Structural phase transitions and stress accommodation in (La0.67Ca0.33MnO3)1−x:(MgO)x composite films

Abstract

Composite $({\mathrm{La}}_{0.67}{\mathrm{Ca}}_{0.33}{\mathrm{MnO}}_3{)}_{1-x}:(\mathrm{MgO}{)}_x$ films were prepared by metalorganic aerosol deposition on a (100)MgO substrate for different concentrations of the (MgO) phase $(0\mathrm{}<~x<~0.8).$ At $x\approx 0.3$ a percolation threshold in conductivity is reached, at which an infinite insulating MgO cluster forms around the ${\mathrm{La}}_{0.67}{\mathrm{Ca}}_{0.33}{\mathrm{MnO}}_3$ grains. This yields a drastic increase of the electrical resistance for films with $x>\mathrm{}\mathrm{0.3.}\mathrm{}$ The film structure is characterized by x-ray diffraction and transmission electron microscopy. The local structure of the ${\mathrm{La}}_{0.67}{\mathrm{Ca}}_{0.33}{\mathrm{MnO}}_3$ within the film depends on the MgO concentration which grows epitaxially along the domain boundaries. A different structural phase transition from the orthorhombic Pnma structure to an unusual rhombohedral $R3\mathrm{}¯c$ structure at the percolation threshold $x\approx 0.3$ is found for ${\mathrm{La}}_{0.67}{\mathrm{Ca}}_{0.33}{\mathrm{MnO}}_3.$ A three-dimensional stress accommodation in thick films through a phase transition is suggested.