compensator to stabilise Cr(IV) and this is the predominant oxidation state up to x = 0.075 composition. From this composition, Cr(III) becomes more stabilised in garnet lattice. Cr(IV) occupies generally tetrahedral and dodecahedral sites substituting for Ga(III) and Lu(III), while Cr(III) is in octahedral site substituting for Ga(III).     

Application of nonuniform sampling in time-domain dielectric spectroscopy

Translated from Izmeritel'naya Tekhnika, No. 8, pp. 58–61, August, 1992.     

Characterization and dielectric properties of almandine-pyrope garnet

Some garnets collected from the Kothagudem area of Khammam district in Andhra Pradesh were characterized by chemical analysis. The results show the garnets to be of almandine (Fe⁺² ₃ Al₂Si₃O₁₂) pyrope (Mg₃Al₂Si₃O₁₂) group. Dielectric constant (ɛ) and dielectric loss (tanδ) were measured as a function of frequency and temperature in the frequency range of 100 Hz to 100 KHz and from room temperature to 400°C. The room temperature measurement was extended to 10 MHz, AC conductivity was calculated from the data on ε and tan δ. DC conductivity was also measured.     

Synthesis and characterization of photoluminescent cerium-doped yttrium aluminum garnet

Powder phosphor yttrium aluminum garnet (YAG), doped with trivalent cerium (Ce³⁺) is synthesized by sol-gel method. The formation of YAG and YAG:Ce (cerium-doped yttrium aluminum garnet) was investigated by means of X-ray diffraction (XRD). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were also used. The purified crystalline phases of YAG and YAG:Ce were obtained at 1000 °C. The maximum average grain size is about 20-23 nm for undoped samples and 28-34 nm for doped samples. The crystalline YAG:Ce emission shows one peak in the range 480-535 nm with the maximum near 520 nm. Photoluminescence (PL) intensity of 5d → 4f transition of Ce³⁺ increased with increasing annealing temperature. With increasing the concentration of Ce³⁺, the photoluminescence peak shifts towards the red region.     

Laser synthesis of nanopowders with yttrium aluminum garnet stoichiometry

A nanopowder of yttria-alumina mixture with the yttrium aluminum garnet (YAG) stoichiometry has been synthesized for the first time by the laser evaporation method. A high-power CO₂ laser with pulse duration above 200 μs, repetition frequency of 500 Hz, and pulse energy of about 1 J provided a high yield of powder at a rate of 24 g/h. The obtained nanopowder has been used to prepare YAG:Nd³⁺ ceramics with a cubic structure possessing an optical transmittance of about 77% at a wavelength of 1.06 μm. The successful synthesis of YAG nanopowder is based on the preliminary numerical simulation of the laser evaporation of a target using a three-dimensional model.     

Radiation resistance and chemical stability of yttrium aluminum garnet

The radiation resistance and chemical stability of yttrium aluminum garnet doped with short-lived ²⁴⁴Cm for accelerated accumulation of radiation damages was studied. Two garnet samples of the stoichiometry Y_2.8853Cm_0.1024Pu_0.0092Al₅O₁₂, containing ～4 wt % Cm with 70% content of ²⁴⁴Cm, were synthesized. The ceramics consist of the target phase of the garnet structure and a small amount of corundum. The chemical stability of the freshly prepared sample in water was studied (MCC-1 test, 90°C). The Cm leach rate is ～10^?2 g m^?2 day^?1, and that of Al and Y, ～10^?3 g m^?2 day^?1. The garnet became fully X-ray amorphous owing to self-irradiation in 530 days at the accumulated dose of 4.0 × 10¹⁸ α-disintegrations per gram, or 0.3 displacement per atom. After the destruction of the garnet structure, the Cs leach rate from the matrix 14 days after the start of the experiment increased by a factor of 10, and that of Y, by a factor of 60 relative to the freshly prepared ceramics.     

应用宽频介电谱研究氢氧化铝/环氧树脂复合材料的α和β松弛行为

聚合物的松弛行为直接影响其使用范围。本文应用宽频介电谱技术研究了中心粒径为2 μm的氢氧化铝（ATH）填料对环氧树脂复合材料α和β松弛过程的影响。宽频介电谱的测试频率范围为0.1 Hz~2 MHz,温度范围为-100~100℃。ATH填料与环氧树脂的质量比为0%、20%、40%、60%、80%和100%。结果表明：填料对复合材料的α松弛过程影响较小,Vogel温度随填料的增加先减小后增大;β松弛的表观活化能随填料的增加先增大后减小,当ATH填料质量比为40%时,β松弛的表观活化能达到最大值。