Intrinsic Effect of the Electric Field on Ti--O Bonding in Ferroelectric BaTiO3 Probed by Resonant X-ray Emission Spectroscopy

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Ti K$\beta$ resonant X-ray emission spectra of a BaTiO3 single crystal were measured under the condition of applied electric field at room temperature. The microfocused X-ray beam was incident on the $ac$ plane at 10 μm above the negative-electroded $ab$ plane. One of two Raman peaks caused by charge transfer excitation shows a distinct energy shift in response to the field, while fluorescence peaks (K$\beta_{1,3}$, K$\beta'$, K$\beta”$, and K$\beta_{2,5}$) are insensitive to the intensity of the field. The shift is comprehended as the induced Ti off-centering in an oxygen octahedron by the electric field, not as slight lattice distortion caused by the electrostrictive effect. It is concluded that a prompt response of the Ti--O bonding to the field is an intrinsic factor determining the ferroelectric nature of BaTiO3, such as displacive type or order--disorder type.
2011-09-25