Pradhan Dhiren K, Mishra Ajay K, Kumari Shalini, Basu Abhisek, Somayazulu Maddury, Gradauskaite Elzbieta, Smith Rebecca M, Gardner Jonathan, Turner P W, N'Diaye Alpha T, Holcomb M B, Katiyar Ram S, Zhou Peng, Srinivasan Gopalan, Gregg J M, Scott J F
Geophysical Laboratory, Carnegie Institution for Science, Washington, DC, 20015, USA.
Department of Physics and Institute for Functional Nanomaterials, University of Puerto Rico, San Juan, PR, 00931, USA.
Sci Rep. 2019 Feb 8;9(1):1685. doi: 10.1038/s41598-018-38411-8.
We have studied the atomic force microscopy (AFM), X-ray Bragg reflections, X-ray absorption spectra (XAS) of the Pd L-edge, Scanning electron microscopey (SEM) and Raman spectra, and direct magnetoelectric tensor of Pd-substituted lead titanate and lead zirconate-titanate. A primary aim is to determine the percentage of Pd and Pd substitutional at the Ti-sites (we find that it is almost fully substitutional). The atomic force microscopy data uniquely reveal a surprise: both threefold vertical (polarized out-of-plane) and fourfold in-plane domain vertices. This is discussed in terms of the general rules for Voronoi patterns (Dirichlet tessellations) in two and three dimensions. At high pressures Raman soft modes are observed, as in pure lead titanate, and X-ray diffraction (XRD) indicates a nearly second-order displacive phase transition. However, two or three transitions are involved: First, there are anomalies in c/a ratio and Raman spectra at low pressures (P = 1 - 2 GPa); and second, the c/a ratio reaches unity at ca. P = 10 GPa, where a monoclinic (M) but metrically cubic transition occurs from the ambient tetragonal P4 mm structure in pure PbTiO; whereas the Raman lines (forbidden in the cubic phase) remain until ca. 17 GPa, where a monoclinic-cubic transition is known in lead titanate.
我们研究了钯取代钛酸铅和锆钛酸铅的原子力显微镜（AFM）、X射线布拉格反射、钯L边的X射线吸收光谱（XAS）、扫描电子显微镜（SEM）和拉曼光谱，以及直接磁电张量。一个主要目的是确定钯的百分比以及钯在钛位点的取代情况（我们发现几乎是完全取代）。原子力显微镜数据独特地揭示了一个意外发现：既有三重垂直（面外极化）畴顶点，也有四重面内畴顶点。这将根据二维和三维中沃罗诺伊图案（狄利克雷镶嵌）的一般规则进行讨论。在高压下，如在纯钛酸铅中一样，观察到拉曼软模，并且X射线衍射（XRD）表明存在近乎二级位移相变。然而，涉及两个或三个转变：首先，在低压（P = 1 - 2 GPa）下，c/a比和拉曼光谱存在异常；其次，在约P = 10 GPa时，c/a比达到1，此时从纯PbTiO的四方P4 mm结构发生单斜（M）但度量上为立方的转变；而拉曼线（在立方相中被禁止）一直保留到约17 GPa，此时钛酸铅中已知发生单斜 - 立方转变。
