第一性原理研究高温高压下TiB2的物理性质

First-principles study on the physical properties of TiB2 under high temperature and high pressure

摘要:

采用第一原理方法计算TiB2在高温高压下的物理性质. 对结构参数、弹性常数、体积模量、能带结构、声子色散、热力学性质等进行了密度泛函理论计算. 计算结果与其他实验和理论计算值吻合较好. 通过对E-V曲线、声子色散曲线和态密度(DOS)的分析，证明TiB2是机械稳定的. 从B/G和泊松比的两种方法得到了TiB2的脆性行为. 在准谐振德拜模型的基础上, 计算分析了德拜温度Θ和热膨胀系数对温度和压强的依赖. 并从不同压强下定容比热容随温度变化的曲线图中得出，在T=1300 K以后，CV无限靠近Dulong-Petit极限. 通过分析电子态密度，发现TiB2具有金属性，并且随着压强的增大费米能级处峰值降低，赝能隙变宽，非局域化加大，共价键作用增强，从而也证明了晶体结构的稳定性.

Abstract:

This work reports the calculations of the physical properties of TiB2 under high temperature and high pressure using the first-principles method. The calculations include the structural parameter, elastic constants, bulk modulus, band structure, phonon dispersion, thermodynamic properties. These results are in agree well with other experimental and theoretical calculated values. By analyzing the E-V curves, the phonon dispersion curve, and the density of states (DOS), we prove that TiB2 is mechanically stable. From the results of B/G ratio and Poisson's ratio, the brittleness behavior of TiB2 is obtained. On the basis of the quasi-harmonic Debye model, we calculate the Debye temperature Θ and analyze the temperature and pressure dependences of the thermal expansion. The volumetric specific heat is very close to the Dulong-Petit limit at 1300 K. By analyzing the electron state density, it is found that TiB2 has metallic properties, the peak at Fermi level decreases, the pseudo gap widens, non-localization increases and covalent bond is enhanced as the pressure increases. All these results have proved that the crystal structure of TiB2 is stable.