Electrical conductivity of zirconia-based solid electrolyte with submicron grain size

Abstract

The electrical conductivity of the Zr(Y)O2 electro� lyte ceramics with the highest density and the grain size from 90 to 800 nm was studied by impedance spectroscopy. The ceramics was obtained by magnetic pulse compacting of weakly aggregated nanopowders and subsequent sintering. The grain boundary con� ductivity was shown to depend on the grain size. The grain boundary resistance was found to increase with an increase in the grain size in the range of 90- 800 nm. In the grain size range of 1-18 µm, according to the data obtained previously, the grain boundary resistance in the ceramics of this composition mono� tonically decreased with an increase in the grain size. This indicates that a maximum exists in the size dependence of the grainboundary resistance. One of the factors that influence the efficiency of devices with solid oxide electrolytes are the losses due to the voltage drop in the electrolyte. In this connec� tion, the technological problem of decreasing the thickness of the electrolyte layer becomes increasingly urgent. However, in the framework of the ceramic method, the thickness of membranes cannot be decreased without the corresponding decrease in the grain size. This dictates the practical significance of the present work. Attempts to obtain nanosized oxide materials with a facecentered cubic (fcc) lattice of the fluorite type are known in the literature. For ceria� based materials, it was shown (1) that these microand nanosized ceramic samples differ in both the conduc� tivity values and the character of the temperature and oxygen pressure dependences of the conductivity. The models were developed (2, 3) to describe the depen� dences observed by regarding the grain boundaries in the ceramic as a second phase. This concept is obvious for describing heterogeneous materials, for example, a mixture of a cationconducting solid electrolyte and an insulator, as it was done in the classic works of J. Maier (see, for example, (3)), but should be eluci� dated in the general case of homogeneous ceramics. On the other hand, the presence of the Ce 3+ /Ce 4+ redox system complicates the interpretation of the phenomena observed. In this connection, it is of inter� est to study the zirconiabased ceramics. Dense nano� sized Zr(Y)O2 ceramic samples with fcc lattice have not been previously obtained. It turned out to be a very difficult technical task. To succeed, we used magnetic pulse compaction of weakly agglomerated nanopow� ders obtained by laser evaporation. This method allows one to reach pressures up to 15-17 t/cm 2 .