Strong polarization enhancement in asymmetric three-component ferroelectric superlattices
Strong polarization enhancement in asymmetric three-component ferroelectric superlattices
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DOI：
10.1038/nature03261
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发表时间：
2005-01-27
期刊：
影响因子：
64.8
通讯作者：
Lowndes, DH
中科院分区：
文献类型：
--
作者：
Lee, HN;Christen, HM;Lowndes, DH
由外延工程的最新进展所推动的理论预测表明，钙钛矿型金属氧化物的超晶格中出现了丰富的复杂行为。这包括应变对极化的增强（1,2）和三分量超晶格中不对称性质的可能性(3)。本文采用高压脉冲激光沉积技术，在导电的原子平面钌酸锶（SrRuO3）层上制备了由钛酸钡（BaTiO3）、钛酸锶（SrTiO3）和钛酸钙（CaTiO3）组成的超晶格。只要BaTiO3厚度不超过CaTiO3和SrTiO3层的总厚度，BaTiO3层中的应变就能得到充分保持。通过保持全应变并结合异质界面耦合，我们发现相对于同样生长的纯BaTiO3，超晶格整体极化总体增强了50%，尽管事实上超晶格中一半的层名义上是非铁电的。我们进一步表明，在准电基质中，即使只含有BaTiO3的单细胞层的超晶格仍然是铁电的。我们的数据表明，特定的界面结构和局部不对称在极化增强中起着意想不到的作用。
Theoretical predictions - motivated by recent advances in epitaxial engineering - indicate a wealth of complex behaviour arising in superlattices of perovskite-type metal oxides. These include the enhancement of polarization by strain(1,2) and the possibility of asymmetric properties in three-component superlattices(3). Here we fabricate superlattices consisting of barium titanate (BaTiO3), strontium titanate (SrTiO3) and calcium titanate (CaTiO3) with atomic-scale control by high-pressure pulsed laser deposition on conducting, atomically flat strontium ruthenate (SrRuO3) layers. The strain in BaTiO3 layers is fully maintained as long as the BaTiO3 thickness does not exceed the combined thicknesses of the CaTiO3 and SrTiO3 layers. By preserving full strain and combining heterointerfacial couplings, we find an overall 50% enhancement of the superlattice global polarization with respect to similarly grown pure BaTiO3, despite the fact that half the layers in the superlattice are nominally nonferroelectric. We further show that even superlattices containing only single-unit-cell layers of BaTiO3 in a paraelectric matrix remain ferroelectric. Our data reveal that the specific interface structure and local asymmetries play an unexpected role in the polarization enhancement.