| Thermoelectric materials is a king of functional materialsachieving thermal energy andelectrical energy directly into each other, mainly used for refrigeration and powergeneration. Thermoelectric devices have no noise, no radiation, no pollution, nomaintenance, long service life and many other advantages, in recent years, thermoelectricmaterials and thermoelectric devices have been extensively studied. Ca3Co4O9is a layeredoxide thermoelectric material, with good structure and chemical stability, andenvironment-friendly, anti-oxidation, suitable for mass production, and is a kind of potentialhigh-temperature thermoelectric materials. ResearchforCa3Co4O9has been focused ondoping, microstructure optimization and compositingwithothermaterials.Doping not onlyreduces the resistivity of Ca3Co4O9but also reduces the Seebeck coefficient, sotheimproving of Ca3Co4O9properties by doping is limited; Microstructure optimization ismainly to obtain textured structure, but the properties of textured Ca3Co4O9are difficulty tocatch up with that of Ca3Co4O9single crystaldue tothe influence of interface betweenCa3Co4O9sheets. Compositingwith silver particlecan also optimize thepropertiesofCa3Co4O9, but the compositing is limitedforthepoor thermoelectric properties of silver.Ca3Co4O9/Bi2Ca3Co2O9composite materials havebeen proposed by ourgroupand some goodpreliminary resultshavebeenobtained, this paper conduct a further study.Firstly, this paper investigatedtheeffects of synthesis method and dopingontheproperties ofCa3Co4O9better Ca3Co4-xCuxO9powder were synthesized by usingsolventmethod, andthenCa3Co4-xCuxO9/Bi2Ca3Co2O9compositeswere obtainedbymixingwith Bi2O3andhot-pressing and annealing.Secondly, microstructure and properties ofthe composites were characterized,andCa3Co4-xCuxO9-Bi2Ca3Co2O9-Ca3Co4-xCuxO9alternating superpositionstructure hasbeenobserved, effects of Cu-doping and Bi2O3addition on the properties of composite werestudied.The maximum output powerofsamplereached110mW (about0.6mW/cm3K), and the largest ZT reached0.49at973K.Finally, the conductive mechanisminas-synthesizedmaterial wereconcluded,which met thepolaron transition conduction mechanismabove600K, and with the increment of Cudoping,the activationenergyofpolaron transition decreased,whilewith the increase ofBi2O3addition,the activation energydecreasedfirstand increased again. |
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