Study on Monoclinic Domain of Morphotropic High Piezoelectric Pb(Mg1/3Nb2/3)O3–PbTiO3 Single Crystals by Transmission Electron Microscopy

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0.68Pb(Mg1/3Nb2/3)O3–0.32PbTiO3 single crystals produced by the modified Bridgman technique were poled along the [001] orientation. We discuss the low-symmetry phase domain in the morphotropic phase boundary (MPB) from a fine structural viewpoint based on the investigation by transmission electron microscopy (TEM). By using the convergent beam electron diffraction (CBED) method, we observed the crystal symmetry in each of the three orientations — [001], [101], and [111] — and determined the point and space groups. We identified the point group as $m$ since the mirror symmetry in the [100] and [$10\bar{1}$] orientations was observed in CBED patterns obtained at the [001] and [101] incidences and no symmetry was observed in those obtained at the [111] incidence. The classification based on the kinematical extinction rule could not be applied because of the difference in the fundamental lattice between lattice systems $P$ and $C$. Therefore, we compared the symmetry observed in the CBED pattern with the theoretical prediction and identified the lattice system as $P$. In addition, we examined the presence or absence of the glide plane and screw axis and identified the space group as $Pm$. We showed that the spontaneous polarization ($P_{\text{s}}$) of the monoclinic (space group $Pm$) domain is in the (010) plane and lies on the Mc line connecting point T that expresses a tetragonal system directed toward the [001] orientation and point O that expresses an orthorhombic system directed toward the [101] orientation. We also revealed that four $P_{\text{s}}$ vectors exist equivalently with respect to the poling direction. The angle formed by any two of these vectors was almost orthogonal when observed from the [110] orientation.
Published by the Japan Society of Applied Physics through the Institute of Pure and Applied Physicsの論文
2006-08-15

Study on Monoclinic Domain of Morphotropic High Piezoelectric Pb(Mg1/3Nb2/3)O3–PbTiO3 Single Crystals by Transmission Electron Microscopy

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