Olson Carol L, Nelson Jenny, Islam M Saiful
Department of Physics, Blackett Laboratory, Imperial College London, UK.
J Phys Chem B. 2006 May 25;110(20):9995-10001. doi: 10.1021/jp057261l.
Atomistic simulation techniques are used to investigate the defect properties of anatase TiO(2) and Li(x)TiO(2) both in the bulk and at the surfaces. Interatomic potential parameters are derived that reproduce the lattice constants of anatase, and the energies of bulk defects and surface structures are calculated. Reduction of anatase involving interstitial Ti is found to be the most favorable defect reaction in the bulk, with a lower energy than either Frenkel or Schottky reactions. The binding energies of selected defect clusters are also presented: for the Ti(3+)-Li(+) defect cluster, the binding energy is found to be approximately 0.5 eV, suggesting that intercalated Li ions stabilize conduction band electrons. The Li ion migration path is found to run between octahedral sites, with an activation energy of 0.45-0.65 eV for mole fractions of lithium in Li(x)TiO(2) of x < or = 0.1. The calculated surface energies are used to predict the crystal morphology, which is found to be a truncated bipyramid in which only the (101) and (001) surfaces are expressed, in accord with the available microscopy data. Calculations of defect energies at the (101) surface suggest that single Ti(3+) defects and neutral Ti(3+)-Li(+) pairs tend to segregate to the surface.
原子模拟技术用于研究锐钛矿型TiO₂和LiₓTiO₂在体相和表面的缺陷性质。推导了能够重现锐钛矿晶格常数的原子间势参数，并计算了体相缺陷和表面结构的能量。发现涉及间隙Ti的锐钛矿还原是体相中最有利的缺陷反应，其能量低于弗伦克尔或肖特基反应。还给出了选定缺陷簇的结合能：对于Ti³⁺-Li⁺缺陷簇，发现结合能约为0.5 eV，这表明嵌入的Li离子使导带电子稳定。发现Li离子迁移路径在八面体位置之间，对于x≤0.1的LiₓTiO₂中锂的摩尔分数，活化能为0.45 - 0.65 eV。计算得到的表面能用于预测晶体形态，发现其为截顶双锥体，其中仅表现出(101)和(001)表面，这与现有的显微镜数据一致。(101)表面缺陷能量的计算表明，单个Ti³⁺缺陷和中性Ti³⁺-Li⁺对倾向于偏析到表面。
