热压烧结增强Ca3Co4O9多晶的c轴择优织构和电输运性质的研究

分别采用常压固相反应和进一步的真空热压烧结法制备了Ca_3Co_4O_9多晶块材,通过XRD、SEM、致密度、电阻率-温度曲线、霍尔效应测试,对比研究了热压烧结对多晶织构和电输运性质的影响。结果表明两种方法制备的多晶样品均为c轴择优,经热压烧结后多晶的择优织构显著增强,致密度增大,但真空烧结使样品中氧的化学计量比不足,结晶质量略有下降。热压烧结后多晶的面内电阻率显著下降,其室温电阻率约为常压烧结样品的1/7,且电阻率随温度的降低而增大,这主要是由于热压样品晶粒沿(00l)择优排列显著增强,使沿材料ab面内的电输运占优,且晶界和缺陷散射减弱使Co~(4+)载流子迁移率增大。

Enhanced Texture and Electrical Transport Property of c-axis Oriented Ca3Co4O9 Polycrystals by Hot-press Sintering

Ca3Co4O9 polycrystalline bulks were respectively prepared via solid-state reaction sintering in air and further hotpress sintering in vacuum.The influences of hot-press sintering on the texture and electrical transport properties of polycrystals were comparatively studied by the measurements of XRD,SEM,density,temperature dependent resistivity curve and Hall effect.The results showed that the polycrystalline bulks prepared via two different methods were all of c-axis preferred orientation.The c-axis orientation and density were significantly enhanced after hot-press sintering,while the crystallization quality declined slightly owing to oxygen deficiency after sintering in vacuum.The hot-press sintered polycrystal exhibited much lower resistivity which was only oneseventh of pressureless sintered sample's at room temperature,and the resistivity increased with decreasing temperature.This was mainly due to the dominant electrical transportation along the crystal ab-plane and increased Co4+ carrier mobility resulting from the enhanced (00l) preferential texture and less scattering effects at grain boundaries and defects.