The Effect of Transition Metal Oxide Addition on the Conductivity of Commercially Available Gd-Doped Ceria

Abstract

The effect of addition of transition metal oxides on the charge transport of commercially available Gd-doped ceria (Ce 0.9 Gd 0.1 O 2− δ ) was assessed with special emphasis on the electronic partial conductivity. The samples were doped by adding 2, 4 or 6 cat% of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">CoO</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>4</mml:mn> <mml:mo>/</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msub> <mml:mspace width=".25em"/> <mml:mspace width=".25em"/> </mml:math> or <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">FeO</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>3</mml:mn> <mml:mo>/</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:mo>,</mml:mo> </mml:math> or 2 mol% of the transition metal oxides V 2 O 5 , MnO 2 , and CuO, respectively. All samples with transition metal oxides showed predominant ionic conductivity at high temperatures and for all materials except for MnO 2 addition, the electrical conductivity was slightly increased at temperatures ≤500 °C compared to pure CGO. For Co other than for Fe addition, the electronic conductivity strongly depends on the Co concentration. Also an increasing electronic conductivity with decreasing oxygen partial pressure from 10 −8 to 10 −4 bar at temperatures below 600 °C indicates the changing redox state of Co from divalent at low oxygen partial pressures to trivalent under ambient oxygen partial pressure. Additionally, it was found that 2 mol% of CuO already lead to a significantly decreased blocking effect of the grain boundaries in the temperature range below 500 °C.

Topics & Concepts