基于密度泛函的方法研究了β-La_2Mo_2O_9的结构性质与扩散行为.研究首次发现结构中Mo有MoO_4和MoO_5 2种形式的多面体,并且O(1)、O(2)和O(3)3种氧位置的占有率分别为100%、91.7%和25%,与实验相 ,符.所有结构可通过P2_13的12个对称操作而互相转换,得到的结构可能是局部或本征极小结构.扩散研究结果显示,氧离子(空位)扩散是一种多离子间协同的集体运动行为,3个扩散通道可能与高温相的高电导有关,其中激活能为1.05eV和1.24eV的2个扩散通道可能与内耗弛豫峰有关.
The structure and diffusion of β-La_2Mo_2 O_9 are studied with the framework of the density-functional theory. It is found that the occupancies of three crystallographic distinct O sites O(1), O(2) and O(3) are 100%, 91.7% and 25%, respectively, consistent with experiments. Each Mo cation is surrounded by four or five Oions. All configurations are related to each other by one of 12 symmetry operations of P2_13 space group, the structure observed experimentally may be interpreted as a time and spatial average of these local or inherent structures. The O ions move in a cooperative fashion. Three diffusion channels are found to be responsible for the high conductivity, and two channels with activation energies of 1.05eV and 1.24eV to be responsible for mechanical relaxation peaks.
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