金屬摻雜對於鉍鉭氧化物材料Bi0.77Ta0.23-xMxO1.73-d (M = Mg, Sm, Eu, Zr) 離子導電度影響

Abstract

離子導體可被應用於固態氧化物燃料電池以及氧穿透膜等電化學裝置，其中螢石結構的-Bi2O3因具備高離子導體的特性而在近年來備受矚目，但其結構只穩定於1003到1098K。為了使氧化鉍在室溫也維持高離子導電度的螢石結構，氧化鎂、氧化釤、氧化銪、與氧化鋯分別摻入鉍鉭氧化物並取代氧化鉭。本論文以固態法合成鎂、釤、銪、鋯摻雜鉍鉭氧化物粉末 (Bi0.77Ta0.23-xMxO1.73-; M = Mg, Sm, Eu, Zr)。在X光粉末繞射圖譜中可知鉍鉭氧化物在室溫下為一缺陷的螢石結構，與高溫時的立方相氧化鉍相同。當以鎂、釤、銪、鋯取代部份的氧化鉭時，從X光粉末繞射圖譜中可觀察到四者的摻雜量x可到達0.04。在熱分析的量測結果中可以明顯地發現氧化鉍在1002K時有一從單斜相轉變為立方相的吸熱峰，而在1097K時即到達熔點，其高導電度的立方相結構僅穩定於約100K的範圍內。而在摻雜鉭的三元相以及共摻後的四元相系統中並無觀察到相轉變，根據室溫的X光粉末繞射圖譜結果可推測三元相以及四元相系統在1123K以下可維持一缺陷的螢石結構。接著更進一步，以X射線光電子能譜儀分析摻雜後離子的氧化態與鍵結環境，其結果顯示以鎂、釤、銪、鋯進行共摻並不會改變鉍以及鉭離子的氧化態，而氧離子的束縛能會因較低電負度離子的摻雜而降低，推測此一結果可使氧在晶格中變得更易移動進而增加離子導電度。以密度計以及掃描式電子顯微鏡確認碇材緻密度後，量測材料的離子導電度，總體來說，共摻能夠增加鉍鉭氧化物的氧空缺，有助於提升離子導電度。而鎂在四種離子中能夠最有效地提升離子導電度，其導電度在1023K即可到達0.14 Scm-1，在此溫度下高於已商業化之材料YSZ以及GDC。

Oxide ion conductors have received great interests for numerous application including solid oxide fuel cells, and oxygen transport membranes. The fluorite-related -Bi2O3 exhibits high oxide ion conductivity; however, this phase is only stable in the narrow temperature range of 1003-1098K. In this study, the oxides of MgO, Sm2O3, Eu2O3 and ZrO2 were utilized as co-dopants with Ta2O5 to the Bi2O3 host material, which maintained the fluorite-related structure at room temperature. Bi0.77Ta0.23-xMxO1.73- (M = Mg, Sm, Eu, Zr; x = 0, 0.02, 0.04) was synthesized by solid-state reaction at 1023K. The powder X-ray diffraction patterns confirm that the products retain a -Bi2O3 structure. The effects of the co-dopants on the thermal stability, bonding and ionic conductivity of Bi0.77Ta0.23-xMxO1.73-(M = Mg, Sm, Eu, Zr; x = 0, 0.02, 0.04) were investigated by differential temperature analysis, X-ray photoelectron spectroscopy and AC impedance spectroscopy. The differential temperature analysis reveals the Bi0.77Ta0.23-xMxO1.73-δ (M = Mg, Sm, Eu, Zr; x = 0, 0.02, 0.04) are stable from room temperature to 1123K. The X-ray photoelectron spectroscopy indicates the effect of dopants to oxygen binding energies. The Bi0.77Ta0.19Mg0.04O1.67 exhibits the highest conductivity and followed by the Bi0.77Ta0.21Sm0.02O1.71, Bi0.77Ta0.23Eu0.04O1.7 ceramics with similar values, and Bi0.77Ta0.23Zr0.04O1.71 the third. The Bi0.77Ta0.19Mg0.04O1.67 shows the conductivity of  = 0.14 Scm-1 at 1023K, greater than that of YSZ and GDC under the same temperature.