利用溶胶-凝胶法制备了不同组分的Zn_(0.95-x)Co_(0.05)Li_xO纳米颗粒, 并通过透射电子显微镜、 X射线衍射、紫外-可见吸收光谱和振动样品磁强计对其结构和磁性进行了系统的研究. 结果表明, 当Li掺杂比例在7%以下时, Zn_(0.95-x)Co_(0.05)Li_xO纳米颗粒仍具有很好的ZnO六角纤锌矿结构, 但随着Li掺杂量的增加, 晶格常数a和c值略有减小; Zn_(0.95-x)Co_(0.05)Li_xO的室温铁磁性随x的增大而显著增强. 当Li掺杂量达到9%时, 在Zn_(0.95-x)Co_(0.05)Li_xO纳米颗粒的XRD谱中检测出第二相的LiCoO_2団簇, 样品的铁磁磁化强度明显下降. 表征结果显示Li掺入Zn_(0.95)Co_(0.05)O的反应过程可以分为3个阶段. 前两个阶段分别在材料中引入了Li′_(Zn)深能级缺陷和Li~+填隙离子, 第三个阶段则产生了LiCoO_2第二相结构. 样品铁磁性的变化与Li掺杂引入的这些缺陷和第二相有关, 可由束缚磁极化子(BMP)模型解释.
Zn_(0.95-x)Co_(0.05)Li_xO (x=0～0.09) nanocrystals were synthesized by sol-gel method. Detailed characterization by XRD, UV-Vis absorption spectrum, and vibration sample magnetometer (VSM) indicated that Li-Co co-doping did not change the Wurtzite structure of ZnO when x≤7%. With the increase of Li-dopant, the lattice constants a and c decreased owing to the substitution of Zn~(2+) by Li~+ ions, the ferromagnetism increased gradually. However, the ferromagnetism droped sharply when Li-dopant increased to 9%. At the same time, second-phase clusters of LiCoO_2 were detected in the XRD pattern and the lattice constants almost stopped decreasing. Experimental results suggested that the reaction of Li incorporation could be divided into 3 stages. Li′_(Zn) deep-level defects and Li_i~+ interstitials were induced into the material at the former two stages respectively, while the second-phase LiCoO_2 formed at the third stage. These defects and second-phase structures induced by Li-doping played important roles in enhancing the ferromagnetism of the samples, which could be explained by the bound magneton polaron (BMP) model.
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