Ca3Co4O9热电材料及其Ca位掺杂改性

氧化物热电材料Ca3Co4O9与传统热电材料相比具有其独特优势,因而引起了广泛的关注.评述了Ca3Co4O9热电材料的主要结构、热电特性及其Ca位掺杂研究的进展(掺入Na,Bi,Ag等),并对Ca3Co4O9热电材料的应用前景进行了展望.     

钴酸盐类氧化物热电材料的研究进展

氧化物热电材料是半导体热电材料中的一种,具有独特的优点和广阔的应用前景,介绍与其研究相关的基础理论,并讨论了改善热电性能的途径.钴酸盐类氧化物中的NaCo2O4、Ca3Co4O9和Ca3Co2O6处于氧化物热电材料的研究前沿,综述了它们的晶体结构、制备方法、元素掺杂、热电性能及影响因素,探讨了其进一步的发展方向.     

Hiah temoerature thermoelectric oerformance of Ce dooed Ca3Co4o9

利用二次固相反应方法制备了Ce掺杂的Ca3Co4O9热电材料（CexCa3-xCo4O9,x=0、0.1、0.3）,并测试了样品的微观结构和高温热电性能。测试结果表明,Ce替代Ca可有效调制Ca3Co4O9的热电参数;随着温度的升高,样品的电阻率和热导率降低,See-beck系数增大。在973K的温度下,Ce0.1Ca2.9Co4O9具有最高的热电性能（ZT=0.23）。     

Ce掺杂Ca3Co4O9的高温热电性能

利用二次固相反应方法制备了Ce掺杂的Ca3Co4O9热电材料(CexCa3-xCo4O9,x=0、0.1、0.3),并测试了样品的微观结构和高温热电性能。测试结果表明,Ce替代Ca可有效调制Ca3Co4O9的热电参数;随着温度的升高,样品的电阻率和热导率降低,See-beck系数增大。在973K的温度下,Ce0.1Ca2.9Co4O9具有最高的热电性能(ZT=0.23)。     

Ca3Co4O9的电子结构、化学键及热电性能

Ca3Co4O9是一类很有希望的新型氧化物热电材料,用离散变分密度泛函方法(DFT-DVM)计算了失配层钴酸盐Ca3Co4O9的电子结构和化学键,讨论了它们与热电性能之间的关系.结果表明,Ca3Co4O9属于窄带半导体,在费米能级附近Co 3d主要对导带贡献,O 2p主要对价带贡献.Ca2CoO3层中Co-O键表现出明显的各向异性特征,在c轴方向上化学键比ab-面方向上强.Ca连接了CoO2和Ca2CoO3层的相互作用,Ca与周围O原子的弱结合有可能导致材料的低热导率.     

钴酸盐热电材料研究进展

热电材料具有重要而广阔的应用前景。氧化物热电材料可以避免传统热电材料的一些缺点而倍受重视。本文综述了NaCo2O4、Ca3Co4O9和Ca3Co2o6等系列的晶体结构、制备方法、元素掺杂与改性、电子结构计算与理论分析等．并探讨了钴酸盐热电材料的进一步发展方向。     

钴酸盐热电材料研究进展

热电材料具有重要而广阔的应用前景.氧化物热电材料可以避免传统热电材料的一些缺点而倍受重视.本文综述了NaCo2O4、Ca3Co4O9和Ca3Co2O6等系列的晶体结构、制备方法、元素掺杂与改性、电子结构计算与理论分析等,并探讨了钴酸盐热电材料的进一步发展方向.     

不同环境下烧结的Ca3Co4O9的热电性能

采用传统的固相反应法在不同的氧压下烧结制得Ca3Co4O9样品,并对其进行了结构和热电性能表征.经研究发现,在氧气环境下烧结样品可以抑制Ca3Co4O9在高温下分解,提高其烧结温度.在氧气环境中烧结的样品成相优于在空气中烧结的样品.一定氧压下烧结样品的电阻率比常压下烧结样品的电阻率大,但是Seebeck系数明显提高,因而改善了Ca3Co4O9的热电性能.     

钴基氧化物热电材料掺杂研究进展

氧化物热电材料是近年研究的热点之一,钴氧化物因具有优良的高温稳定性、抗氧化性、低成本和易于大规模生产等优点而受到人们的广泛关注,被认为是很有使用价值的热电材料,很多学者在此方面进行了大量的研究。详细介绍了元素掺杂对热电性能的影响,从物理机制上分析了掺杂元素的半径和价态对Ca3Co4O9和NaxCo2O4热电性能的影响,为热电材料的进一步研究提供了依据。     

Ca3Co2O6氧化物热电材料的研究现状与进展

介绍了Ca3CO2O6基氧化物热电材料的国内外研究现状、结构特征及应用前景,详细综述了提高Ca3CO2O8基氧化物热电性能的主要途径,包括制备工艺的改进、掺杂改性的研究等,着重从Ca位掺杂和Co位掺杂两方面介绍了Ca3CO2O6在掺杂改性方面的研究进展,并提出了该材料当前存在的问题和今后的发展方向.     

Microstructure and Thermoelectric Properties of Bi- and Cu-Substituted Ca3Co4O9 Oxides

Bi- and Cu-substituted Ca3Co4O9 samples were prepared by conventional solid-state reaction method and the effect of element substitution on the microstructures and thermoelectric properties was investigated. Partial substitution of Cu for Co leads to an increase in electrical conductivity and a decrease in Seebeck coefficient due to the rise of hole concentration. The microstructure of Cu-substituted sample is almost unchanged compared with undoped Ca3Co4O9. On the other hand, partial substitution of Bi for Ca gives rise to a significant increase in the grain size, and c-axis-oriented structure can be formed in Ca2.7Bi0.3Co4O9, resulting in an obvious increase in electrical conductivity. Cu and Bi co-substitution further increases the grain growth and the electrical conductivity of Ca2.7Bi0.3Co3.7Cu0.3O9. Thus, Cu and Bi co-substitution samples possess the optimal thermoelectric performance at high temperature and the highest value of power factor can reach 3.1×10-4 Wm-1·K-2 at 1000 K.     

Improvement in high-temperature thermoelectric properties by adding Mn for Co in Ca3Co4O9

Nano-sized Ca3Co(4-x)Mn(x)O9 (0 < or = x < or = 0.6) thermoelectric powders were synthesized by solution combustion method, using aspartic acid as fuel. The microstructure and high-temperature (500-800 degrees C) thermoelectric properties of the Ca3Co(4-x)Mn(x)O9 were investigated. The addition of Mn for Co in Ca3Co(4-x)Mn(x)O9 resulted in a decrease of the electrical conductivity and a significant increase of the Seebeck coefficient. Consequently, the power factor was remarkably enhanced by the addition of Mn. Ca3Co(3.7)Mn(0.3)O9 sample showed the highest value of the power factor (1.24 x 10(-4) Wm(-1) K(-2)) at 800 degrees C. We believe that the Ca3Co(4-x)Mn(x)O9 is strongly desirable as a novel high-temperature thermoelectric material for power generation.     

EDTA络合溶胶-凝胶法制备Ca3Co4O9粉体

钴基氧化物Ca3Co4O9是一种新型的中高温热电材料。本文以金属醋酸盐和乙二胺四乙酸(EDTA)为原料,利用EDTA络合溶胶-凝胶法制备了Ca3Co4O9粉体,通过X射线衍射(XRD)、热重-差示扫描量热分析(TG-DSC)、傅利叶变换红外光谱(FT-IR)、X射线能谱仪(EDX)和扫描电子显微镜(SEM)等手段对Ca3Co4O9进行表征。实验结果表明,干凝胶在700-900℃条件下恒温煅烧2h,即可获得纯相Ca3Co4O9片状晶体,其晶粒尺寸约为1-2μm。     

N型铌钴氧化物热电材料的合成和热电性能的研究

研究了用热压烧结的方法合成Co4Nb2O9和Co0．66Nb1.33O4，并通过常见的检测和分析方法研究了他们的热电性能和微观结构。研究表明Co0.66Nb1.31O4是一种很有希望的n型热电材料.     

Bi／Bi2O3晶格复合热电薄膜的制备及其性能研究

利用射频磁控溅射法在玻璃基片上制备Bi／Bi2O3晶格复合热电薄膜,考察了溅射功率对单层Bi薄膜表面粗糙度和热电性能的影响,结果表明,当溅射功率为22W时,薄膜具有最小的表面粗糙度16.3nm,电导率和功率因子分别为2．9×10^4S／m和5．74μV／k^2m,单层Bi薄膜最佳的工作温度为85～105℃。Bi／Bi2O3晶格复合热电薄膜最佳的溅射层数为5层,其电导率和功率因子分别为9．0×10^4S／m和21．0μN／k^2m,分别比单层Bi薄膜提高了2．1倍和2．65倍。     

Structural and thermoelectric properties of HfNiSn half-Heusler thin films

The bulk thermoelectric properties of half-Heusler alloys have recently been extensively studied due to their potential as thermoelectric materials. However, only a few publications have been addressed on thin film systems. The present study investigated the structural and thermoelectric properties of HfNiSn half-Heusler alloy thin films grown at different substrate temperatures: 25 °C, 200 °C, and 400 °C. The crystalline phase and structural variation of the films were determined by X-ray diffraction and scanning electron microscopy. Polycrystalline thin films were obtained for utilizing lower substrate temperatures. The HfNiSn thin films exhibited preferred (111) orientation when substrate temperature was higher than 400 °C. The in-plane Seebeck coefficient and resistivity of HfNiSn thin films with preferred orientation were much lower than those of films without orientation. This implies the thermoelectric properties of HfNiSn alloy may exhibit anisotropic characteristics. The best Seebeck coefficient and power factor of HfNiSn thin films obtained in this work are −68 μV/K and 1.3 μW/K²cm, respectively, measured at room temperature. The effects of partial substitution of Sn by Sb on thermoelectric properties of HfNiSn thin films were also studied with a “pseudo-combinatorial” approach.     

La0.67Ca0.33MnO3/YBa2Cu4O8/La0.67Ca0.33MnO3三层膜的时间效应研究

报导了La0.67Ca0.33MnO3/YBa2Cu4O8/La0.67Ca0.33MnO3薄膜中超导特性的时间效应.样品在空气中存放11个月后,超导转变温度都降低,而且每个系列样品的临界厚度增加.对用La0.67Ca0.33MnO3作保护层的YBa2Cu4O8薄膜进行时间效应测量,结果表明当La0.67Ca0.33MnO3层的厚度大于40nm时可以防止水对YBa2Cu4O8薄膜的影响.     

Atomic-resolution imaging of spin-state superlattices in nanopockets within cobaltite thin films

Certain cobalt oxides are known to exhibit ordered Co spin states, as determined from macroscopic techniques. Here we report real-space atomic-resolution imaging of Co spin-state ordering in nanopockets of La(0.5)Sr(0.5)CoO(3-δ) thin films. Unlike the bulk material, where no Co spin-state ordering is found, thin films present a strain-induced domain structure due to oxygen vacancy ordering, inside of which some nanometer sized domains show high-spin Co ions in the planes containing O vacancies and low-spin Co ions in the stoichiometric planes. First-principles calculations provide support for this interpretation.