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 1064105 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
hydrogarnet at low temperatures. The average thermal expansion coefficients of strontium aluminates,
(8.5–11.1)106 K1 at 333–1373 K, increase with increasing strontium content in the sequence
Sr4Al14O25 < SrAl2O4 < Sr3Al2O6 and are essentially independent of oxygen partial pressure.
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