The electronic structure, magnetic states, chemical bonding, and thermodynamic properties of β-US2 are investigated by using first-principles calculation through the density functional theory（DFT） ＋U approach. The...The electronic structure, magnetic states, chemical bonding, and thermodynamic properties of β-US2 are investigated by using first-principles calculation through the density functional theory（DFT） ＋U approach. The obtained band structure exhibits a direct band gap semiconductor at Γ point with a band gap of 0.9 e V for β-US2, which is in good agreement with the recent experimental data. The charge-density differences, the Bader charge analysis, and the Born effective charges suggest that the U–S bonds of the β-US2 have a mixture of covalent and ionic characters, but the ionic character is stronger than covalent character. The Raman-active, infrared-active, and silent modes at the Γ point are further assigned and discussed. The obtained optical-mode frequencies indicate that the three apparent LO–TO（longitudinal optical–transverse optical） splittings occur in B1 u, B2 u, and B3 umodes, respectively. Furthermore, the Helmholtz free energy ？F, the specific heat ？E, vibrational entropy S, and constant volume CVare studied over a range from 0 K-100 K. We expect that our work can provide some valuable information for further experimental investigation of the dielectric properties and the infrared reflectivity spectrum of uranium chalcogenide.展开更多
采用固相烧结法制备了(W0.5Mg0.5)^4+复合离子掺杂的(Bi0.5Na0.5)0.94Ba0.06Ti1-x(W0.5Mg0.5)xO3(BNBT-x WM)无铅陶瓷,研究了(W0.5Mg0.5)^4+复合离子掺杂量对BNBT陶瓷的表面形貌、微观结构,以及铁电、应变、压电、介电等电学性能的影响...采用固相烧结法制备了(W0.5Mg0.5)^4+复合离子掺杂的(Bi0.5Na0.5)0.94Ba0.06Ti1-x(W0.5Mg0.5)xO3(BNBT-x WM)无铅陶瓷,研究了(W0.5Mg0.5)^4+复合离子掺杂量对BNBT陶瓷的表面形貌、微观结构,以及铁电、应变、压电、介电等电学性能的影响。结果表明:(W0.5Mg0.5)^4+复合离子进入了BNBT陶瓷的B位并形成了单一的钙钛矿结构,且陶瓷样品晶界清晰,结构致密。(W0.5Mg0.5)^4+掺杂增大了剩余极化强度和饱和极化强度。(W0.5Mg0.5)^4+复合离子的掺杂使电致应变曲线由蝴蝶形变为嫩芽形,在x=0.03时获得0.429%(质量分数)的高电致应变响应,d33*的最大值为833.1 pm/V,其外加高场仅有60 k V/cm。在x=0.02时其低场小信号的压电性能d33有235 p C/N。BNBT-x WM陶瓷的介电常数随着掺杂含量的增多逐渐降低且平坦化,同时向弛豫铁电体转变。展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.21371160 and 21401173)
文摘The electronic structure, magnetic states, chemical bonding, and thermodynamic properties of β-US2 are investigated by using first-principles calculation through the density functional theory（DFT） ＋U approach. The obtained band structure exhibits a direct band gap semiconductor at Γ point with a band gap of 0.9 e V for β-US2, which is in good agreement with the recent experimental data. The charge-density differences, the Bader charge analysis, and the Born effective charges suggest that the U–S bonds of the β-US2 have a mixture of covalent and ionic characters, but the ionic character is stronger than covalent character. The Raman-active, infrared-active, and silent modes at the Γ point are further assigned and discussed. The obtained optical-mode frequencies indicate that the three apparent LO–TO（longitudinal optical–transverse optical） splittings occur in B1 u, B2 u, and B3 umodes, respectively. Furthermore, the Helmholtz free energy ？F, the specific heat ？E, vibrational entropy S, and constant volume CVare studied over a range from 0 K-100 K. We expect that our work can provide some valuable information for further experimental investigation of the dielectric properties and the infrared reflectivity spectrum of uranium chalcogenide.
文摘采用固相烧结法制备了(W0.5Mg0.5)^4+复合离子掺杂的(Bi0.5Na0.5)0.94Ba0.06Ti1-x(W0.5Mg0.5)xO3(BNBT-x WM)无铅陶瓷,研究了(W0.5Mg0.5)^4+复合离子掺杂量对BNBT陶瓷的表面形貌、微观结构,以及铁电、应变、压电、介电等电学性能的影响。结果表明:(W0.5Mg0.5)^4+复合离子进入了BNBT陶瓷的B位并形成了单一的钙钛矿结构,且陶瓷样品晶界清晰,结构致密。(W0.5Mg0.5)^4+掺杂增大了剩余极化强度和饱和极化强度。(W0.5Mg0.5)^4+复合离子的掺杂使电致应变曲线由蝴蝶形变为嫩芽形,在x=0.03时获得0.429%(质量分数)的高电致应变响应,d33*的最大值为833.1 pm/V,其外加高场仅有60 k V/cm。在x=0.02时其低场小信号的压电性能d33有235 p C/N。BNBT-x WM陶瓷的介电常数随着掺杂含量的增多逐渐降低且平坦化,同时向弛豫铁电体转变。
