Preparation and characterization of In-substituted BaSnO3 compounds

International audience; In-substituted BaSnO 3 (BaSn 1Àx In x O 3Àδ , x ¼ 0:125, 0.25 and 0.50) compounds were prepared by a gel polymerization method. Their microstructure, hydration energy and electrical properties were investigated. Single phases were confirmed by X-ray dif-fraction analysis over the whole range of substitution, and were identified as cubic perovskite-like structure. The grain size and conductivities of samples measured under dry and wet atmospheres increase significantly with indium content as such, 1À2 μm for BaSn 0:875 In 0:125 O 3Àδ (x ¼ 0:125) and 20 μm for BaSn 0:50 In 0:50 O 3Àδ (x ¼ 0.50). The highest proton conductivity at 600 ○ C, ¼ 9:5 Â 10 À4 SÁcm À1 , is obtained for BaSn 0:5 In 0:5 O 2:75 (x ¼ 0:50). Barium stannates with chemical formula derived from BaSnO 3 has recently been proposed as protonic conductors with potential applications in fuel cells. 1À6 It was shown that Y-substituted BaSnO 3 materials exhibit high proton conductivity in wet atmospheres. 5,6 Nevertheless, barium stannate based compounds exhibit a strong aversion against densification, i.e. the relative density reaches only about 90% with difficulty although sintered at 1600 ○ C for 12 h. 5,6 Such a high sintering temperature possibly results in barium volatilization leading to the decrease of proton conductivity, and also makes this oxide difficult to integrate electrochemical devices. 7,8 In the literature, the In element has received much less attention than the rare earth elements as a substituant for proton-conducting perovskites. 9À21 Matsumoto et al. 22 reported that electrical performances of BaCe 0:90 In 0:10 O 3Àδ are much more lower than those of the counterparts substituted with other trivalent dopants (Y, Tm, Yb and Sc). Zhang et al. 20 pointed out that the proton concentration and electrical properties of BaCe 0:80Àx Sm 0:20 In x O 3Àδ decrease when the indium content increases. However, Giannici et al. 21 reported that a high content of vacancies can be created by the substitution of Sn 4þ for In 3þ in BaSnO 3. Shober et al. 2 also point out that BaSn 0:5 In 0:5 O 2:75 (x ¼ 0:50) go along with high proton defects, then exhibits a high level of grain conductivity, nevertheless it is relatively unstable in severe reducing atmospheres. The literature showed that in substitution in BaCeO 3 plays a beneficial role on the stability and sinterability of proton-conducting perovskites in CO 2 atmosphere. 9,20 Moreover, indium as a second substituent improve the sinterability of BaZr 0:9 Y 0:1 O 3Àδ while yttrium enhance the proton conductivity. 18 In this paper, the effect of the substitution of Sn 4þ for In 3þ in BaSnO 3 on the micro-structure, water hydration and electrical properties has been investigated. BaSn 1Àx In x O 3Àδ (denoted x ¼ 0:125, 0.25 and 0.50 as BSIn125, BSIn25 and BSIn50 in the following) powders have been synthesized by a gel polymerization route from an aqueous solution containing cation salts. 5,6,23 The resultant precursors were heat-treated at 1200 ○ C for 4 h to obtain §