第一性原理研究钨掺杂对锐钛矿物性的影响∗

摘要

在实验上, W掺杂量在0.02083—0.04167的范围内时,有关掺杂体系的电导率影响的研究有两种相悖的结论.为解决这个问题,本文采用第一性原理平面波模守恒赝势方法,首先构建了两种Ti0.97917W0.02083O2和Ti0.95833W0.04167O2超胞模型,分别对这两种模型进行了几何结构优化、能带结构分布和态密度分布计算.同时还计算了掺杂体系的电子浓度、有效质量、迁移率和电导率.计算结果表明,在电子自旋极化或电子非自旋极化的条件下,W掺杂浓度越大、掺杂体系的电子浓度越大、有效质量越小、迁移率越小、电导率越大、导电性能越强.由电离能和Bohr半径分析进一步证实了Ti0.95833W0.04167O2超胞的导电性能优于Ti0.97917W0.02083O2超胞.为了研究掺杂体系的结构稳定性和形成能,又分别构建了Ti0.96875W0.03125O2, Ti0.9375W0.0625O2两种超胞模型,几何结构优化后进行了计算,结果表明,在电子自旋极化或电子非自旋极化的条件下,在W掺杂量为0.02083—0.04167的范围内, W掺杂浓度越大、掺杂体系的总能量越高、稳定性越差、形成能越大、掺杂越困难.将掺杂体系的晶格常数与纯的锐钛矿TiO2相比较,发现沿a轴方向的晶格常数变大、沿c轴方向的晶格常数变小、掺杂体系的体积变大,计算结果与实验结果相符合.在电子自旋极化的条件下,掺杂体系形成了半金属化的室温铁磁性稀磁半导体.%The experimental studies of the effect of W-doping on conductivity of anatase TiO2 have opposite conclusions when the W-doping concentration is in a range from 0.02083 to 0.04167. To solve the conflict, two supercell models for Ti0.97917W0.02083O2 and Ti0.95833W0.04167O2 are set up for optimizing their geometries and calculating their band structures and the densities of states based on the first-principles plane-wave norm-conserving pseudopotential of the density functional theory. The electron concentration, electron effective mass, electronic mobility, and electronic con-ductivity are calculated as well. The calculated results show that both electronic conductivity and conductive property of the doped system increase while the electron effective mass decreases, with the increase of W-doping concentration in the presence or absence of electron spin. The conductive property of Ti0.95833W0.04167O2 system is better than that of Ti0.97917W0.02083O2 system, which is further proved by the analyses of ionization energy and Bohr radius. To analyze the stability and formation energy of W-doped anatase TiO2, two more supercell models for Ti0.96875W0.03125O2 and Ti0.9375W0.0625O2 are set up combined with the geometry optimization. The calculated results show that the total en-ergy and the formation energy increase while the stability of the doped system decreases, with the increase of W-doping concentration in a range from 0.02083 to 0.04167 in the presence or absence of electron spin. Meanwhile the W-doping becomes more difficult. A comparison of the doped system with the pure anatase TiO2 shows that the lattice constant along the a-axis of the W-doped anatase TiO2 increases, and its lattice constant along the c-axis and volume increase as well. The calculated results agree with the experimental results. The doped system becomes a half-metal diluted magnetic semiconductor with a room temperature ferromagnetism in the presence of electron spin.