Rare Earth Doped And Properties Of Porous Ca₃Co₄O₉ Thermoelectric Materials

Energy shortages and environmental degradation has become a big problem to the sustainable development for human society.In order to alleviate the energy shortage and reduce environmental pollution,research and development of renewable energy is imminent.With solid internal carrier movement for heat and electricity direct transformation of environmentally friendly thermoelectric conversion technique,as one of the backup mechanisms,which has become one of the frontiers and hotspots in the high-tech fields.Oxide system is one of the most important system in thermoelectric materials.Oxides thermoelectric materials have many advantages,such as good thermoelectric properties,high temperature resistance,oxidation resistance,thermal stability,no pollution,long service life,rich raw materials,low cost and simple preparation,caused the wide attention of scientists.Among them,thermoelectric oxide Ca3Co4O9 electricity and heat transport can be adjusted independently because of its special layered structure.Thus,its thermoelectric properties have good modified space.Ca3Co4O9 have a broad application prospect in thermoelectric power generation device and in the field of refrigeration as well as insufficient research in its thermoelectric performance,this studies focused on the optimization of the thermoelectric properties.La-doped Ca3Co4O9 and porous Ca2.6La0.4Co4O9 were synthesised by steric entrapment method,combined with normal pressure sintering process to prepare block cereamic samples after cold isostatic pressing.The phase composition and microstructure have been characterized.Moreover,the changing characteristics of Seebeck coefficient,electrical resistivity and power factor with La3+and CO(NH2)2 content was studied.Ca3Co4O9 precursor prepared by solid state reaction and steric entrapment method.The results of TG-DSC、SEM and XRD show that steric entrapment method can successfully get pure phase,grain fine powder,and decrease synthesized temperature,and sample’s Seebeck coefficient and power factor is obviously higher than solid state reaction.Smax=179μV/K(976K),increased by 60%;PFmax=7.5×10-4m W/(cm·K2)(976K),increased 16 times;The electrical resistivity is slightly increased.XRD and SEM of La-doped Ca3Co4O9 samples were prepared by steric entrapment method show that the main phase is Ca3Co4O9 after sintering,trace doping doesn’t change phase structure,but it can decrease crystallinity of system and inhibit grain growth.What’s more,La-doped can effectively improve Ca3Co4O9 thermoelectric properties,and it has the certain concentration limit.Which has reached optimal values in La0.4 at 974 K,Smax=186μV/K(974K),ρmin=39.6mΩ·cm,PFmax=8.78×10-4m W/(cm·K2),optimizing 4%,12%,18%,respetively.Ca2.6La0.4Co4O9 precursor powder adding pore-forming agent CO(NH2)2,synthesis series of porous ceramic samples.The SEM results show that pore-forming agent CO(NH2)2 can keep original structure,optimizing structure of the samples and improve thermoelectric properties.Which has reached optimal values in V4 at 974 K,ρmin=16.4mΩ·cm,PFmax=1.84×10-3m W/(cm·K2),optimizing 59%,110%,respetively.