Pb置換SrBi_2Ta_2O_9の格子ひずみと強誘電特性

概要

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Effects of Pb substitution on the polarization properties in SrBi_2Ta_2O_9 (SBT) were investigated using dense ceramics, and the crystal structures were refined by the Rietveld analysis of powder X-ray and neutron diffractions on the basis of A2_1am orthorhombic symmetry. The substitution of Pb at the A site (Sr site) in perovskite blocks was confirmed and the single phase of Pb_xSr_1-xBi_2Ta_2O_9 (Pb-SBT) was obtained for the samples with x≦0.6. The substitution of Pb led to an increase in Curie temperature (T_c) and coercive field (E_c). In contrast, Pb-SBT showed practically the same remanent polarization (2P_r) of SBT, around 14μC/cm^2 at 250 kV/cm, in spite of having a higher Tc than SBT. The structure analysis revealed that the spontaneous polarization (P_s) of Pb-SBT (x=0.2) was 17.3μC/cm^2, which was slightly larger than that of SBT (P_8=16.7μC/cm^2). The incorporation of Pb into SBT resulted in a higher tilt angle of TaO_6 octahedra along the α-axis (polarization direction), is partly responsible for the higher E_c observed for Pb-SBT.
2002-11-01