Bocher L, Aguirre M H, Logvinovich D, Shkabko A, Robert R, Trottmann M, Weidenkaff A
Empa-Solid State Chemistry and Catalysis, Ueberlandstrasse 129, Duebendorf CH-8600, Switzerland.
Inorg Chem. 2008 Sep 15;47(18):8077-85. doi: 10.1021/ic800463s. Epub 2008 Aug 13.
Perovskite-type CaMn(1-x)Nb(x)O(3+/-delta) (x = 0.02, 0.05, and 0.08) compounds were synthesized by applying both a "chimie douce" (SC) synthesis and a classical solid state reaction (SSR) method. The crystallographic parameters of the resulting phases were determined from X-ray, electron, and neutron diffraction data. The manganese oxidations states (Mn(4+)/Mn(3+)) were investigated by X-ray photoemission spectroscopy. The orthorhombic CaMn(1-x)Nb(x)O(3+/-delta) (x = 0.02, 0.05, and 0.08) phases were studied in terms of their high-temperature thermoelectric properties (Seebeck coefficient, electrical resistivity, and thermal conductivity). Differences in electrical transport and thermal properties can be correlated with different microstructures obtained by the two synthesis methods. In the high-temperature range, the electron-doped manganate phases exhibit large absolute Seebeck coefficient and low electrical resistivity values, resulting in a high power factor, PF (e.g., for x = 0.05, S(1000K) = -180 microV K(-1), rho(1000K) = 16.8 mohms cm, and PF > 1.90 x 10(-4) W m(-1) K(-2) for 450 K < T < 1070 K). Furthermore, lower thermal conductivity values are achieved for the SC-derived phases (kappa < 1 W m(-1) K(-1)) compared to the SSR compounds. High power factors combined with low thermal conductivity (leading to ZT values > 0.3) make these phases the best perovskitic candidates as n-type polycrystalline thermoelectric materials operating in air at high temperatures.
通过应用“温和化学”（SC）合成法和经典固态反应（SSR）法合成了钙钛矿型CaMn(1-x)Nb(x)O(3±δ)（x = 0.02、0.05和0.08）化合物。根据X射线、电子和中子衍射数据确定了所得相的晶体学参数。通过X射线光电子能谱研究了锰的氧化态（Mn(4+)/Mn(3+)）。研究了正交晶系CaMn(1-x)Nb(x)O(3±δ)（x = 0.02、0.05和0.08）相的高温热电性能（塞贝克系数、电阻率和热导率）。两种合成方法得到的不同微观结构与电输运和热性能的差异相关。在高温范围内，电子掺杂的锰酸盐相表现出较大的绝对塞贝克系数和较低的电阻率值，从而导致高功率因子PF（例如，对于x = 0.05，S(1000K) = -180 μV K(-1)，ρ(1000K) = 16.8 mΩ·cm，并且在450 K < T < 1070 K时PF > 1.90×10(-4) W m(-1) K(-2)）。此外，与SSR化合物相比，SC衍生相的热导率值更低（κ < 1 W m(-1) K(-1)）。高功率因子与低导热率相结合（导致ZT值 > 0.3）使这些相成为在空气中高温运行的n型多晶热电材料的最佳钙钛矿候选物。
