Department of Physics, University of Cambridge, Cambridge CB3 0HE, United Kingdom.
Phys Rev Lett. 2012 Nov 2;109(18):187601. doi: 10.1103/PhysRevLett.109.187601. Epub 2012 Oct 31.
A marked change in anelastic properties, namely, elastic softening accompanied by increased damping, has been observed in a single crystal of SrTiO(3) below ~50 K by resonant ultrasound spectroscopy. This correlates with other subtle changes in structure and properties which have been explained in the past in terms of a novel quantum state and the formation of polar clusters in an incipient ferroelectric structure. Comparison of the new data, obtained at frequencies near 1 MHz, with mechanical spectroscopy data collected at a few Hz or a few kHz, reveals a distinct dispersion with frequency and is interpreted in terms of an acoustic loss mechanism which depends primarily on the mobility under stress of ferroelastic twin walls. In most ferroelastic materials, it is found that the twin walls become immobile below some low-temperature interval due to the pinning effects of defects. It is proposed instead for SrTiO(3) that associated with the local atomic displacements within the incipient ferroelectric clusters is a change in structure of the twin walls such that their mobility becomes enhanced. We propose that the structural change is not correlated with structural changes of the bulk material but relates to increasing polarity of the walls. This interpretation implies that ferroelastic domain walls in SrTiO(3) become ferroelectric at low temperatures.
通过共振超声光谱，在 SrTiO(3)单晶中观察到在~50 K 以下弹性性质的明显变化，即弹性软化伴随着阻尼增加。这与过去根据新量子态和在初始铁电结构中形成极性团簇来解释的其他结构和性质的微妙变化有关。将在接近 1 MHz 的频率下获得的新数据与在几 Hz 或几 kHz 下收集的力学光谱数据进行比较，显示出明显的频率色散，并根据主要取决于应力下铁弹性孪晶壁迁移率的声损耗机制进行解释。在大多数铁弹性材料中，发现由于缺陷的钉扎效应，孪晶壁在某个低温间隔内变得不移动。相反，对于 SrTiO(3)，我们提出与初始铁电团簇内的局部原子位移相关的是孪晶壁结构的变化，使得它们的迁移率增强。我们提出这种结构变化与体材料的结构变化无关，而是与壁的极性增加有关。这种解释意味着 SrTiO(3)中的铁弹性畴壁在低温下变为铁电体。
