Monoclinic distortion shrinkage and enhanced properties of La ₂MO₂O9 oxide ion conductors synthesized by an isobaric-microwave assisted method

La2MO₂O9 (LMO) ceramics are synthesized by using a novel isobaric-microwave assisted method. Monoclinic distortion shrinkage was detected according to a smaller thermodynamics parameter enthalpy (H) -3.2 kJmol-1 at the monoclinic-cubic phase transition temperature in these LMO ceramics. Even there is no direct observation of superstructure ordering from high resolution transmission electron microscopy and selected electron area diffraction patterns. Both the bulk and grain boundary conductivities are greatly enhanced below the phase transition, which is four times as high as those LMO ceramics prepared by solid state reaction method.