Electrical properties and thermal expansion of strontium aluminates

Abstract

Strontium aluminate ceramics, including Sr3Al2O6, SrAl2O4 and Sr4Al14O25, synthesized by glycine-nitrate combustion and sintered at 1773 K in air, were characterized by thermal analysis, dilatometry and electrical measurements in controlled atmospheres. All studied strontium aluminates are semiconductors with electrical conductivities as low as 10(-6)-4 x 10(-5) S/cm at 1273 K in dry air. Electrical measurements in controlled atmospheres in combination with ion transference number determination demonstrated that SrAl2O4 is a mixed conductor with predominant ionic conductivity and increasing n-type and p-type electronic contributions under highly reducing and oxidizing conditions, respectively. While the behavior of electrical conductivity of Sr3Al2O6 in dry atmospheres was qualitatively similar to that of SrAl2O4, a significant increase of conductivity in wet atmospheres was attributed to a protonic contribution to electrical conduction, in correlation with thermogravimetric data and the tendency of this material to form a hydrogamet at low temperatures. The average thermal expansion coefficients of strontium aluminates, (8.5-11.1)x10(-6) K-1 at 333-1373 K, increase with increasing strontium content in the sequence Sr4Al14O25 < SrAl2O4 < Sr3Al2O6 and are essentially independent of oxygen partial pressure. (C) 2014 Elsevier B.V. All rights reserved.