Spectroscopic ellipsometry of SrTiO₃ crystals applied to antiferrodistortive surface phase transition

Abstract

This work is devoted to the ellipsometric study of antiferrodistortive (AFD) O4h cubic-to-tetragonal phase transition (PT) of SrTiO 3 surface. Strong influence of surface defect structure on magnitude and temperature evolutions of surface refractive index related to PT was found and investigated. It is shown that even small surface imperfections result in enhancement and strong changes of the surface refractive index when approaching the temperature of PT. This effect is caused by emergence and evolutions in the surface of the structural changes corresponding to order parameter at the temperatures sufficiently higher than transition temperature in the bulk. In the case of structurally perfect crystal surface, the features of the temperature dependence of surface refractive index appeared to be very small and visible at the temperatures a little smaller than transition temperature for bulk that agrees well with predictions of Kaganov-Omel'yanchuk theory.

Low temperature structural transformations on the (001) surface of SrTiO3 single crystals

“…The idea of a similar phase transition on a surface has a long history [27,28], but it was robustly confirmed, apparently for the first time, only in Ref. [29] using the ellipsometric measurements on the STO surface. The surface, a very powerful defect, imposes its own symmetry and strongly influences, in particular, the orientations of the oxygen octahedra in the first layers, resulting in rotations and surface reconstruction (and therefore surface properties) very different from the bulk behavior.…”

Correlation between surface rumpling and structural phase transformation in SrTiO3

“…The phase transition involves the rotation of TiO 6 octahedra and has been featured as a classic example of a soft mode phase transition [24]. There have been conflicting reports [17][18][19][20][21][27][28][29] that a surface phase transition may occur at significantly higher temperature ~ 150 K and a second bulk phase transformations below ~70 K [25,26]. The "surface" structures of SrTiO 3 reported in ref.…”

Theoretical modeling of antiferrodistortive phase transition forSrTiO3ultrathin films

“…7 and 8), but only very recently a solid experimental proof of this effect was obtained by means of ellipsometric measurements on the STO surfaces. 9 The studied temperature dependence of the refractive index has shown a jump that is characteristic for second-order phase transitions in the temperature range close to the AFD transition in the STO bulk. Owing to considerable experimental difficulties (including the presence of defects and grain boundaries), very limited reliable information on the AFD surface transitions is available so far in the literature (e.g., the symmetry of surface phonons is not known).…”