Aftabuzzaman M, Helal M A, Paszkowski R, Dec J, Kleemann W, Kojima S
Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan.
Department of Physics, Pabna University of Science and Technology, Pabna 6600, Bangladesh.
Sci Rep. 2017 Sep 14;7(1):11615. doi: 10.1038/s41598-017-10985-9.
Static and dynamic heterogeneity of disordered system is one of the current topics in materials science. In disordered ferroelectric materials with random fields, dynamic polar nanoregions (PNRs) appear at Burns temperature and freeze into nanodomain state below Curie temperature (T ). This state is very sensitive to external electric field and aging by which it gradually switches into macrodomain state. However, the role of PNRs in such states below T is still a puzzling issue of materials science. Electric field and aging effects of uniaxial ferroelectric Sr Ba NbO (x = 0.40, SBN40) single crystals were studied using Brillouin scattering to clarify the critical nature of PNRs in domain states below T . On field heating, a broad anomaly in longitudinal acoustic (LA) velocity at low temperature region was due to an incomplete alignment of nanodomains caused by the interaction between PNRs. A sharp anomaly near T was attributed to the complete switching of nanodomain to macrodomain state owing to the lack of interaction among PNRs. After isothermal aging below T , the noticeable increase of LA velocity was observed. It was unaffected by cyclic temperature measurements up to T , and recovered to initial state outside of a narrow temperature range above and below aging temperature.
无序系统的静态和动态非均匀性是材料科学当前的研究热点之一。在具有随机场的无序铁电材料中，动态极性纳米区域（PNRs）在伯恩斯温度下出现，并在居里温度（T）以下冻结成纳米畴状态。这种状态对外部电场和老化非常敏感，通过老化它会逐渐转变为宏畴状态。然而，PNRs在低于T的这种状态中的作用仍然是材料科学中一个令人困惑的问题。利用布里渊散射研究了单轴铁电体SrₓBa₁₋ₓNb₂O₆（x = 0.40，SBN40）单晶的电场和老化效应，以阐明低于T的畴态中PNRs的关键性质。在电场加热时，低温区域纵向声学（LA）速度的宽异常是由于PNRs之间的相互作用导致纳米畴不完全取向引起的。接近T时的尖锐异常归因于由于PNRs之间缺乏相互作用，纳米畴完全转变为宏畴状态。在低于T的等温老化后，观察到LA速度显著增加。它不受高达T的循环温度测量的影响，并在老化温度上下的窄温度范围之外恢复到初始状态。
