Piezoelectricity and hetero-structure fluctuations in ferroelectric materials having composition near a morphotropic phase boundary

在PZT中，x=0.50附近存在铁电四方/单斜晶界和单斜晶界/三方晶界，具有很高的压电性。在这两种边界中，前者的特征是近乎垂直的边界，称为准态相边界(MPB)。为了了解MPB附近优良压电性能的物理来源，我们主要用透射电子显微镜研究了x=0.50附近的PZT样品的结晶学特征。X射线粉末衍射的初步测试表明，x=0.50和0.48的样品呈现出四方向单斜相的转变，而在单斜晶界/三方晶界附近的x=0.46样品中，在低于室温的温度范围内，基本上发现了三方相。在初步数据的基础上，用In-S…研究了这些样品的结晶学特征用透射电子显微镜观察更多的国际电信联盟。结果表明，在四方相向单斜晶系转变的过程中，在四方相中的{110}孪晶晶界形成了具有透镜状形状的单斜晶区。其特征是成核区基本不呈现生长过程，相变是通过单斜晶区的反复成核进行的。转变后的单斜相以透镜状结构域的聚集为特征。而在x=0.48的样品中，则不存在晶胞结构。在整个样品区域内只观察到花呢状结构。这表明x=0.46的样品由具有单斜晶系对称性的纳米级区域组成。换言之，X射线衍射法显示的菱面体对称性正好是平均面积。因此，这种优异的压电性能被理解为与由纳米尺寸的单斜晶区组成的花呢类型的微结构直接相关。较少

In Pb(Zr_<1-x>Ti_x)O_3 (PZT), there exist the ferroelectric tetragonal/monoclinic and monoclinic/rhombohedral phase boundaries around x=0.50, where the very high piezoelectric response has been reported. Among these two boundaries, the former is characterized by the nearly vertical boundary called the morphotropic phase boundary (MPB). In order to understand the physical origin of the excellent piezoelectric property found near the MPB, we have investigated the crystallographic features of the PZT samples around x=0.50 mainly by transmission electron microscopy.The preliminary examination by means of X-ray powder diffraction revealed that the x=0.50 and 0.48 sample exhibited the tetragonal to monoclinic transition, while in the x=0.46 sample near the monoclinic/rhombohedral boundary the rhombohedral phase was basically found in the temperature range below room temperature. Based on the preliminary data, the details of the crystallographic features of these samples were examined by in-s … More itu observation using a transmission electron microscope. The observation indicated that in the tetragonal to monoclinic transition the monoclinic regions with a lenticular shape were nucleated at the {110} twin boundary in the tetragonal phase. The characteristic features are that the nucleated regions do not basically exhibit the growth process, and that the transition proceeds by the repeated nucleation of the monoclinic regions. The monoclinic phase after the transition is then characterized by the aggregation of the lenticular domains. In the x=0.48 sample, on the other hand, there is no crystallographic domain structure. Only the tweed-type structure was observed in the whole area of the sample. This suggests that the x=0.46 sample consists of nm-sized regions with the monoclinic symmetry. In other words the rhombohedral symmetry indicating by X-ray diffraction is just on average area. The excellent piezoelectric property is thus understood be directly associated with the tweed-type microstructure consisted of the nm-size monoclinic regions. Less