金属W掺杂AgSnO_(2)材料导电性能研究

Conductivity of Metal W-doped AgSnO_(2) Materials

AgSnO_(2)作为电接触材料成功替代AgCdO材料,但是使用过程中析出的SnO_(2)是宽禁带半导体,在导电性方面同AgCdO材料相比较差,因此决定通过掺杂W元素来提升SnO_(2)材料的导电性。依据第一性原理,利用Material Studio软件中的CASTEP模块对SnO_(2)晶体进行不同浓度比(50%,25%,16.7%,12.5%,8.35%,6.25%,5%)的W元素掺杂,并计算其结构参数、焓变、能带结构、态密度、电荷布局等特性。分析得出,任意掺杂后的SnO_(2)结构较未掺杂前焓变绝对值增大,新生成O-W键与O-Sn键键长相差不大,掺杂后可以生成稳定结构;由于W元素的掺杂,其特有的d轨道不仅能提供更多能量,同时与O的耦合作用使能带间隙减小,当掺杂比为6.25%时其间隙可减小到0.008 eV,能带图中导带底与价带顶近似重合;掺杂后总电荷量增加,载流子浓度提升;通过计算确定在掺杂比为6.25%时材料的导电性最好,电导率较未掺杂前有大幅度提升。计算结果为后续研究提供了理论基础。

The contact was a frequently used component in the relay,and its performance directly affected the service life of the relay.After the moving and static contacts were in contact with each other for a long time,the contact affected the contact resistance of the material due to friction and high temperature,and then affected the work of the contact.Therefore,this article chose to improve the current situation by improving the contact material.As a representative of the contact material,AgCdO material generated chromium vapor during use,pollute water sources and crops,and affected human life safety.In the RoHS2.0 directive issued by the European Union in 2015,it was stated that starting from July 2019,the import of Cd-containing electronic and electrical products with a mass fraction of 0.01%higher than the mass fraction of 0.01%would be restricted.Therefore,AgCdO materials had gradually faded out of people’s vision,and scholars had begun to work hard.For the selection of safer and more efficient electrical contact materials,the emergence of AgSnO_(2) successfully replaced AgCdO materials.However,the AgSnO_(2) material formed a high-temperature arc due to the collision between the contacts during use,forming a molten liquid on the surface of the contacts,and finally precipitated SnO_(2) crystals after cooling,and SnO_(2)was a wide bandgap semiconductor with poor conductivity.At the same time,the melting point was high and it was not easy to decompose at low temperature.Its attachment to the surface of the contact material affects the service life of the contact.The influencing factors of electrical contact materials in the contact working process were more complicated.This article mainly used doping elements to improve the conductivity of SnO_(2) materials.W had good high temperature resistance and was in the position of transition metal in the periodic table.It had the advantage of moderate electronegativity,that was,the conductivity of AgSnO_(2) was improved by adding W element to SnO_(2).Material Studio software was based on first principles to perform simulation calculations,and was widely used to calculate various properties of materials.The CASTEP module combined plane wave pseudopotential basis set with density functional theory,visualized the model,and solved various problems related to physical properties.On the basis of exporting the SnO_(2) unit cell structure in the material library,the CASTEP module in the Material Studio software was used to do SnO_(2) crystals with different concentration ratios of W(50%,25%,16.7%,12.5%,8.35%,6.25%,5%)element doping,and optimize the structure of different doping conditions.The structure was optimized for different doping situations,and its structure parameters,enthalpy change,energy band structure,density of state,charge population and other characteristics were calculated.The analysis showed that the absolute value of the enthalpy change of the SnO_(2) structure after arbitrarily doping was larger than that before undoped,and the bond length of the newly formed O-W bond and the O-Sn bond was not much different,and a stable structure was formed after doping.The analysis of energy band and band gap showed that,due to the significant increase in the number of doped energy bands of W element,the conduction band moved down and crosses the Fermi level,resulting in a decrease in the band gap,and a reduction in the distance required to move during the carrier transfer process,which helped the carriers transition.Its unique d orbital not only provided more energy,but also reduced the band gap due to its coupling with O.When the doping ratio was 6.25%,the gap could be reduced to 0.008eV.The bottom of the conduction band and the top of the valence band were approximately coincident in the energy band diagram.The density of states diagrams and atomic charge population reflected the energy distribution of different orbitals after doping.The distribution of the doped density diagrams of different proportions was roughly the same.The introduced W element mainly provided the energy on the 5d orbital,the 5s orbit of Sn and the 5d orbit of W were coupled to widen the orbit.At the same time,the results showed that the binding ability of O-W bond was stronger than that of O-Sn bond.After doping,the total charge increased and the carrier concentration increased.The calculated results of conductivity and differential charge density diagrams directly verified that after doping W,the conductivity of the material was better when the concentration ratio was 6.25%compared to other ratios.After comprehensive comparison,it was determined that when the proportion of W-doped SnO_(2) was 6.25%,the conductivity of SnO_(2) material was the best,and the conductivity was greatly improved compared with that before undoped.Therefore,this paper conducted simulation analysis of electrical performance by doping W element in AgSnO_(2) material.The calculation results provided a theoretical basis for follow-up research.