Phase relations and conductivity of Sr- and La-zirconates

Abstract The formation of the strontium zirconates SrZrO 3 , Sr 4 Zr 3 O 10 , Sr 3 Zr 2 O 7 and Sr 2 ZrO 4 , and of the lanthanum zirconates La 2 Zr 2 O 7 and La 2− x Y x Zr 2 O 7 at 1450°C was investigated by x -ray powder diffraction and DTA. Three different routes of synthesis were tested. In the Sr-zirconate system, single phase orthorhombic SrZrO 3 and somewhat impure, tetragonal Sr 2 ZrO 4 were observed, whereas the formation of ordered Ruddlesden-Popper phases, Sr n Zr n −1 O 3n−2 , where n=4 and 3, could not be verifi ed. The conductivity of La 2 Zr 2 O 7 was 3.7×10 −6 S/cm at 750°C and 3.8×10 −5 S/cm at 1000°C. The conductivity of the Sr-zircon ates increases with increasing Sr/Zr ratio. Samples with a nominal composition corresponding to Sr 2 ZrO 4 have a conductivity of 7.5×10 −5 and 5.9×10 −4 S/cm at 750 and 1000°C, respectively. For all samples one observes low activation energies for ionic conduction (0.5–0.65 eV). Formation of pyrochlore structure La 2− x Y x Zr 2 O 7 from YSZ and La 2 O 3 at 1450 °C was demonstrated.