Improved Oxide Ion Conductivity in La_0.8Sr_0.2Ga_0.8Mg_0.2O₃ by Doping Co

Abstract

The effects of doping Co for the Ga site on the oxide ion conductivity of La 0.8 Sr 0.2 Ga 0.8 -Mg 0.2 O 3 have been investigated in detail. It was found that doping Co is effective for enhancing the oxide ion conductivity. In particular, a significant increase in conductivity in the low-temperature range was observed. The electrical conductivity was monotonically increased; however, the transport number for the oxide ion decreased with an increasing amount of Co. Considering the transport number and ion transport number, an optimized amount for the Co doping seems to exist at 8.5 mol % for Ga site. The theoretical electromotive forces were exhibited on H 2 -O 2 gas cell utilizing the optimized composition of La 0.8 Sr 0.2 -Ga 0.8 Mg 0.115 Co 0.085 O 3 . The diffusion characteristics of the oxide ion in La 0.8 Sr 0.2 Ga 0.8 Mg 0.115 -Co 0.085 O 3 were also investigated by using the 18 O tracer method. Since the diffusion coefficient measured by the 18 O tracer method was similar to that estimated by the electrical conductivity, the conduction of La 0.8 Sr 0.2 Ga 0.8 Mg 0.115 Co 0.085 O 3 is concluded to be almost ionic. On the other hand, an oxygen permeation measurement suggests that the oxide ion conductivity increased linearly with an increasing amount of Co. Therefore, specimens with Co content higher than 10 mol % can be considered as a superior mixed oxide ion and hole conductor. The UV-vis spectra suggests that the valence number of doped Co was changed from +3 to +2 with decreasing oxygen partial pressure; the origin of hole conduction can thus be assigned to the formation of Co 3+ . Since the amount of dopant in the Ga site was compensated with Mg 2+ , the amount of oxygen deficiency was decreased by doping Co. Therefore, it is likely that the improved oxide ion conductivity observed by doping with Co is brought about by the enhanced mobility of oxide ion.

Sol–gel synthesis and characterization of Co-doped LSGM perovskites

“…4 Following the initial discovery, [1][2][3][4][5] numerous experimental studies have been carried out on LSGM materials, which also include the effect of transition-metal doping. [6][7][8][9][10][11] It is generally believed that doping with a transition metal cation is undesirable for the ionic conductor due to the appearance of n-or p-type conduction. However, it was found that the oxide ion conductivity was also improved by doping Co for Ga in LaGaO 3 -based perovskites, 7 although hole conduction was detected at high oxygen partial pressures.…”

“…However, it was found that the oxide ion conductivity was also improved by doping Co for Ga in LaGaO 3 -based perovskites, 7 although hole conduction was detected at high oxygen partial pressures. 7,11 Nevertheless, Yamada et al 12 demonstrated that the Co-doped LSGM (LSGMC) can be used as an electrolyte for SOFCs operating at 770 • C. The 1-kW stack they tested had a fuel electrode that consisted of a mixture of NiO and Ce 0.8 Sm 0.2 O 2−δ (SDC) and a Sm 0.5 Sr 0.5 CoO 3−δ (SSC) cathode.…”

Reactivity with alkali carbonates of a newly developed oxide ionic conductor, Nd9.83(SiO4)4.5(AlO4)1.5O2 with apatite-type structure

“…2), 3) In 1995, Nakayama et al reported that the apatite-type Ln-Si-O rare earth silicates exhibited a very high oxide ionic conductivity. 4), 5) The O 2-ions at the 2a sites of the channel along the c-acis in the apatite-type (P63/m) structure are the mobile species producing the high conductivity.…”

Determinación de los números de transporte iónico de materiales basados en el galato de lantano mediante técnicas de espectroscopia de impedancia y FEM

“…Fe, Mn, Sc, etc.) are predicted to substitute preferentially for Ga 3+ position (4), hence the influence of different B-site substitutions on the transport and physicochemical properties of lanthanum gallate has been studied in order to develop novel materials for electrochemical applications (5,6). However, a negligible electronic conductivity is required for many applications, e.g.…”

“…On the other hand, Ishihara et al (5) reported that the introduction of small amounts of cobalt into the gallium sites may result in an increase of the ionic conductivity in LSGM material. Nevertheless, it was also found that the electronic conductivity increased and consequently, the ionic transport number decreased with the increasing of cobalt content.…”