Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, USA.
1] Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, USA [2] Department of Physics, University of Science and Technology Beijing, Beijing 100083, China.
Nat Commun. 2014;5:3172. doi: 10.1038/ncomms4172.
High-performance piezoelectrics are lead-based solid solutions that exhibit a so-called morphotropic phase boundary, which separates two competing phases as a function of chemical composition; as a consequence, an intermediate low-symmetry phase with a strong piezoelectric effect arises. In search for environmentally sustainable lead-free alternatives that exhibit analogous characteristics, we use a network of competing domains to create similar conditions across thermal inter-ferroelectric transitions in simple, lead-free ferroelectrics such as BaTiO3 and KNbO3. Here we report the experimental observation of thermotropic phase boundaries in these classic ferroelectrics, through direct imaging of low-symmetry intermediate phases that exhibit large enhancements in the existing nonlinear optical and piezoelectric property coefficients. Furthermore, the symmetry lowering in these phases allows for new property coefficients that exceed all the existing coefficients in both parent phases. Discovering the thermotropic nature of thermal phase transitions in simple ferroelectrics thus presents unique opportunities for the design of 'green' high-performance materials.
高性能压电体是基于铅的固溶体，具有所谓的准同型相界，该相界作为化学组成的函数分离出两种竞争相；因此，出现了具有强压电效应的中间低对称相。为了寻找具有类似特性的环境可持续的无铅替代品，我们使用竞争域网络在简单的无铅铁电体（如 BaTiO3 和 KNbO3）中产生横跨热铁电相变的类似条件。在这里，我们通过直接成像低对称中间相来报告这些经典铁电体中热致相界的实验观察，这些中间相表现出现有非线性光学和压电性能系数的大幅增强。此外，这些相中对称度的降低允许出现新的性能系数，这些系数超过两个母体相中所有现有系数。因此，发现简单铁电体中热相变的热致性质为“绿色”高性能材料的设计提供了独特的机会。
