High-temperature thermoelectric properties of Ln(Co, Ni)O 3 (Ln = La, Pr, Nd, Sm, Gd and Dy) compounds (original) (raw)
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High-temperature thermoelectric properties of Ca1−xPrxMnO3−δ (0⩽x<1)
Physica. B, Condensed matter, 2004
Ca 1Àx Pr x MnO 3Àd (x=0, 0.05, 0.15, 0.1, 0.2, 0.4, 0.67; d=0.02) samples were prepared by a solid-state reaction method. X-ray diffraction analysis showed that all samples prepared were of single phase with orthorhombic structure. Electrical resistivity measurements from room temperature to 1300 K showed that a metallic conducting tendency dominated at high temperatures. The hopping nature of the charge carriers was well interpreted in the framework of polaron theory. The Seebeck coefficient was measured in the same temperature interval, and its concentration dependence was analyzed using the high-temperature (HT) thermopower theory proposed by Marsh-Parris. The thermal conductivity and the figure of merit of the prepared samples were also compared with those of other similar perovskite compounds. The observed figure of merit of the sample with x=0.15 was Z=1.5 Â 10 À4 K À1 at T=1100 K, indicating a good potential for application as a HT thermoelectric material.
Thermoelectric Properties of Ca3Co2−xMnxO6 (x = 0.05, 0.2, 0.5, 0.75, and 1)
Materials, 2019
High-temperature instability of the Ca 3 Co 4−y O 9+δ and CaMnO 3−δ direct p-n junction causing the formation of Ca 3 Co 2−x Mn x O 6 has motivated the investigation of the thermoelectric performance of this intermediate phase. Here, the thermoelectric properties comprising Seebeck coefficient, electrical conductivity, and thermal conductivity of Ca 3 Co 2−x Mn x O 6 with x = 0.05, 0.2, 0.5, 0.75, and 1 are reported. Powders of the materials were synthesized by the solid-state method, followed by conventional sintering. The material Ca 3 CoMnO 6 (x = 1) demonstrated a large positive Seebeck coefficient of 668 µV/K at 900 • C, but very low electrical conductivity. Materials with compositions with x < 1 had lower Seebeck coefficients and higher electrical conductivity, consistent with small polaron hopping with an activation energy for mobility of 44 ± 6 kJ/mol and where both the concentration and mobility of hole charge carriers were proportional to 1−x. The conductivity reached about 11 S•cm −1 at 900 • C for x = 0.05. The material Ca 3 Co 1.8 Mn 0.2 O 6 (x = 0.2) yielded a maximum zT of 0.021 at 900 • C. While this value in itself is not high, the thermodynamic stability and self-assembly of Ca 3 Co 2−x Mn x O 6 layers between Ca 3 Co 4−y O 9+δ and CaMnO 3−δ open for new geometries and designs of oxide-based thermoelectric generators.
Inorganic Chemistry, 2008
Perovskite-type CaMn 1-x Nb x O 3(δ (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(δ (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 µV K-1 , F 1000K) 16.8 mΩ cm, and PF > 1.90 × 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 (κ < 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.
Ceramics International, 2018
CaMnO 3-based materials are very attractive among n-type thermoelectric oxides for high-temperature applications when they are appropriately doped. The main drawback of these materials is the cost associated to the necessary rare earth cations. This work aims decreasing the amount of these materials through a partial substitution of Ca 2+ by an equimolar mixture of K + and Yb 3+ , Ca 1-x (K 0.5 Yb 0.5) x MnO 3 , with x = 0.05, 0.10, 0.15, and 0.20. XRD studies have confirmed that the thermoelectric phase is the major one in all samples. Microstructure has shown the formation of large crystals, and an increasing porosity when the substitution is raised. This evolution has been confirmed through density measurements. Electrical resistivity has been drastically decreased for the 0.10 substituted samples, compared with the 0.05 ones, slightly increasing for higher substitution. On the other hand, absolute Seebeck coefficient and thermal conductivity are lower when the substitution is raised. The best ZT values have been achieved for the 0.10 substituted samples, which are around the typical reported in the literature for higher doping level. These results clearly point out to a decrease of the necessary rare earth dopant content to achieve similar performances in CaMnO 3 ceramics, which is of the main economic significance for their industrial production.
Journal of Electronic Materials, 2009
We have investigated the effects of Bi doping on the crystal structure and high-temperature thermoelectric properties of the n-type layered oxide Ca 2 MnO 4Àc . The electrical conductivity r and the absolute value of the Seebeck coefficient S were, respectively, found to increase and decrease with Bi doping. The thermal conductivity j of doped Ca 2 MnO 4Àc is relatively low, 0.5 W/m K to 1.8 W/m K (27°C to 827°C). Consequently, the ZT value, ZT = rS 2 T/j, increases with Bi doping. The maximum ZT is 0.023 for Ca 1.6 Bi 0.18 MnO 4Àc at 877°C, which is ten times higher than that of the end member, Ca 2 MnO 4Àc . The increase of ZT mainly results from the considerable increase of r, which can be explained in terms of structural change. The Mn-O(1) and the Mn-O(2) distances in the c-direction and ab-plane, respectively, increase with increasing Bi concentration, indicating that the valence state of Mn ions decreases with the increase of electron carriers in the CaMnO 3 layers. In addition, the Mn-O(2)-Mn bond angle increases linearly with Bi doping, leading to an improvement of the electron carrier mobility.
High temperature thermoelectric properties of double-filled InxYbyCo4Sb12 skutterudites
Journal of Applied Physics, 2009
CaMnO 3−δ with complex additives Bi 2 O 3 -V 2 O 5 were prepared by the solid-state reaction. The crystal structures of the Ca 1−x Bi x Mn 1−y V y O 3−δ (0 ≤ x = y ≤ 0.08) solid solutions were determined by means of the powder X-ray diffraction (XRD) using Rietan 2000 program and the high temperature thermoelectric properties were also investigated. Perovskite-type Ca 1−x Bi x Mn 1−y V y O 3−δ solid solutions are n-type semiconductors. The lattice parameters increase with increasing dopant level. The high temperature thermoelectric properties are improved due to Bi 2 O 3 -V 2 O 5 simultaneous doping. A maximum ZT value reaches to 0.21 for electron-doped Ca 0.96 Bi 0.04 Mn 0.96 V 0.04 O 3−δ at 1050 K, which is about twice as high as that of CaMnO 3−δ . The thermal shock resistance at temperatures between 20 and 450 • C is also highly improved.
Processing effects on the thermoelectric properties of Bi2Ca2Co1.7Ox ceramics
2014
Bi 2 Ca 2 Co 1.7 O x bulk polycrystalline ceramics were prepared by the solid state method and by directional growth. Moreover, the effect of annealing on the textured materials has been studied. Microstructure has shown randomly oriented grains in the classical sintered materials while in the textured samples they were well oriented with their c-axis nearly perpendicular to the growth direction. Furthermore, the annealed samples showed much lower amount of secondary phases than the as-grown ones. These microstructural changes are reflected on the thermoelectric properties which increase with the grain orientation and with the decrease on the secondary phases content mainly due to the electrical resistivity reduction. As a consequence, a raise on the power factor of about 6 and 9 times, compared with the classically sintered samples, was obtained for the as-grown and annealed samples, respectively. The maximum power factor obtained at 650 ºC in the annealed samples (~ 0.31 mW/K 2 m) is about 50 % higher than the obtained in sinter-forged textured materials at the same temperature.
Journal of Materials Science
A two-step synthesis approach was utilized to grow CaMnO 3 on M-, R-and C-plane sapphire substrates. Radio-frequency reactive magnetron sputtering was used to grow rock-salt-structured (Ca, Mn)O followed by a 3-h annealing step at 800°C in oxygen flow to form the distorted perovskite phase CaMnO 3. The effect of temperature in the post-annealing step was investigated using x-ray diffraction. The phase transformation to CaMnO 3 started at 450°C and was completed at 550°C. Films grown on R-and C-plane sapphire showed similar structure with a mixed orientation, whereas the film grown on M-plane sapphire was epitaxially grown with an out-of-plane orientation in the [202] direction. The thermoelectric characterization showed that the film grown on M-plane sapphire has about 3.5 times lower resistivity compared to the other films with a resistivity of 0.077 Xcm at 500°C. The difference in resistivity is a result from difference in crystal structure, single orientation for M-plane sapphire compared to mixed for R-and C-plane sapphire. The highest absolute Seebeck coefficient value is-350 lV K-1 for all films and is decreasing with temperature.
Materials Chemistry and Physics, 2022
Electric resistivity, thermoelectric power and thermal conductivity of a polycrystalline sample of the composite crystal [Ca 2 CoO 3.34 ] 0.614 [CoO 2 ], also known as Ca 3 Co 4 O 9 , have been measured below 300 K. Metallic conductivity accompanied by large thermoelectric power has been observed down to 50 K. At 300 K, the sample exhibits a thermoelectric power of S = 133 µV•K −1 , resistivity of ρ = 15 m •cm and thermal conductivity of κ = 9.8 mW•K −1 •cm −1. The resulting dimensionless figure of merit becomes Z T 300 = 3.5×10 −2 , which is comparable to the value reported for a polycrystalline sample of NaCo 2 O 4 , indicating that the title compound is a potential candidate for a thermoelectric material.