不同元素掺杂对CaTiO_(3)微观结构及热电性能的影响

Effects of Different Element Doping on Microstructure and Thermoelectric Properties of CaTiO_(3)

CaTiO_(3)是一种新兴的高温氧化物热电材料,但多种元素掺杂对其微观结构与热电性能的影响规律尚不清晰。本研究采用水热法结合真空热压烧结分别制备了Cr、Nb、Eu、Dy、Ce与La六种不同元素掺杂的CaTiO_(3)多晶块体样品。Cr掺杂导致大量纳米级Cr相析出,由于基体中施主元素含量过低,功率因子严重损失,其ZT仅为0.012(983 K)。Eu掺杂并未为基体提供施主载流子,导致ZT提升不明显,仅为0.141(1031 K)。Nb掺杂导致高热导的微米级Nb相析出,热导率上升,但基体中Nb含量较多为基体提供了载流子,使其ZT有明显改善,达到0.263(1013 K)。Dy、Ce与La掺杂则既提供载流子又作为点缺陷散射声子,既提高了功率因子又降低了晶格热导率,极大地提升了热电性能,ZT在1031 K分别达到0.357、0.398、0.329,比纯CaTiO_(3)(0.096)分别提升了296%、342%、265%。其中,Dy掺杂的样品在整个温度测试范围内具有最低的晶格热导率和较高的功率因子,通过调控Dy含量与晶界处富集第二相的含量,可以解耦电和热传输性能,有望刷新目前CaTiO_(3)的ZT记录。本研究揭示了多种元素掺杂条件下CaTiO_(3)的成分-结构-性能联系,为其在高温热电领域的应用提供了理论支撑。

Despite the growing research in CaTiO_(3)as a novel high-temperature oxide thermoelectric material,effects of various elements doping on the microstructure and thermoelectric performance of CaTiO_(3)have not been fully understood.Here,a combination of hydrothermal synthesis and vacuum hot-press sintering techniques was employed to fabricate polycrystalline bulks of CaTiO_(3)doped with six elements:Cr,Nb,Eu,Dy,Ce,and La.Cr doping resulted in substantial precipitation of nanoscale Cr phases,leading to a severely compromised power factor and a ZT of only 0.012 at 983 K due to insufficient donor element concentration in the matrix.Incorporating Eu as adonor carrier in the matrix is proved ineffective,resulting in a marginal ZT enhancement of 0.141 at 1031 K.Nbdoping resulted in the formation of micrometer-scale Nb phases with high thermal conductivity,leading to anelevation in thermal conductivity.However,the relatively higher Nb concentration in the matrix provided carriers,resulting in a noticeable ZT improvement to 0.263 at 1013 K.On the contrary,Dy,Ce,and La doping exhibitedremarkable dual functionality as donor dopants and point defects,thereby significantly enhancing the power factorand concurrently reducing the lattice thermal conductivity.These improvements were achieved through efficientmanipulation of carrier concentration and implementation of phonon scattering.As a result,the thermoelectricfigure of merit(ZT)reached 0.357,0.398,and 0.329 at 1031 K for Dy,Ce,and La-doped CaTiO_(3)bulks,respectively.These values represent an extraordinary improvement of 296%,342%,and 265%,respectively,as compared to thatof the pristine CaTiO_(3)(0.096@1031 K).Notably,Dy-doped samples exhibited significantly reduced lattice thermalconductivity and comparatively higher power factors over the entire temperature range.Regulating Dy content andenhancing the second phase at grain boundaries enabled the decoupling of electrical and thermal transportproperties,potentially surpassing the current ZT record of CaTiO_(3).This study provides valuable insights into therelationships among composition,structure,and performance in CaTiO_(3)doped with various elements,offeringtheoretical support for high-temperature thermoelectric applications.