Conductivity of A- and B-site doped LaAlO3, LaGaO3, LaScO3 and LaInO3 perovskites

doi:10.1016/S0167-2738(99)00337-9

Solid State Ionics

Volume 128, Issues 1–4, February 2000, Pages 91-103

https://doi.org/10.1016/S0167-2738(99)00337-9 Get rights and content

Abstract

The conductivity of the materials LaAlO₃, LaGaO₃, LaScO3 and LaInO₃ all doped with 10% strontium on the A-site and 10% magnesium at the B-site has been measured at different temperatures and oxygen partial pressures. The doped LaGaO₃ is found to be an almost pure ionic conductor with a conductivity of 95 mS/cm at 800°C. The conductivity of doped LaGaO₃ decreases with time due to precipitation of a secondary phase. The doped LaAlO₃ and LaScO₃ are mixed conductors in oxidising atmosphere. Their ionic conductivities at 800°C are 1.3 and 0.5 mS/cm, respectively. The conductivities given are total conductivities. The large difference in the conductivities of the investigated materials seems to be caused partly by grain boundary resistance.

Introduction

In the attempt to find new electrolyte materials for solid oxide fuel cells working at low temperature, it has been reported that LaGaO₃ doped with strontium at the A-site and magnesium at the B-site exhibits a high ionic conductivity [1], [2], [3], [4], [5], [6], [7], [8], [9]. The composition gallate exhibits a conductivity of 0.12 S/cm at 800°C [1], compared to 8 mol% yttrium-stabilised ZrO₂ where the conductivity is 0.034 S/cm at 800°C [10]. There is some disagreement about the specific composition of doped LaGaO₃ that gives the highest conductivity, but it is clear that the conductivity is among the highest obtained for oxide ion conductors stable over a wide oxygen partial pressure range. In order to understand the mechanism of the ionic conductivity in this kind of perovskite, the conductivity of doped LaScO₃, LaAlO₃ and LaInO₃ was investigated and compared to the conductivity of doped LaGaO₃. Indium, scandium and aluminium were chosen, as they are the elements with valence 3+ closest to gallium in the periodic table. It has earlier been shown that lanthanum is the element among the rare earth elements giving the highest conductivity as an A-site ion in the case of doped LnAlO₃ [11].

LaAlO₃ with different kinds of dopants either on the A- or on the B-site is known to be a mixed ionic and p-type electronic conductor at high oxygen partial pressures and ionic conductor at low partial pressures [11], [12], [13], [14]. LaScO₃ with dopants either on the A- or on the B-site is known not only to be a mixed ionic and p-type conductor but also a mixed oxide ion and proton conductor [15], [16]. Nomura et al. [17] have compared the conductivity of the materials La_0.9Sr_0.1M^IIIO₃, M=Al, Ga, Sc, In and Lu. So far investigations have been published with dopants on both sites only for the gallates.

In this work the concentration of dopants chosen is 10% Sr on the A-site and 10% Mg on the B-site. This amount of dopants makes it possible to obtain single-phase material of all four compositions.

In the following, “aluminate, gallate, scandate and indate” specifically means the 10% Sr/10% Mg doped compounds.

Section snippets

Structure

Several authors have tried to predict what kind of materials would have high oxide ion conductivity. Often the structure of the materials is thought to be an important property of the materials, when oxide ion conduction is wanted. The materials investigated here are all characterised as perovskites.

The name perovskite is generally used for metal oxides with the sum formula ABO₃, where A is the larger 12 coordinated cation and B is the smaller six coordinated cation. B is surrounded by an oxide

Experimental

LaAlO₃ and LaScO₃ were prepared with different amounts of dopants in order to determine the solubility of the dopants in the materials (see Table 3). Compositions of LaGaO₃ with high amounts of dopants are known from the literature [1], [2], [3], [4], [5], [6], [7], [8], [9]; therefore, LaGaO₃ is left out of Table 3. The interest was to find a double doped composition, where it was possible to obtain single-phase material of all four compositions. From the results shown in Table 3 it was chosen

Structure and solubilities

X-ray investigations of the prepared powders showed single phase of all four powders. The gallate, the indate and the scandate are orthorhombic, while the aluminate is rhombohedral at room temperature. The cell constants found by Rietveld refinement using the program POWDER are given in Table 2. The high temperature neutron data on aluminate show that the aluminate has a phase transition below 250°C to cubic structure. Differential scanning calorimetry (DSC) cannot detect this phase transition.

Discussion

As described above the conductivity of gallate is almost independent of p_O₂ (see Fig. 4). There is a slight increase in conductivity at oxygen partial pressures higher than 0.2 atm, but no relationship with p_O₂^1/4 is seen. To make sure that it is oxide ion conductivity, the oxygen transference number should be measured. This has not been done during this work, but it has been done by Ishihara et al. [1], they found an oxygen transference number close to unity.

The curves in Fig. 4 connecting the

Conclusion

Aluminate is a mixed electronic and ionic conductor. Gallate is an almost pure ionic conductor with the highest oxide ion conductivity of the materials investigated during this work. Scandate is a mixed p-type and ionic conductor. The ionic conductivity consists of both oxide ion and protonic conductivity. Indate is also a mixed conductor, but it is not stable in reducing atmospheres.

Doped LaGaO₃ exhibits high oxide ion conductivity because La³⁺ and Ga³⁺ have the ionic radii closest to the

Future work

Ongoing work will try to separate the bulk and the grain boundary conductivity in scandate and aluminate. This has, however, proven to be a major undertaking.

Acknowledgements

Thanks to Nikolaos Bonanos, Risø National Laboratory, and Kurt Nielsen, Technical University of Denmark, for fruitful discussions, and to Kjeld Larsen, Risø National Laboratory, for technical support whenever needed. Bente Lebech, Risø National Laboratory, is also thanked for providing time and assistance for the neutron diffraction experiments.

References (34)

T. Ishihara et al.
Solid State Ionics
(1995)
J.A. Kilner et al.
J. Power Sources
(1978)
C.B. Alcock et al.
Solid State Ionics
(1992)
K. Nomura et al.
Solid State Ionics
(1997)
P.R. Slater et al.
J. Solid State Chem.
(1998)
H. Hayashi et al.
Solid State Ionics
(1999)
J.A. Kilner et al.
Solid State Ionics
(1982)
A.F. Sammells et al.
Solid State Ionics
(1992)
L.A. Chick et al.
Mater. Lett.
(1990)
D. Lybye et al.
9th International Conference on Solid State Protonic Conductors, Bled, Slovenia, Aug. 17–21, 1998
Solid State Ionics
(1999)

E. Ruiz-Trejo et al.

Solid State Ionics

(1997)

T. Ishihara et al.

J. Am. Chem. Soc.

(1994)

T. Ishihara et al.

J. Drennan et al.

J. Mat. Chem.

(1997)

K. Huang et al.

J. Am. Ceram. Soc.

(1996)

P. Huang et al.

J. Electrochem. Soc.

(1996)

A. Petric et al.

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Conductivity of A- and B-site doped LaAlO3, LaGaO3, LaScO3 and LaInO3 perovskites

Abstract

Introduction

Section snippets

Structure

Experimental

Structure and solubilities

Discussion

Conclusion

Future work

Acknowledgements

Solid State Ionics

J. Power Sources

Solid State Ionics

Solid State Ionics

J. Solid State Chem.

Solid State Ionics

Solid State Ionics

Solid State Ionics

Mater. Lett.

Solid State Ionics

Solid State Ionics

J. Am. Chem. Soc.

J. Mat. Chem.

J. Am. Ceram. Soc.

J. Electrochem. Soc.

Conductivity of A- and B-site doped LaAlO₃, LaGaO₃, LaScO₃ and LaInO₃ perovskites