Layered-structural monoclinic–orthorhombic perovskite La2Ti2O7 to orthorhombic LaTiO3 phase transition and their microstructure characterization

The layered-structural ceramics, such as lanthanum titanate (La2Ti2O7), have been known for their good temperature and low dielectric loss at microwave frequencies that make them good candidate materials for high frequency applications. However, few studies have been conducted on the synthesis optimization by sol gel reaction, in particular by acrylamide polymerization route. The interest in La2Ti2O7 ceramic has been greatly increased recently due to the effect of oriented grains. This anisotropy of the microstructure leads to anisotropy in dielectric, electrical and mechanical properties. In this study, grain oriented lanthanum titanate was produced by the sol–gel acrylamide polymerization route. The characterizations of the samples were achieved by thermal analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM). X-ray diffraction indicates that the formation of monoclinic perovskite La2Ti2O7 nanocrystals is a necessary first step to obtain orthorhombic LaTiO3 nanocomposites (with space group Pbnm). In this work we identified that the monoclinic perovskite La2Ti2O7 with space group P21 transforms its structure into one with the orthorhombic space group Cmc21 at approximately 1073 K. The microstructure associated consisted of flaky monoclinic La2Ti2O7 nanocomposites in comparison with round-shaped LaTiO3 nanocomposites.