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首页> 外文期刊>RSC Advances >Positron annihilation studies and complementary experimental characterization of xAg2O–(1 ? x)(0.3CdO–0.7MoO3) metal oxide glass nanocomposites
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Positron annihilation studies and complementary experimental characterization of xAg2O–(1 ? x)(0.3CdO–0.7MoO3) metal oxide glass nanocomposites

机译： x Ag 2 O–（1？ x ）（0.3CdO–0.7MoO 3 < / sub>）金属氧化物玻璃纳米复合材料

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Metal oxide nanocomposites of the composition xAg2O–(1 ? x)(0.3CdO–0.7MoO3) were prepared by a melt-quenching method and were characterized by different experimental techniques like X-ray diffraction, high resolution transmission electron microscopy and optical absorption spectroscopy. X-ray diffraction showed sharp diffraction peaks indicating large crystallites but transmission electron microscope images also showed crystallites of nanometer dimensions in appreciable concentrations, which confirmed the nanocomposite structure of the samples. Although the lattice constants did not show significant changes with the increase in concentration (x) of Ag2O, there is considerable relaxation of the growth-induced strain above x = 0.2. Interestingly this is also the concentration above which the optical band gap energy showed a mild decrease. One salient feature of this study is the use of positron annihilation spectroscopy for identifying and monitoring the structural defects such as vacancies and vacancy clusters as well as the free volume cavities during the change in concentration of Ag2O. Positron lifetime measurements indicated trapping of positrons initially in the interfacial defects within the 0.3CdO–0.7MoO3 nanocrystalline ensemble and then in the free volume defects within the amorphous Ag2O matrix. At higher Ag2O concentrations, positron trapping appeared to take place within the Cd2+-monovacancies in CdO and in the divacancies of neighbouring cationic and oxygen monovacancies in the α-MoO3 and CdMoO4 nanocrystallites. At x = 0.1–0.2, the effective positron trapping centres are translocated to the tetrahedral Mo6+-monovacancies instead of the Cd2+-monovacancies. The results of coincidence Doppler broadening spectroscopic measurements, which map the electron momentum distribution and its variations, indicated increasing trapping of positrons with increasing concentration of Ag2O, which again is attributed to the trapping sites in the increasing number of nanocrystallites being formed.
机译：组成为 x Ag 2 O–（1？ x ）（0.3CdO–0.7MoO的金属氧化物纳米复合材料 3 ）是通过熔融淬火法制备的，并通过X射线衍射，高分辨率透射电子显微镜和光学吸收光谱等不同的实验技术进行了表征。 X射线衍射显示出尖锐的衍射峰，表明具有大的微晶，但是透射电子显微镜图像也显示了可观浓度的纳米尺寸的微晶，这证实了样品的纳米复合结构。尽管随着Ag 2 O浓度（ x ）的增加晶格常数没有显着变化，但生长有相当大的弛豫大于 x 的应变= 0.2。有趣的是，这也是光带隙能量显示出轻微降低的浓度。这项研究的一个显着特征是使用正电子an没光谱法来识别和监测Ag 2 O。正电子寿命测量表明，正电子首先被俘获在0.3CdO–0.7MoO 3 纳米晶体集合体的界面缺陷中，然后被俘获在非晶态Ag 的自由体积缺陷中。 2 O矩阵。在较高的Ag 2 O浓度下，正电子俘获似乎发生在CdO中的Cd 2 + -单原子内。以及α-MoO 3 和CdMoO 4 纳米晶体中相邻的阳离子和氧单空位的空位。在 x = 0.1–0.2时，有效的正电子俘获中心转移到Mo 6 + 单面体的四面体而不是Cd 2 + -monovacancies。映射电子动量分布及其变化的同时多普勒加宽光谱测量结果表明，随着Ag 2 O浓度的增加，正电子的俘获也增加，这再次归因于在形成越来越多的纳米微晶中的俘获位点。

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