Microwave-Assisted Hydrothermal Synthesis of Fine Grained La_0.77Sr_0.20Al_0.90Mn_0.10O_3-δ

Lanthanum strontium manganese oxide (LSM) is an appealing choice for use as the internal reference electrode in an yttria-stabilized zirconia sealed internal reference high temperature oxygen sensor because its mechanical stability, thermal expansion coefficient, and electronic conduction are compatible with the conditions described in previous studies. Doping of the perovskite b-site of LSM with aluminum has been proposed to limit side reactions which impede electrical conduction and complete sealing. It has been shown previously that lanthanum strontium aluminum manganese oxide (LSAM) can be joined with yttria-stabilized tetragonal zirconia polycrystal by plastic deformation. Two micron grain size LSAM was synthesized by the solid state method.

The current work examined the microwave-assisted hydrothermal synthetic method with the goal of producing fine grained La_0.77Sr_0.20Al_0.90Mn_0.10O_3-δ at low temperature with a shorter reaction time. X-ray diffraction, Fourier-transform infrared spectroscopy, and Raman spectroscopy were used to characterize the powder. It was found that microwave heating for 6 hours in basic aqueous solution with citric acid as a complexing agent followed by calcination in air produced the cubic perovskite phase of La_0.77Sr_0.20Al_0.90Mn_0.10O_3-δ with a grain size of 25 nm. Scanning electron microscopy showed that the La_0.77Sr_0.20Al_0.90Mn_0.10O_3-δ sample formed a dense joint with yttria-stabilized tetragonal zirconia polycrystal by the grain boundary sliding method.