Structural, electrical and electrochemical properties of calcium-doped lanthanum nickelate

The present work focuses on the structural, thermo-mechanical and electrical properties of La2-xCaxNiO4 + (delta) with different calcium content (x = 0-0.4) and the electrochemical performance of the electrodes on their base in contact with a Ce0.8Sm0.2O1.9 electrolyte. It was shown that the introduction of even a small amount of calcium (x = 0.1) stabilized the crystal structure in the tetragonal syngony across the whole temperature range 25-800 degrees C. Dilatometric study of the compact samples in the entire concentration range of Ca showed no phase transitions up to 800 degrees C The total electrical conductivity, measured by a dc four-probe technique, increased with an increase in calcium content. However, electrochemical activity of the La2-xCaxNiO4 + delta - based electrodes, contrarily, drastically decreased. The polarization resistance R-eta, derived from the impedance spectroscopy data, increased from 0.18 Omega.cm(2) (x = 0) to 1.240 Omega.cm(2) (x = 0.3) at 800 degrees C. The coefficients of oxygen surface exchange (k*) and oxygen tracer diffusion (D*) calculated from the oxygen isotope exchange data for La2NiO4+delta were considerably higher than those for La1.7Ca0.3NiO4+delta (4.54-10(-7) cm.s(-1) and 3.02.10(-8) cm(2).s(-1) (x = 0); 2.91-10(-8) cm.s(-1) and 5.82.10(-10) cm(2).s(-1) (x = 0.3) at 800 degrees C, respectively). It was found that for La1.7Ca0.3NiO4+delta the rate-determining stage of oxygen surface exchange is incorporation of oxygen, while for La2NiO4+delta it is oxygen dissociative adsorption. (C) 2016 Elsevier B.V. All rights reserved.