共查询到20条相似文献,搜索用时 390 毫秒
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通过对K2WO4和K2W2O7两种助溶剂的对比、分析,选择K2W2O7做助溶剂,采用顶部籽晶(TSSG)法生长YbKGW晶体.设计了合理的工艺条件转速10~15r/min;降温速率0.05℃/h;生长周期15d.通过对YbKGW晶体粉末样品的X-ray衍射谱与KGW粉末样品的X-ray衍射谱对比分析,生长晶体为β-YbKGW晶体.利用TG-DTA测定YbKGW晶体的熔点及相变温度分别是1086℃和1021℃.通过对晶体缺陷的观察分析认为,晶体裂缝及包裹物等缺陷与生长工艺条件密切相关,应尽量减少生长过程中的温度、浓度及生长速度的波动,保持晶体的稳态生长. 相似文献
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Bi12GeO20晶体是一种多功能光电材料,在可见光范围内具有高速光折变响应,以及良好的压电、声光、磁光,旋光和电光等性能。目前,提拉法生长Bi12GeO20晶体,存在生长成本高、晶锭形状不规则、生长产率低、晶体光学质量差和有效晶体截面小等问题。本研究率先采用改进的坩埚下降法,在铂金坩埚和空气气氛中生长大尺寸Bi12GeO20晶体。通过各种分析测试方法研究生长获得的Bi12GeO20晶体中宏观缺陷的形态、分布和成分构成,探讨了晶体生长过程中主要宏观缺陷的形成过程和成因。坩埚下降法生长的Bi12GeO20晶体存在两种主要宏观缺陷:枝蔓状和管状包裹体。其中,枝蔓状包裹体与铂金溶蚀后的析晶相关,而管状包裹体与铂金析出、接种界面不稳定性和温度波动有关。本研究提出了消除坩埚下降法生长晶体中宏观缺陷的技术途径,通过降低生长控制温度、缩短高温熔体保持时间和优选籽晶等措施,可重复地生长... 相似文献
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采用真空坩埚下降法在石墨坩埚中生长了大尺寸CaF2晶体.通过高温氟化获得无水高纯原料,自发成核发育籽晶,以<2mm/h的生长速率,成功生长了直径170mm的CaF2晶体.研究了晶体的顶部析晶形貌、包裹体、解理等生长缺陷. 相似文献
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Yb:KGd(WO4)2激光晶体结构与振动光谱 总被引:1,自引:0,他引:1
用顶部籽晶提拉法,以K2W2O7为助溶剂,生长YbKGd(WO4)2激光晶体.经热重-差热分析,确定晶体熔点为1086℃,相变温度为1021℃.晶体结构分析确定YbKGW(WO4)2晶体由WO6八面体连接而成,WO6八面体是由(WOOW)双氧桥及(WOW)单氧桥构成.晶体粉末样品室温下的红外及拉曼光谱测试,确定WO42-、双氧桥及单氧桥的振动范围,并对其进行了归属.X射线粉末衍射测试,验证所生长的晶体为β-YbKGd(WO4)2. 相似文献
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La0.67Ca0.33MnO3 (LCMO)/La0.67Sr0.33CoO3 (LSCO)/LCMO trilayer films are fabricated on single-crystal substrates NdGaO3 (110) and the interlayer coupling are investigated. Compared with LCMO single layer, sandwiches showed the enhanced metal-insulator transition temperature of LCMO layers. The magnetoresistance is dependent on spacer thickness and the peak value dramatically decreases when LSCO layer is thick enough because of shorting by the LSCO layer. The magnetic coercivity HC shows a nonmonotonic behavior with changing spacer layer thickness and the waist-like hysteresis indicates that there is an indirect exchange coupling between the top and bottom LCMO layers across the spacer layer. 相似文献
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Choon-W. Nahm 《Materials Letters》2011,65(9):1299-1301
The varistor properties of the ZnO-Pr6O11-CoO-Cr2O3-Y2O3-In2O3 ceramics were investigated for different concentrations of In2O3. The increase of In2O3 concentration slightly increased the sintered density (5.60-5.63 g/cm3) and slightly decreased the average grain size (3.4-2.9 μm). The breakdown field increased from 6023 to 14822 V/cm with increasing concentration of In2O3. The nonlinear coefficient increased from 17.6 to 44.6 for up to 0.005 mol%, whereas the further doping caused it to decrease to 36.8. In2O3 acted as an acceptor due to the donor concentration, which decreases in the range of 1.02 × 1017 to 0.24 × 1017/cm3 with increasing concentration of In2O3. 相似文献
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Transparent glasses in the system (100−x)Li2B4O7–x(SrO---Bi2O3---Nb2O5) (10≤x≤60) (in molar ratio) were fabricated by a conventional melt-quenching technique. Amorphous and glassy characteristics of the as-quenched samples were established via X-ray powder diffraction (XRD) and differential thermal analyses (DTA) respectively. Glass–ceramics embedded with strontium bismuth niobate, SrBi2Nb2O9 (SBN) nanocrystals were produced by heat-treating the as-quenched glasses at temperatures higher than 500 °C. Perovskite SBN phase formation through an intermediate fluorite phase in the glass matrix was confirmed by XRD and transmission electron microscopy (TEM). Infrared and Raman spectroscopic studies corroborate the observation of fluorite phase formation. The dielectric constant (r) and the loss factor (D) for the lithium borate, Li2B4O7 (LBO) glass comprising randomly oriented SBN nanocrystals were determined and compared with those predicted based on the various dielectric mixture rule formalism. The dielectric constant was found to increase with increasing SBN content in LBO glass matrix. 相似文献
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G. R. Gurbanov 《Inorganic Materials》2012,48(9):888-890
Phase equilibria along the PbSbBiS4-Sb2S3 and PbSbBiS4-Bi2S3 joins of the PbS-Sb2S3-Bi2S3 system have been studied for the first time using differential thermal analysis, X-ray diffraction, microstructural analysis, microhardness tests, and density measurements, and the phase diagrams of the joins have been mapped out. The joins are shown to be pseudobinary with limited series of terminal solid solutions. The solid solutions are p-type semiconductors. 相似文献
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Hollandite-type compounds, Rb2Cr8O16, K2Cr2V6O16 and K2V8O16, were synthesized under high P-T conditions up to 1200°C and 7GPa. The structural refinement using a single crystal of Rb2Cr8O16 confirms that the structure is similar to that of K2Cr8O16. Magnetic measurements indicate that Rb2Cr8O16 is ferromagnetic below 295K, K2Cr2V6O16 paramagnetic down to 77K and K2V8O16 has susceptibility anomaly at 175K. These compounds are all semiconductive and show discontinuities in temperature-resistivity curves at points corresponding to magnetic anomalies. 相似文献
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Epitaxial YBa2Cu3O7/La0.7Ca0.3MnO3 (YBCO/LCMO) bi-layers and La0.7Ca0.3MnO3/YBa2Cu3O7 (LCMO/YBCO) bi-layers were grown on (001)LaAlO3 by pulsed laser deposition, and their microstructures were compared by transmission electron microscopy investigation. In the YBCO(100 nm)/LCMO(150 nm) bi-layers, the LCMO layer consists of columnar grains of ~ 17 nm in diameter and contains mixed orientation domains of [100]c, [010]c and [001]c. The YBCO layer is totally c-axis oriented and the YBCO lattices are tilted − 2.5° to + 2.5° as they grew on the rough surfaces of LCMO columnar grains. For the LCMO(140 nm)/YBCO(140 nm) bi-layers, the LCMO/YBCO interface is sharp and flat. The initial 12-nm thickness of the YBCO layer is composed of c-axis oriented domains, and the upper part of YBCO layer is [100] oriented. The LCMO layer was predominantly [001]c oriented while [100]c-oriented domains were occasionally observed. 相似文献
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We investigated the structural and superconducting properties ofc-axis oriented (YBa2Cu3O7)
nY
/(PrBa2Cu3O7)
npr
superlattices with thicknesses of the individual layers down to one unit cell (10nY1; 18>nPr 1). By transmission electron microscopy and X-ray diffraction we find an excellent structural quality of the samples, though the quantitative analysis shows the existence of defects. In superlattices with decoupled YBa2Cu3O7 layers of two unit cell thickness we find a highT
c
value of 75 K. We probed the flux line structure in the superlattices by measurements of the critical current density in magnetic fields. The experiments show that the flux-line dynamics is dominated by the movement of pancake vortices. 相似文献
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A systematic study was performed with mixtures consisting of N2, CH4, C2H6 and C3H8, to investigate experimentally phase equilibria and caloric properties and to test the accuracy of thermodynamic correlations. The first part of this Paper reports results of T---p---x---y measurements on ternary systems in the range 20 < p < 120 bar and 140 < T < 220 K. The results are compared with data calculated by generalized equations of state. 相似文献
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J.A. Luna-Lpez J. Portelles O. Raymond J.M. Siqueiros 《Materials Chemistry and Physics》2009,118(2-3):341-348
Sr0.3Ba0.7Nb2O6 (SBN) and La0.030Sr0.255Ba0.700Nb2O6 (LSBN) ceramic compounds have been prepared using the traditional ceramic method at two different calcination temperatures (900 and 1000 °C) and later sintered both at 1400 °C. A study of the effects of the calcination temperatures and La substitution on the morphological, compositional, and structural properties of SBN and LSBN is presented using scanning electronic microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) analysis. From Rietveld refinement processes, the XRD patterns were interpreted to evaluate such effects in the structural parameters and the site occupation factors of the heavy metals and oxygen atoms. The effect of the incorporation of La resulted in a 0.25% cell contraction and turned out to be higher than the 0.08% dilation effect produced by the increase of calcination temperature. The La ion with similar effective ionic radius and higher electronegativity is incorporated into the structure occupying the A1 site just like the Sr ions in the SBN compound. Differences in the site occupation factors between the SBN and LSBN samples lead to substantial changes in the physical properties such as temperature of relative dielectric constant maximum, relative dielectric constant, and dielectric loss, correlated with the distortion and the relative orientation of the oxygen octahedra. 相似文献
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Xiaohua Sun Ying YangQiaoling Zhang Zhimeng LuoShuang Hou Caihua HuangJun Zou 《Materials Science and Engineering: B》2013,178(18):1244-1248
Bi1.5Zn0.5Nb0.5Ti1.5O7 (BZNT) thin films with different thicknesses as cover layers were deposited on the Ba0.6Sr0.4TiO3 (BST) thin films on the Pt/Ti/SiO2/Si substrates by radio frequency magnetron sputtering method. The microstructure, surface morphology, dielectric and tunable properties of BST/BZNT heterogeneous bilayered films were investigated as a function of the thickness of BZNT films and the effect of BZNT films on the asymmetric electrical properties of BST/BZNT bilayered films was discussed. It was found that BZNT cover layer significantly improved the leakage current and the dielectric loss, and the dielectric constant and tunability of BST/BZNT bilayered thin films simultaneously decreased with the increasing thickness of BZNT films. The BST/BZNT bilayered thin film with a 50 nm BZNT cover layer gave the largest figure of merit (FOM) of 33.48 with the upper tunability of 55.38%. The asymmetric electrical behavior of BST/BZNT bilayered films is probably related to an internal electric field caused by built-in voltages at Pt/BST and BZNT/Au interfaces. 相似文献