Mg_2Si热电特性的第一性原理研究
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摘要
运用基于密度泛函理论的第一性原理方法计算了Mg_2Si晶体中原子间的相互作用势能、电子的能带结构、声子谱、声子态密度和热力学参数.计算结果表明:当Mg_2Si晶体中各原子处在平衡位置时,Mg-Mg键的势能最大,其次为Mg-Si键,Si-Si键最小,Mg_2Si晶体禁带宽度为0.217eV,属于间接带隙半导体,通过振动频谱及声子态密度图可知,存在9条色散关系曲线,其中3条为声学波,6条为光学波,且频率在280cm~(-1)附近的格波振动较强.随着温度的增加,熵、内能均增加,而亥姆霍兹自由能减少.当温度低于200K时,比热容随着温度的增加显著增加,在低温范围内符合德拜模型.当温度高于400K时,比热容符合爱因斯坦模型,其值接近于常数CV=74.8J·mol/K.
The first-principles method based on density functional theory was used to calculate the interaction potential energy,electron band structure,phonon spectrum,phonon state density and thermodynamic parameters of atoms in Mg_2Si crystal.The calculation results show that when the atoms in the Mg_2Si crystal are in equilibrium,the potential energy of the Mg-Mg bond is the largest,followed by the Mg-Si bond,the Si-Si bond is the smallest,and the forbidden band width of the Mg_2Si crystal is 0.217 eV,which belongs to the indirect band gap.Semiconductors,through the vibration spectrum and phonon state density map,there are 9 dispersion curves,of which 3 are acoustic waves,6 are optical waves,and the lattice wave vibration near 280 cm~(-1) is strong.As the temperature increases,the entropy and internal energy increase,while the Helmholtz free energy decreases.When the temperature is lower than 200 K,the specific heat capacity increases significantly with the increase of temperature,and conforms to the Debye model in the low temperature range.When the temperature is higher than 400 K,the specific heat capacity is in accordance with the Einstein model,and the specific heat capacity is close to the constant CV=74.8 J·mol/K
The first-principles method based on density functional theory was used to calculate the interaction potential energy,electron band structure,phonon spectrum,phonon state density and thermodynamic parameters of atoms in Mg_2Si crystal.The calculation results show that when the atoms in the Mg_2Si crystal are in equilibrium,the potential energy of the Mg-Mg bond is the largest,followed by the Mg-Si bond,the Si-Si bond is the smallest,and the forbidden band width of the Mg_2Si crystal is 0.217 eV,which belongs to the indirect band gap.Semiconductors,through the vibration spectrum and phonon state density map,there are 9 dispersion curves,of which 3 are acoustic waves,6 are optical waves,and the lattice wave vibration near 280 cm~(-1) is strong.As the temperature increases,the entropy and internal energy increase,while the Helmholtz free energy decreases.When the temperature is lower than 200 K,the specific heat capacity increases significantly with the increase of temperature,and conforms to the Debye model in the low temperature range.When the temperature is higher than 400 K,the specific heat capacity is in accordance with the Einstein model,and the specific heat capacity is close to the constant CV=74.8 J·mol/K
引文
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[8]Hiroshi Mizoguchi,Yoshiinori Muraba,Daniel C.The Unique Electronic Structure of Mg2Si:Shaping the Conduction Bands of Semiconductors with Multicenter Bonding[J].Angewandte Chemie International Edition,2017,56(34):10135-10139.
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[3]郭连权,林琳,马贺,刘虹辰.Mg2Si的声子谱与热学性能的第一性原理计算[J].沈阳工业大学学报,2015,37(3):294-298.
[4]王彦成,邱吴劼,杨宏亮,等.基于第一性原理分子动力学的填充方钴矿热输运性质及微观过程的研究[J].物理学报,2018,67(1):016301-1-016301-10.
[5]Noda,Y.,Kon H.,Furukawa Y.,et al.Preparation and thermoelectric properties of Mg2Si1-xGex(x=0.0~0.4)solid solution semiconductors[J].Materials Transactions,1992,33(9):845-850.
[6]Yu B.,Chen D.,Tang Q.,et al.Structural,electronic,elastic and thermal properties of Mg2Si[J].Journal of Physics Chemistry of Solids.2010,71(5):758-763.
[7]Yu R.,Zhai P.C.,Li G.D.,et al.Molecular Dynamics Simulation of the Mechanical Properties of Single-Crystal Bulk Mg2Si[J].Journal of Electronic Materials,2012,41(6):1465-1469.
[8]Hiroshi Mizoguchi,Yoshiinori Muraba,Daniel C.The Unique Electronic Structure of Mg2Si:Shaping the Conduction Bands of Semiconductors with Multicenter Bonding[J].Angewandte Chemie International Edition,2017,56(34):10135-10139.