X-Ray Diffraction Line Broadening: Modeling and Applications to High-Tc Superconductors

A method to analyze powder-diffraction line broadening is proposed and applied to some novel high-T_c superconductors. Assuming that both size-broadened and strain-broadened profiles of the pure-specimen profile are described with a Voigt function, it is shown that the analysis of Fourier coefficients leads to the Warren-Averbach method of separation of size and strain contributions. The analysis of size coefficients shows that the “hook” effect occurs when the Cauchy content of the size-broadened profile is underestimated. The ratio of volume-weighted and surface-weighted domain sizes can change from ~1.31 for the minimum allowed Cauchy content to 2 when the size-broadened profile is given solely by a Cauchy function. If the distortion co-efficient is approximated by a harmonic term, mean-square strains decrease linearly with the increase of the averaging distance. The local strain is finite only in the case of pure-Gauss strain broadening because strains are then independent of averaging distance. Errors of root-mean-square strains as well as domain sizes were evaluated. The method was applied to two cubic structures with average volume-weighted domain sizes up to 3600 Å, as well as to tetragonal and orthorhombic (La-Sr)₂CuO₄, which exhibit weak line broadenings and highly overlapping reflections. Comparison with the integral-breadth methods is given. Reliability of the method is discussed in the case of a cluster of the overlapping peaks. The analysis of La₂CuO₄ and La_1.85M_0.15CuO₄(M = Ca, Ba, Sr) high-T_c superconductors showed that microstrains and incoherently diffracting domain sizes are highly anisotropic. In the superconductors, stacking-fault probability increases with increasing T_c; microstrain decreases. In La₂CuO₄, different broadening of (h00) and (0k0) reflections is not caused by stacking faults; it might arise from lower crystallographic symmetiy. The analysis of Bi-Cu-O superconductors showed much higher strains in the [001] direction than in the basal a-b plane. This may be caused by stacking disorder along the c-axis, because of the two-dimensional weakly bonded BiO double layers. Results for the specimen containing two related high-T_c phases indicate a possible mechanism for the phase transformation by the growth of faulted regions of the major phase.     

J75不锈钢淬火应力的X射线衍射分析

利用铬靶X射线在侧倾结合固定ψ法基础上对J75不锈钢的（311）面进行了淬火应力测量,得到了不同淬火温度下J75合金试样中心点的残余应力值和近表面微应变效应。结果表明：试样表面残余压应力值在-400～-650MPa,最大值出现在淬火温度为700℃左右;淬火使衍射峰半高宽由1．25°增加至1．4°以上,显著增加了J75合金的位错等缺陷。受淬火瞬时热应力分布影响,越靠近试样表面衍射峰的宽化越严重。     

铜薄膜微结构的X射线衍射线形分析

首先采用真空蒸镀法制备了不同厚度的铜薄膜,并对薄膜进行了退火处理;然后用X射线衍射仪测定铜薄膜的衍射谱,最后采用线形分析法对衍射谱进行计算,得到了不同厚度铜薄膜退火前后的晶粒尺寸和微应变。结果表明:真空蒸镀铜薄膜晶粒尺寸随薄膜厚度的增加而增大,微应变随薄膜厚度的增加而减小;退火处理后薄膜晶粒明显长大,薄膜微应变在退火处理后明显减小。     

双辊淬冷法制备稀土镍基贮氢合金及其晶粒尺寸和电化学性能

使用双辊淬冷技术制备了LaNi5基AB5型贮氢合金,用扫描电镜和X射线衍射确定合金的晶粒尺寸,用恒电流充放电方法确定合金的电化学容量及其循环稳定性.结果表明, 制备的合金具有均匀的纳米晶结构;在64mA/g(约0.2C)的电流密度下,合金放电容量高达336mAh/g,而在640mA/g(约2C)的电流密度下,合金放电容量仍达312mAh/g,经400次循环后容量保持约80%.另外,还研究了La含量对合金容量和循环稳定性的影响,合金容量在La 含量<60%范围内,随La含量增加而增加,La含量从60%增至80%,合金容量保持不变, 但是合金循环稳定性随La含量增加而减少.     

密堆六方纳米ZnO的X射线衍射表征与研究

X射线衍射(XRD)实验发现密堆六方纳米ZnO的hk0、h-k=3n的衍射线, 仅存在微晶宽化, 而h-k=3n±1的衍射线, 无l=偶数、l=奇数的层错选择宽化效应. 为了表征这种纳米ZnO的晶粒大小和层错几率, 提出了分解纳米ZnO微晶-层错二重宽化效应的最小二乘法. 计算结果表明: 密堆六方纳米ZnO的晶粒大小和层错几率与制备方法、原料配比等有关.     

激光粒度仪颗粒联测的结果与评价

为了解不同激光粒度仪的硬件、软件等方面差异对粒度测量结果的影响,用4种颗粒形状不同的粉末在不同公司生产的激光粒度仪上进行测试。结果表明:激光粒度仪测试结果重复性很好;对于球形粉末和形状较规则的粉末,大部分激光粒度仪测得的中位径值之间可以比较;而粒径范围较宽和不规则形状粉末,个别仪器测量的中位径值有差异。     

基于电子背散射衍射分析晶粒大小分布和微观织构的关系

采用电子背散射衍射技术检测了三种薄钢板试样的晶粒尺寸统计分布规律,并测定了取向成像图和取向分布函数图,统计了各织构晶粒所占比率以及晶粒取向差分布状况。分析了晶粒大小统计分布状况对微观织构形成的影响。结果表明:晶粒尺寸分布越集中,越利于增加{111}∥ND有利织构的含量;取向成像图和取向分布函数图所分析的织构结果是一致的,晶粒取向差分布状况与织构特征的形成有一定的对应关系。