Domains within Domains and Walls within Walls: Evidence for Polar Domains in CryogenicSrTiO3

Abstract

Resonant piezoelectric spectroscopy shows polar resonances in paraelectric SrTiO 3 at temperatures below 80 K. These resonances become strong at T < 40 K. The resonances are induced by weak electric fields and lead to standing mechanical waves in the sample. This piezoelectric response does not exist in paraelastic SrTiO 3 nor at temperatures just below the ferroelastic phase transition. The interpretation of the resonances is related to ferroelastic twin walls which become polar at low temperatures in close analogy with the known behavior of CaTiO 3 . SrTiO 3 is different from CaTiO 3 , however, because the wall polarity is thermally induced; i.e., there exists a small temperature range well below the ferroelastic transition point at 105 K where polarity appears on cooling. As the walls are atomistically thin, this transition has the hallmarks of a two-dimensional phase transition restrained to the twin boundaries rather than a classic bulk phase transition.

Interplay between antiferrodistortive, ferroelectric, and superconducting instabilities inSr1−xCaxTiO3−Lima1, Luz2, Oliveira3 et al. 2015Phys. Rev. B323430View full textAdd to dashboardCite

“…These loss features can be understood by the formation of polar nanoregions seeded by the electric dipoles of off-center calcium sites embedded in the highly polarizable STO lattice. Even if these clusters remain disordered at low Caconcentrations they may experience glass-like freezing at low temperatures [32] or they may give rise to additional loss at higher temperatures due to interaction with eventually polar structural domain walls arising below the tetragonal phase transition [6,33].…”

“…The angle of rotation saturates to 2.1 degrees at low temperature [3,4]. This antiferrodistortive transition (an intriguing case of ferroelasticity [5]), continues to attract significant attention [6].…”

Ferroelectric Transitions at Ferroelectric Domain Walls Found from First Principles

“…This mode competes with a FE instability that is suppressed by the onset of the AFD distortion [23]. Yet, there are both theoretical and experimental indications that a polar order occurs at low temperatures within STO's FS DWs [16,[24][25][26], i.e., in the region where the otherwise dominant AFD distortions vanish. In this context, it is worth noting recent first-principles studies predicting that PbTiO 3 (PTO) [27] and related compounds [28] present a FE-AFD competition that is even stronger than the one occurring in STO.…”

Ferroelastic Domain Boundary-Based Multiferroicity

“…Furthermore, electric dipole moments were observed inside ferroelastic domain walls so that switchable ferroelectricity is potentially confined to domain walls and cannot interfere with depolarization fields and additional switching of domains in the bulk. The length scale of the active device is then restricted to the size of domain walls or to even smaller features, such as Bloch walls, inside domain walls [16][17][18][19][20][21][22]. For many applications, the aim is to produce high wall concentrations.…”