Electrical Properties of Atmospheric Plasma-Sprayed La 10 (SiO 4 ) 6 O 3 Electrolyte Coatings
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JTTEE5 20:888–891 DOI: 10.1007/s11666-011-9625-1 1059-9630/$19.00 Ó ASM International
Electrical Properties of Atmospheric PlasmaSprayed La10(SiO4)6O3 Electrolyte Coatings Wei Gao, Wen-Ya Li, Han-Lin Liao, and Christian Coddet (Submitted July 28, 2010; in revised form January 6, 2011) In this present work, La10(SiO4)6O3 as a promising electrolyte candidate for intermediate temperature solid oxide fuel cells (IT-SOFCs) has been synthesized and its electrical property was investigated as a function of temperature. In order to improve the density and oxide ion conductivity of La10(SiO4)6O3, the feedstock powder was prepared by sintering the oxide mixture powders at proper sintering temperatures and times. The hexagonal apatite-type ceramic coatings with a typical composition of La10(SiO4)6O3 were deposited by atmospheric plasma spraying (APS) with different hydrogen flow rates. With increasing hydrogen flow rate oxide ion conductivity successively decreases. The highest ionic conductivity of the dense composite electrolyte coatings reaches a value of 2.4 mS/cm at 900 °C in air, which is comparable to other apatite-type lanthanum silicate (ATLS) conductors.
Keywords
apatite-type lanthanum silicate coating, atmospheric plasma spraying, intermediate temperature solid oxide fuel cells, oxide ion conductivity
In this letter, apatite-type La10(SiO4)6O3 electrolyte coatings were successfully synthesized by atmospheric plasma spraying (APS) and its electrical properties were thoroughly studied from 500 up to 900 °C.
1. Introduction
2. Experimental Procedure
Research toward electrolyte materials with high ionic conductivity and low activation energy for solid oxide fuel cells (SOFCs) with reduced operating temperature continues to be of interest. One such family of materials are the M10x(SiO4)6O31.5x compounds, where M is a metal such as a rare earth or alkaline earth ion (M = La, Mg, Ca, Sr, or Ba), which crystallize in the apatite crystal structure (P63/m) (Ref 1-12). These materials share properties similar to those of the conventional oxide ion conductors such as yttria-stabilized zirconia (YSZ), and thus, are considered potential electrolyte candidates for intermediate temperature solid oxide fuel cells (IT-SOFCs) (Ref 13-21). We have previously reported on interesting performances of compounds with the typical La10(SiO4)6O3 apatite composition, with the lattice parameters: a = 0.9684(3) nm, c = 0.7184(4) nm and a microhardness Hv0.3 = 401±9 (Ref 22, 23). When compared with other electrolyte materials, in general, the conductivity of La10(SiO4)6O3 is high indicating that oxygen interstitials may be introduced into the apatite lattice for La10(SiO4)6O3 which may benefit the oxygen ion transportation.
The polycrystalline precursor materials were synthesized in stoichiometric amounts of La2O3 (99.99%) and SiO2 (99.99%) powders. The powders were first mixed by grinding with mortar and pestle, and then uni-axially cold pressed into solid pellets at 40 MPa and reacted at 1550 °C in air for 8 h with a heating rate of 5
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