Effect of MnO2 Concentration on the Conductivity of Ce0.9Gd0.1MnxO2−δ

Abstract

Samples with the composition Ce 0.9 Gd 0.1 Mn x O 2−δ with x = 0.01, 0.02, and 0.05 Mn-addition were prepared by mixed oxide route from Ce 0.9 Gd 0.1 O 2−δ and MnO 2 and sintered at 1300 • C. The electronic conductivity was measured using a modified Hebb-Wagner technique, the electrical conductivity was investigated by impedance spectroscopy, and oxygen permeation was measured for the sample with x = 0.05. An increase of the electronic partial conductivity with increasing Mn addition was observed, which can be attributed to an additional Mn 3d-related state between the top of the valence band and the bottom of the Ce 4f band. The grain boundary conductivity was found to be suppressed for low Mn contents, but enhanced for the sample with x = 0.05.

Assessment of the Effect of Transition Metal Oxide Addition on the Conductivity of Commercial Gd-Doped Ceria

“…An extended description of the microcontact measurement method can be found in previous publications. 24,[63][64][65] Measurements were executed at temperatures between 800-400…”

“…30,46 In case of Mn, simulations and measurements showed that the increased electronic partial conductivity with increasing Mn addition can be attributed to an additional Mn 3d-related state between the top of the valence band and the bottom of the Ce 4f band. 24,29 Also Khare et al observed the development of an additional feature at the binding energy position of 2.6 eV in the valence band of CeO 2 after doping with 2-6 mol% iron. 47 This feature is related to the introduction of an additional Fe-d level which can work as a "stepping stone" for electrons within the broad ceria bandgap.…”

“…): [19][20][21][22] Some oxides such as Pr 2 O 3 or MnO 2 have been found to add an additional electronic state in the ceria bandgap and therefore to significantly increase the electronic conductivity. 23,24 Pr as a redox active material also provides an additional oxygen partial pressure dependent maximum of the electronic conductivity due to the reduction from Pr 4+ to Pr 3+ and a related polaron hopping mechanism within a certain oxygen partial pressure range. 23,25,26 A comparable effect has also been confirmed for Mn doping in YSZ or ceria after sintering at certain temperatures to preserve the Mn 3+ state within the material [27][28][29] and is also conceivable for other redox-active transition metal cations.…”

“…40 For doping with Co, a significantly increased electronic transport has been found by several groups 25,31,32,42,43 and similar observations have been reported for Fe, Cu, and Mn addition. 24,29,32 The effect was mainly attributed to exclusive segregation of the transition metals into the grain boundary core, where they are thought to either form separate highly electron conducting phases [42][43][44][45] or to decrease the grain boundary surface charge by variation of the local defect concentrations leading to a lower grain boundary resistivity of the majority charge carriers. 30,46 In case of Mn, simulations and measurements showed that the increased electronic partial conductivity with increasing Mn addition can be attributed to an additional Mn 3d-related state between the top of the valence band and the bottom of the Ce 4f band.…”

Ceramic Conductors

“…Proton conductivity may be observed in acceptor-doped perovskite oxides such as Ba 0.9 La 0.1 Zr 0.25 Sn 0.25 In 0.5 O 3−a , as studied by Skubida et al [2], and terbium-substituted lanthanum orthoniobate [3]. Oxygen ions are mobile charge carriers in materials such as substituted bismuth vanadate [4] and doped cerium oxide [5,6], as studied by Ring and Fuierer, and to a minor extent and at high temperature, they are also mobile charge carriers in ceramic proton conductors. Fluorine ions, the first mobile ions studied in solid-state ionic conductors, are present in SrF 2 -YF 3 solid solutions, as reported by Breuer et al [7].…”