第二相金属纳米颗粒掺杂对SrTiO3体系热电性能的调控研究

The RxSr1-xTiO3(R=La,Nd, etc.) oxides with the perovskite structure exhibit n-type metallic conductivity, high Seebeck coefficient, and large power factor, which present great potential applications in thermoelectric conversion devices. However, due to the large lattice thermal conductivity, these oxides exhibit poor thermoelectric performance and thus there is a certain distance away from their practical applications. In the current project, the RxSr1-xTiO3(R=La,Nd, etc)systems are selected as the matrix phase, and the metallic nanoparticles M(=Ag, Au and Pt) as the secondary phase. Via the nanoinclusion of the metallic nanoparticles into the matrix phase, the M/RxSr1-xTiO3 nanocomposites are synthesized. In these nanocomposites, due to the different chemical potential between the RxSr1-xTiO3 matrix phase and the secondary metallic nanoparticles,there will be the interfacial potentials between these two phases.On the one hand, the phonon scattering is enhanced and thus the thermal conductivity is weakened correspondingly. On the other hand, such interfacial potentials cause energy-dependent scattering of electrons, leading to an energy filtering effect, which increases the Seebeck coefficient. As a result, the thermoelectric properties of the RxSr1-xTiO3 systems will be improved. By changing the composition, the size, the content of the secondary metallic nanoparticles and the content and the carrier density of the matrix phase RxSr1-xTiO3, we will systematically investigate the thermoelectric properties of the M/RxSr1-xTiO3 nanocomposite. Based on these results of our current project, it is expected that the electron-phonon transport characteristic of the SrTiO3 systems will be probed, and that the reliable experiment foundations about improving the thermeoelectric properties of such systems are then provided.

n型-钙钛矿结构氧化物RxSr1-xTiO3(R=La,Nd等)具有金属导电性,高热电势和大热电功率因子, 作为热电转换材料具有很好的潜在应用价值。然而，该体系较大的晶格热导率导致其热电性能偏低。本项目选取n型-RxSr1-xTiO3为基体相，通过第二相金属纳米颗粒M(M=Ag、Au、Pt)掺杂，合成M/RxSr1-xTiO3纳米复合体系。掺杂的第二相金属纳米颗粒不但加强声子散射降低体系热导率，而且基底相和第二相金属纳米颗粒之间的化学势差异会在两者界面处形成一个界面势垒，该势垒对载流子进行能量过滤和选择性散射而提升热电势，最终达到改善体系热电性能的目的。本项目研究并揭示第二相金属纳米颗粒的种类、颗粒度及含量对体系热电性能的影响，及基体相成分及其载流子浓度变化时，体系热电性能随第二相金属纳米颗粒掺杂的变化规律。揭示复合体系中电声子输运特点，为提高SrTiO3体系氧化物材料的热电性能奠定基础。

n型-钙钛矿结构氧化物R1-xSrxTiO3（R=La,Nd）具有金属导电性，高热电势和大热电功率因子，作为热电材料转换具有很好的潜在应用价值。然而，该体系较大的晶格热导率导致其热电性能偏低。通过第二相金属纳米颗粒Ag等的掺杂，合成Ag/ R1-xSrxTiO3纳米复合体系。引入第二相金属纳米颗粒不但加强声子散射降低体系热导率，而且R1-xSrxTiO3和第二相金属纳米颗粒之间的化学势差异会在界面处形成一个界面势垒，该势垒可以对载流子进行能量过滤和选择性散射而提升热电势，最终达到改善体系热电性能的目的。.在该项目的资助下，完成的主要研究结果如下。.1、 Ag/Sr0.9La0.1TiO3复合物的热电性质的研究.通过水热和高温烧结（1450度）的方法制备得到Sr0.9La0.1TiO3/xAg (x=0,0.05,0.10 和0.15）复合物。随着Ag的添加，虽然体系在整个测量温度范围内表现为绝缘行为，但是电导率还是增大的，这是因为Ag的加入增加了体系的电子数目。同时，由于载流子浓度的增加以及低能电子的能量反转效应（energy filter effect)，体系的Seebeck系数S也随着Ag含量的增加先增大而后减小。功率因子PF=S2，随着温度的增加，先增大到一个最大值而后减小。体系的热导率κ随着温度的升高而降低。因此，按照公式ZT=PT/κ, 随着Ag的添加，整个ZT值是增大的，即，由x=0的时候的0.09增加到0.15时的0.20。说明，Ag的加入使体系的电导率增加，热导率减小，Seebeck系数增加，因此整个ZT值随着Ag含量的增加而增大。.2、 Ag/(Sr0.9La0.1)3Ti2O7复合物的热电性质的研究.在前面Ag添加113-SrTiO3的基础上，采用相同的制备方法，我们研究了Ag添加327结构的(Sr0.9La0.1)3Ti2O7热电性质。结果发现，(Sr0.9La0.1)3Ti2O7的热电性能也随着Ag的添加增大，即，由x=0的时候的0.04增加到0.10时的0.12。.3、研究发现在高温烧结的过程中Ag特别容易析出。所以，Ag的含量严格来说不是准确的计量比。其余的金属粒子掺杂也出现同样的情况。