Unusual phase transitions in ferroelectric nanodisks and nanorods
Unusual phase transitions in ferroelectric nanodisks and nanorods
复制标题
DOI：
10.1038/nature03107
复制
发表时间：
2004-12-09
期刊：
影响因子：
64.8
通讯作者：
Fu, HX
中科院分区：
文献类型：
--
作者：
Naumov, II;Bellaiche, L;Fu, HX
大块铁电体在低温下发生结构相变，产生多稳态（即多个最小值）简并态，并具有自发极化。通过施加外部电场并改变外部电场的方向来改变这些状态是诸如非易失性铁电随机存取存储器（1）（NFERAM）之类的器件的操作的关键原理。与体铁电体相比，低维有限铁电结构有望将NFERAM的存储密度提高10，000倍（2）。但这种预期的好处取决于低维结构中是否仍然存在相变和多稳态。先前的研究表明，相变在一维系统中是不可能的（3-5），并且随着维度的进一步降低，相变的可能性越来越小（3-6）。在这里，我们进行从头算研究的铁电纳米级磁盘和棒的技术上重要的Pb（Zr，Ti）O-3固溶体，并证明存在以前未知的相变在零维铁电纳米粒子。显示低温结构双稳态的磁盘的最小直径被确定为3.2 nm，使最终的NFERAM密度为60 × 10（12）位/平方英寸，即比目前可用的大五个数量级（7）。我们的研究结果表明，一个创新的使用铁电纳米结构的数据存储，并在低维系统的相变理论的基本价值。
Bulk ferroelectrics undergo structural phase transformations at low temperatures, giving multi-stable ( that is, multiple-minimum) degenerate states with spontaneous polarization. Accessing these states by applying, and varying the direction of, an external electric field is a key principle for the operation of devices such as non-volatile ferroelectric random access memories(1) (NFERAMs). Compared with bulk ferroelectrics, low-dimensional finite ferroelectric structures promise to increase the storage density of NFERAMs 10,000-fold(2). But this anticipated benefit hinges on whether phase transitions and multi-stable states still exist in low-dimensional structures. Previous studies have suggested that phase transitions are impossible in one-dimensional systems(3-5), and become increasingly less likely as dimensionality further decreases(3-6). Here we perform ab initio studies of ferroelectric nanoscale disks and rods of technologically important Pb(Zr, Ti) O-3 solid solutions, and demonstrate the existence of previously unknown phase transitions in zero-dimensional ferroelectric nanoparticles. The minimum diameter of the disks that display low-temperature structural bistability is determined to be 3.2 nm, enabling an ultimate NFERAM density of 60 x 10(12) bits per square inch that is, five orders of magnitude larger than those currently available(7). Our results suggest an innovative use of ferroelectric nanostructures for data storage, and are of fundamental value for the theory of phase transition in systems of low dimensionality.