Preparation and characterization of the superlattice (Sm-doped ceria/yttria-stabilized zirconia)N electrolyte film

Abstract

As is well known, a solid oxide fuel cell(SOFC) is a device that can convert chemical energy directly into electrical energy. The possibility to grow thin films of oxide materials is of great importance in the development of SOFC. Recently, it is expected that oxide heterostructures, with almost ideal interfaces, should lead to the interesting artificial materials with some novel properties. So we have prepared superlattice electrolyte thin films.On the MgO single-crystal substrates, multilayer epitaxial thin-film heterostructures of 20 mol% samarium-oxide-doped ceria (Ce0.8Sm0.2O2-, SDC) and 8 mol% yttria-stabilized zirconia (Y2O3: ZrO2YSZ) have been deposited in turn, using the pulsed laser deposition (PLD) technique. Five different superlattices (SDC/YSZ)N (N=3, 5, 10, 20, 30) films are fabricated, keeping the total thickness constant (300 nm), but with a different number of hetero-interfaces. The choice of coupling SDC and YSZ aims to have both layers in the superlattices made of oxygen-ion conductors with compatible crystallographic features. On one hand, we have to remove any potential contribution of the deposition substrate to the total conductivity, and the superlattices may be grown on 110-oriented MgO single-crystalline wafers. On the other hand, the YSZ electrolyte film requires that the temperature should be higher, and SDC as the electrolyte leakage; both should be combined with each other, so as to have complementary advantages. In this way, not only the temperature of SOFCs is reduced, but also the leakage avoided. Because YSZ and SDC both belong to cubic fluorite structure and have similar lattice parameters, the lattice constant of YSZ is 5.14 , and the lattice constant of SDC is 5.44 . Compatible crystal properties, oxygen ion conductivity, and great matching defects can lead to a semi-coherent interface between the ZrO2 and CeO2 layers. The interface effect is obvious. X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM) and AC impedance mearurements are used to characterize the surface morphology, phase structure and electrical properties of the electrolyte film. Results show that the superlattice (SDC/YSZ)N electrolyte films will form obviously interface and better superlattice structure. This kind of thin films do not show crack, with no element diffusion at the interfaces, growing uniformly, densely and smoothly. Electrochemical measurements show a sizable increase in conductivity with increasing number of SDC/YSZ interfaces. So it is an ideal low-temperature fuel cell electrolyte materials.