Papers by Keyword: Ca₃Co₄O₉

Abstract: Polycrystalline Ca_3-xBi_xCo₄O₉ samples have been prepared by solid-phase reaction followed by spark plasma sintering process. The thermoelectric properties have been systematically investigated from room temperature to near 1000K. It is found that the change of the carrier concentration leads to the change of resistivity, which is mainly associated with doping induced point defect phonon scattering. The change of the thermal potential mainly comes from the spin entropy. In addition, polycrystalline Ca_3-xBi_xCo₄O₉ had a maximum figure of merit of 0.30 at 973 K, which was about 50% higher than Ca₃Co₄O₉. It indicated that doping approach can effectively improve the thermoelectric performance of Ca₃Co₄O_9+δ-based material.

Abstract: Ca₃Co_4xCu_xO₉ (0x1.4) misfit-layered thermoelectric oxides were prepared by traditional solid-state reaction method which cost less, operate easer, may produce Ca₃Co₄O₉ on large scale. XRD study shows that we obtain Ca₃Co₄O₉ major phase in series Ca₃Co_4xCu_xO₉ (0x1.4) samples which were sintered at the highest temperature 880°C for 8h by two steps. Metallographic microscopic analysis indicates that some samples grain size range at 2~4μm which were doped less Cu. Doping Cu in different way experiment suggests that Ca₃Co_4xCu_xO₉ (x=0.4) sample has lower electric resistivity while Ca₃Co₄O₉+5%Cu samples resistivity increases, compared with Ca₃Co₄O₉ (x=0). The article infers that Ca₃Co_4xCu_xO₉ (0x0.4) can decrease the electric resistivity of Ca₃Co₄O₉.

Abstract: Micro-sized Ca₃Co₄O₉ powder was prepared by solid phase method at 850-950°C in air atmosphere. Seebeck effect of carbon fiber reinforced cement composites was enhanced efficiently by combining the Ca₃Co₄O₉ powder of 3.0wt.% by mass of cement. The absolute thermoelectric power achieves 1.65 fold increase and is up to 58.6μV/°C at room temperature. The lower activation energy of holes carriers and higher carrier concentration by doping Ca₃Co₄O₉, are probably attributed to the increase of absolute thermoelectric power.

Abstract: Ca₃Co₄O₉ powders were synthesized by a solid-state reaction method. Porous Ca₃Co₄O₉ ceramics with parallel sheet shaped pores were prepared by a template sacrifice method using epispastic polystyrend (EPS) hollow spheres as the templates. During compaction of the green body, the EPS hollow spheres change into EPS discs due to the pressing force. After sintering, the pores in the Ca₃Co₄O₉ ceramics are sheet shaped, well distributed and parallel to the pressing surface of compaction. The value of ZT merit of the porous Ca₃Co₄O₉ sample obtained with 10 wt% EPS spheres is 0.0489. It was found that the ZT merit value can be improved by changing the density of sample to achieve a high ratio of electrical conductivity to thermal conductivity.

Abstract: Thermoelectric ceramic targets of Ca₃Co₄O₉ and Ca₃Co₂O₆ were prepared by the sol-gel method. The technology and mechanism of synthesizing the thermoelectric thin films of Ca₃Co₄O₉ and Ca₃Co₂O₆ were investigated. The thin films of Ca₃Co₄O₉ and Ca₃Co₂O₆ were grown on (0001)-oriented (c-cut) Al₂O₃ substrates by pulsed-laser deposition techniques (PLD). Ca₃Co₄O₉ thin films grown at substrate temperature of 700°C and 800 °C appear to be obviously c-axis-oriented. But the x-ray diffraction peak of Ca₃Co₂O₆ thin films was not confirmed. Ca₃Co₄O₉ thin films and Ca₃Co₂O₆ thin films exhibited Ca elements and Co elements volatilization at high temperatures.

Abstract: (Ca1-xAx)3Co4O9 (A: Sr, Ba) composition-spread films were fabricated successfully on TiO2 (100) substrate by combinatorial pulsed laser deposition (CPLD), and their thermoelectric (TE) properties and structure were evaluated by the multi-channel thermoelectric measurement system and concurrent X-ray analysis respectively. The largest power factor in (Ca1-xSrx)3Co4O9 film library was achieved as 1.67µW/cmK2. The influence of substitution on TE properties was investigated by doping Sr2+ and Ba2+ ions into Ca3Co4O9. However, there was little change of Seebeck coefficient in the range of 0≤x≤0.1 for (Ca1-xAx)3Co4O9 (A: Sr, Ba) films, which suggested that the substitution ions with smaller size were potential candidates for good TE properties.

Abstract: A series of (Ca0.9Gd0.1)3Co4O9/xAg(x=0, 0.1, 0.15, 0.2) ceramics were prepared by a polyacrylamide gel method and Spark Plasma Sintering. Scanning electron microscopy (SEM) revealed that small size Ag particles were dispersed into the (Ca0.9Gd0.1)3Co4O9(CGCO) matrix. The electrical conductivity of the composites was obviously higher than that of (Ca0.9Gd0.1)3Co4O9, and increased with increase of Ag content. However, the addition of Ag seemed to have a negative impact on the Seebeck coefficient (S) of the composites samples due to its poor S. Since the increase of electrical conductivity (σ) is more significant than the degradation of S, the power factor (P=σS2) was found to be improved by the addition of Ag. At 973 K, the P value of the sample with x =0.2 reached 3.17×10-4 W•m-1•K-2, which was 12.5% higher than that of Ca3Co4O9(CCO) bulk material.