Research School of Chemistry, Australian National University, Canberra ACT 0200, Australia.
J Phys Chem B. 2010 Dec 16;114(49):16465-70. doi: 10.1021/jp106206y. Epub 2010 Nov 18.
The mechanism of the prototype ferroelectric phase transition in BaTiO(3) is a matter of intense debate and to a large extent still wrapped in mystery. Precursor phenomena in the form of polarized clusters in paraelectric BaTiO(3) are by now believed to represent a key step into the ferroelectric phenomenon. The determination of a slower dynamics of cluster polarization flipping along with a faster order-disorder Ti hopping mode among <111> off-center sites suggests coexistence, instead of mutual exclusion, of displacive and order-disorder types, initially proposed as distinct models. However, no clear picture of the transition state has been proposed so far, which is able to provide insight into the coexistence of the paraelectric and ferroelectric phenomena. Here, by means of a dedicated molecular dynamics approach, we provide a detailed atomistic picture of intermediate regions along the transition. Therein, different time and length scales coexist as they characterize different portions of the same material. From an imbalance of dynamically and more statically polarized clusters in this highly inhomogeneous intermediate, a symmetry breaking step naturally results. Further, we find that ferroelectric nanodomains may host antiferroelectric defects, which appear as an intrinsic feature of the growing BaTiO(3) ferroelectric material.
钛酸钡中原型铁电相转变的机制是一个激烈争论的问题，在很大程度上仍然笼罩在神秘之中。现在人们相信，顺电相钛酸钡中以极化团为形式的前驱现象代表了进入铁电现象的关键步骤。极化团的翻转动力学较慢，而<111>非中心位置的钛无序跃迁模式较快，这表明取代型和无序型铁电相的共存，而不是最初提出的相互排斥。然而，到目前为止，还没有提出明确的转变态图像，该图像能够深入了解顺电相和铁电相的共存。在这里，我们通过专门的分子动力学方法，提供了沿转变过程的中间区域的详细原子图像。其中，不同的时间和长度尺度共存，因为它们代表同一材料的不同部分。在这个高度不均匀的中间区域中，由于动态和更静态极化团的不平衡，自然会导致对称破缺。此外，我们发现铁电纳米畴可能会存在反铁电缺陷，这是生长的钛酸钡铁电材料的固有特征。
