abstract
The Na+-conducting ceramics of layered Na0.8Ni0.4Ti0.6O2, Na0.8Fe0.8Ti0.2O2, Na0.8Ni0.6Sb0.4O2 (structural type O3) and Na0.68Ni0.34Ti0.66O2 (P2 type) with density higher than 91% were prepared via the standard solid-state synthesis route and characterized by the impedance spectroscopy, thermal analysis, scanning electron microscopy, structure refinement using X-ray powder diffraction data, measurements of Na+ concentration cell e.m.f., and dilatometry. The conductivity of antimonate Na0.8Ni0.6Sb0.4O2, synthesized first time, was found lower than that of isostructural Na0.8Ni0.4Ti0.6O2 due to larger ion jump distance between Na+ sites. At temperatures above 420 K, transport properties of sodium cation-conducting materials are essentially independent of partial water vapor pressure. In the low-temperature range, the conductivity reversibly increases with water vapor pressure varied in the range from approximately 0 (dry air) up to 0.46 atm. The sensitivity to air humidity is influenced by the ceramic microstructure, being favored by increasing boundary area. The average thermal expansion coefficients of layered materials at 300-1173 K are in the range (13.7-16.0)x 10(-6) K-1.
keywords
OXYGEN-ION CONDUCTORS; FORMER SOVIET-UNION; SOLID ELECTROLYTES; O2 STRUCTURE; OXIDES; NASICON; ELECTROCHEMISTRY; CERAMICS; SENSOR
subject category
Materials Science
authors
Smirnova, OA; Kharton, VV; Marques, FMB
our authors
Fernando Manuel Bico Marques
Full professor