稀土钠钨青铜化合物Na_xLa_yWO_3结构与导电性的理论研究

Theoretical Study on the Structure and Conductivity of Tungsten Bronzes Na_xLa_yWO_3

使用密度泛函理论研究了稀土钠钨青铜化合物的结构和导电性质.在实验晶体结构数据的基础上构建NaxWO3和NaxLayWO3的模型分子,优化其几何结构,并与实验值比较.在此基础上计算了化合物的能带结构和电子能态密度.通过这些研究探讨当La3+取代NaxWO3的中心Na+后对结构和导电性的影响.计算结果表明La3+的取代并没有改变结构的空间对称性,但却使晶格参数和体积略有增大;取代使电子结构发生了变化,在费米面附近,能带相互交叠更加密集,电子出现的几率增加,从而增加了其导电性.这可能是掺杂后La3+的4f和5d电子的贡献使电子轨道杂化作用增强,电子云密度分布重排的结果.

The geometric structures and electronic structures of tungsten bronzes NaxWO3 and Nax- LayWO3 （x〉0.36, y〈0.015） have been explored by density functional theory （DFT）. The geometry was optimized using ADF （Amsterdam density functional） program package with TZ2P basis set. The energy bands and density of states were calculated using the VASP （Vienna ab-initio simulation package） program. The calculated structures are close to the experimental values. After the substitution of La^3＋ for Na^＋, the space symmetry is not changed but the lattice parameters and volumes of NaxLayWO3 increase. The energy bands are condensed and the appearance probabilities of the electrons are enhanced near the Fermi-surface. Therefore, the introduction of La^3＋ is important to improve the conductivity of the sodium tungsten bronze.