LA2ZR2O7 FORMATION AND OXYGEN REDUCTION KINETICS OF THE LA0.85SR0.15MNYO3, O-2(G)VERTICAL-BAR-YSZ SYSTEM

Nucleation and growth of lanthanum zirconate (LZO) between (001) singl e crystals of 9.5 mol% Y2O3-stabilized ZrO2 (YSZ) and porous La0.85Sr0 .15MnyO3=delta (y = 0.95... .10) perovskites were investigated. The pe rovskites were screen-printed on the solid electrolyte and sintered in air at 1373 K for short periods. High resolution transmission electro n microscopy, electrochemical impedance spectroscopy, and atomic force microscopy were employed for interface characterization. The manganes e concentration in the perovskite affects the onset of nucleation and the growth rate of lanthanum zirconate. Excess lanthanum oxide within the perovskite reacts immediately with YSZ to form dense LZO layers. L ayer growth kinetics is controlled by bulk diffusion of cations. Stoic hiometric perovskite leads to the reductive formation of cubic LZO isl ands at the cathode/electrolyte interface after a few minutes of sinte ring, The A-site deficient perovskite is characterized by the reductiv e dissolution of Mn into YSZ in the early sintering stage and by a pro nounced surface diffusion of cations. After the critical Mn concentrat ion in the perovskite is reached, reductive nucleation of LZO originat es. Island growth is controlled by surface diffusion of cations and th e supply of lanthanum. The electrochemical properties of the cathode/Y SZ interfaces are strongly influenced by the formation of LZO at the t riple phase boundary. Charge transfer, dissociation of adsorbed molecu lar oxygen ions, and surface diffusion of atomic oxygen are discrimina ted from electrochemical impedance data. (C) 1998 Elsevier Science B.V . All rights reserved.