Material Science Department, Università di Milano-Bicocca, I-20125 Milano, Italy.
Nanoscale. 2017 Jul 13;9(27):9572-9580. doi: 10.1039/c6nr09817g.
Using temperature-resolved dielectric spectroscopy in the range of 75-320 K we have inspected the solid-like and liquid-like arrangements of nanometric dipoles (polar nanoregions) embedded in sodium-enriched potassium-tantalate-niobate (KNTN), a chemically-substituted complex perovskite crystal hosting inherent substitutional disorder. The study of order versus direction is carried out using Fröhlich entropy measurements and indicates the presence of four long-range symmetry phases, two of which are found to display profoundly anisotropic features. Exotic phases are found for which the dipoles at one fixed temperature manifest a liquid reorientational response along one crystal axis and a solid-like behavior along another axis. The macroscopic anisotropy observed in the sequence of different phases is found to match a microscopic order-disorder sequence typical of nominally pure perovskites. Moreover, experimental demonstration of the onset of a frozen state above transitions is provided.
利用 75-320 K 温度分辨介电谱，我们研究了嵌入富含钠的钾钽铌酸盐（KNTN）中的纳米偶极子（极性纳米区）的固态和液态排列，这是一种具有固有取代无序的化学取代的复杂钙钛矿晶体。通过 Fröhlich 熵测量研究了顺序与方向之间的关系，结果表明存在四个长程对称相，其中两个相表现出明显的各向异性特征。对于某些奇特的相，在一个固定温度下，偶极子表现出沿着一个晶轴的液体重取向响应和沿着另一个轴的固态行为。在所研究的不同相中观察到的宏观各向异性与名义上纯钙钛矿的典型微观有序-无序序列相匹配。此外，还提供了在相变以上出现冻结态的实验证据。
