Elsevier

Solid State Ionics

Volume 179, Issues 21–26, 15 September 2008, Pages 887-890
Solid State Ionics

Influence of sintering additives of transition metals on the properties of gadolinium-doped barium cerate

https://doi.org/10.1016/j.ssi.2008.02.065Get rights and content

Abstract

In the present work the effect of MOx (where M = Cu, Ni, Zn, Fe, Co, Ti) addition on the densification behavior and electrical conductivity of BaCe0.9Gd0.1O3  δ ceramics is investigated. It was found that the small addition of these sintering additives (1 mol% in the B position) reduces both calcination and sintering temperature by ~ 250 °С and ~ 150 °С, respectively, promoting simultaneously the densification process. The relative density of the doped samples is ~ 95% in the case of Cu, Ni and Co, ~ 91% in the case of Zn, Ti and Fe, while in the case of BaCe0.9Gd0.1O3  δ it corresponds to ~ 86%. The electrical conductivity of the BaCe0.89Gd0.1M0.01O3  δ samples sintered at 1450 °С is comparable to the one of BaCe0.9Gd0.1O3  δ, sintered at 1600 °С, both in oxidizing and reducing atmospheres. Among them, the Cu- and Zn-containing samples attain significantly higher values of conductivity.

Introduction

Gadolinium doped barium cerates (Gd-doped BaCeO3 — BCG) are solid electrolytic materials of special interest for their application in electrochemical devices, due to the fact that they exhibit high protonic conductivity in hydrogen and/or water containing atmospheres at the temperature range of 600–900 °С [1]. However, there is a series of problems related to the preparation method of these materials [2], [3], [4], [5], [6], [7], including the high synthesis temperature and the insufficient density of the sintered samples. Towards the solution of the latter, the introduction of sintering additives is considered as one of the most effective and simple methods. In the present work, the influence of various transition metals' (Cu, Ni, Zn, Fe, Ti, Co) addition on the sintering behavior and electrical properties of BCG is investigated.

Section snippets

Experimental

Both the BaCe0.9Gd0.1O3  δ and the BaCe0.89Gd0.1M0.01O3  δ, (M = Cu, Ni, Zn, Fe, Co, Ti) solid solutions were prepared according to the conventional solid state reaction method. The starting materials were BaCO3, CeO2, Gd2O3 and oxides of Cu, Ni, Zn, Fe, Ti, Co. The mixed powders were initially calcined at 1400 °С in the case of BaCe0.9Gd0.1O3  δ and at 1150 °С in the case of Cu, Ni, Zn, Fe, Ti and Co-containing samples, for 2 h. Thereafter, the powders were ground and pressed into pellets, which

Results and discussion

The results of the XRD analyses indicated that all samples are characterized by single phase, orthorhombic perovskite-type structure (Fig. 1). The XRD patterns show only the peaks of BaCeO3 with orthorhombic perovskite-type structure, without the impurities phase. The corresponding lattice parameters, unit cell volume and relative densities are presented in Table 1, where it is obvious that the introduction of the sintering additives results in the increase of the samples' relative density.

Conclusions

In the present work the effect of MOx (where M = Cu, Ni, Zn, Fe, Co, Ti) addition on the sintering and electrical behavior of gadolinium-doped barium cerate was investigated. It was found that the BCG doping by small amounts of transition metals allows the decrease of both calcination and sintering temperature by 250 °С and 150 °С, respectively. Moreover, the introduction of 1% Zn, Fe, or Ti increases the samples' density by 6–7%, while in the case of Co, Ni and Cu by 10–13%. Finally, the

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