利用實驗與計算解釋三價離子參雜於電解質BaZrO3的導電趨勢

Abstract

利用實驗與計算研究不同三價參雜金屬於BaZr0.9M0.1O3-α (M3+ = Al 、Ga 、In、Er、Y、Ho、Dy、Gd、Sm、Nd、La)導電率。 實驗部分利用溶膠-凝膠法(sol-gel)合成粉末並燒結於1150℃下5小時再使用XRD、SEM 與EDS進行特性鑑定分析。BaZr0.9M0.1O3-α質子導電率測量氣氛為飽和水氣下的氮氣(wet-N2)，測量溫度為350-700 oC，目的在相似的條件下找出不同參雜金屬對質子導電率的影響與趨勢。計算方面，使用密度泛函理論(DFT)系統，模擬BaZr0.9M0.1O3-α可能的機制，利用討論氧空穴形成能、質子缺陷、參雜與缺陷的相關能、質子水合能與活化能障等觀點來解釋由實驗獲得的趨勢。 結合實驗與計算可以得到質子導電率趨勢與參雜金屬半徑有密切關係，其獲得最佳導電率的參雜為In3+、Er3+、Y3+、Ho3+、Dy3+，而相對較小的參雜(Al3+、Ga3+)由於電荷的定域化降低水合能力使導電率下降，另一方面，過大的參雜金屬(Gd3+, Sm3+, Nd3+, La3+)低的導電率，是由於A-site參雜造成氧空穴減少並獲得較低的質子濃度。

The ionic conductivity of trivalent doped BaZr0.9M0.1O3-α, (M3+ = Al 、Ga 、In、Er、Y、Ho、Dy、Gd、Sm、Nd、La) have been experimentally and computationally examined in this work.Experimentally, the powder with same dopant ratios, 10%, has been initially synthesized by sol-gel method, and its physical and chemical properties have been ex-situ characterized by XRD, SEM and EDS. The synthesized powder is further pressurized and sintered at 1150℃ for 5 hours. Protonic conductivity of the resulted BaZr1-xMxO3 pellets has been investigated by both DC and AC (impedance) measurements in the wet N2 atomsphere at 350 – 700 oC. Computationally, formation energies of oxygen vacancy V_o^(..) and proton defect OH_o^., dopant-defect interaction energies , hydration energies and activation barrier of the doped BaZr0.9M0.1O3-α have been systematically examine by the means of density functional theory (DFT) calculation. The experimental measurement and computational result show that the best proton conductivity corresponds to the dopants of In3+, Er3+ ,Y3+, Ho3+, Dy3+. The conductivity decreases as the dopant radius are relatively smaller (Al3+, Ga3+) since the charge will be more localized in these dopants and reduce the hydration capability. On the other hand, the lower conductivity of the dopants with larger radius (Gd3+, Sm3+, Nd3+, La3+) can be attributed to the A-site doping problem that will reduce oxygen vacancy and eventually lower the concentration of proton defects.