Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
Inorg Chem. 2011 Aug 1;50(15):6996-7003. doi: 10.1021/ic200349p. Epub 2011 Jun 29.
The structural, phonon, and thermodynamic properties of six TiO(2) polymorphs, i.e., rutile, anatase, columbite, baddeleyite, orthorhombic I, and cotunnite, have been systematically investigated by density functional theory. The predicted volumes, bulk modulus, and Debye temperature are in good agreement with experiments. The phonon dispersions of the TiO(2) polymorphs were studied by the supercell approach, whereas the long-range dipole-dipole interactions were calculated by linear response theory to reproduce the LO-TO splitting, making accurate prediction of phonon frequencies for the polar material TiO(2). The calculated phonon dispersions show that all TiO(2) polymorphs are dynamically stable at ambient pressure, indicating the high-pressure phases might be quenched to ambient conditions as ultrahard materials. Furthermore, the finite temperature thermodynamic properties of TiO(2) polymorphs were predicted accurately from the obtained phonon density of states, which is critical in the future study of the pressure-temperature phase diagram of TiO(2). The calculated Gibbs energies reveal that rutile is more stable than anatase at ambient pressure. We derived the Gibbs energy and heat capacity functions for all TiO(2) polymorphs for use in thermodynamic modeling of phase equilibria.
六种 TiO(2)多晶型物，即金红石、锐钛矿、铌铁矿、钡钛矿、正交 I 型和钙钛矿的结构、声子和热力学性质已通过密度泛函理论进行了系统研究。预测的体积、体弹性模量和德拜温度与实验吻合良好。采用超胞方法研究了 TiO(2)多晶型物的声子色散，而通过线性响应理论计算长程偶极-偶极相互作用以重现 LO-TO 分裂，从而对极性材料 TiO(2)的声子频率进行了准确预测。计算的声子色散表明，所有 TiO(2)多晶型物在环境压力下都是动力学稳定的，这表明高压相可能作为超硬材料被淬火到环境条件。此外，通过获得的声子态密度准确预测了 TiO(2)多晶型物的有限温度热力学性质，这对 TiO(2)的压力-温度相图的未来研究至关重要。计算的吉布斯能量表明，金红石在环境压力下比锐钛矿更稳定。我们推导了所有 TiO(2)多晶型物的吉布斯能量和热容函数，以便在相平衡的热力学建模中使用。
