Octahedral and polar phase transitions in freestanding films of SrTiO3
arxiv(2024)
摘要
From extreme strain to bending, the possibilities in the manipulation of
freestanding films of oxide perovskites bring a novel landscape to their
properties and brings them one step closer to their application. It is
therefore of great importance to fully understand the inherent properties of
such films, in which dimensionality and surface effects can play a major role
in defining the properties of the materials ground state. This paper reports
the properties of freestanding (FS) films of the canonical oxide, SrTiO3 (STO)
with thicknesses 20, 30, 40 and 80 nm. We show that the relaxed ultrathin STO
FS films become polar at temperatures as high as 85 K, in contrast to the
quantum paraelectric behavior of bulk. Our findings are based on the softening
of the ferroelectric mode towards the ferroelectric transition temperature Tc
and its consecutive hardening below Tc with further decreasing temperature,
probed with THz time domain spectroscopy in transmission mode. We find almost
no thickness dependence in Tc. Moreover, we characterize the
antiferrodistortive (AFD) phase transition in STO FS by X-ray diffraction (XRD)
probing superlattice reflections characteristic for the rotation of the TiO6
octahedra. Our results point to a higher phase transition temperature in
comparison to bulk STO, as well as an unbalanced domain population favoring the
rotation axis to be in plane. X-ray linear dichroism results further show a
preferential Ti xz/yz orbital occupancy at the surface, but with a complete
degeneracy in the t2g states in the inner part of the film indicating that the
AFD distortion does not strongly affect the t2g splitting. These findings
demonstrate that STO FS films have clearly different properties than bulk.
更多查看译文
AI 理解论文
溯源树
样例
生成溯源树,研究论文发展脉络
Chat Paper
正在生成论文摘要