Modulations in structural and ferroelectric properties due to tensile strain in BiFeO3 films on MgAl2O4 substrates induced by thermal-expansion

The effect of tensile strain on structural and ferroelectric properties of BiFeO3 epitaxial films was investigated. The films grown by pulsed laser deposition on MgAl2O4 (0 0 1) substrates revealed monoclinic structure deviated from the bulk rhombohedral structure due to a tensile strain along the in-plane direction. The strain is induced by the difference in thermal expansion coefficients between the film and the substrate. A Poisson ratio is calculated from the in-plain and out-of-plain lattice constants at different temperatures measured by reciprocal space maps of X-ray diffraction. The small Poisson ratio compared to the bulk suggests a weaker elastic response at high temperature. The ferroelectric polarization of the tensile-strained film along the (0 0 1) is also decreased from the bulk value.

► We have grown epitaxial films of ferroelectric BiFeO3 on spinel MgAl2O4 (0 0 1) substrate by pulsed laser deposition (PLD).
► The films show monoclinic structure deviated from bulk due to the tensile strain.
► The tensile strain is induced by the difference of thermal expansion coefficients between the perovskite film and the spinel substrate.
► A Poisson ratio of BiFeO3 is obtained from the variation of lattices at different temperatures.
► The ferroelectric polarization of the BiFeO3 film is reduced due to the tensile strain as well as the poor crystalline quality induced form the intrinsic incompatible interface between perovskite and spinel.