Unexpectedly high Curie temperature in weakly strained ferroelectric film

Abstract

Polarized Raman spectra of the epitaxial Ba0.4Sr0.6TiO3 film grown on MgO substrate with thickness of 600 nm were studied in a broad temperature range of 80–600 K and the phase transition from paraelectric to tetragonal ferroelectric phase was observed at about 500 K. This critical temperature is substantially higher than that calculated from the lattice‐mismatch strain theory. In addition, the predicted from the theory low‐temperature orthorhombic and rhombohedral phases were not observed. We ascribe the strengthening of the tetragonal ferroelectric phase to the effect of the interface‐induced build‐in electric field resulted from the interface‐accumulated charges.

Crystal Structure and the Spectral Response of the Ba‐Doped SrTiO3 Incipient Ferroelectrics

“…Vibrational spectroscopy methods were used to study the dynamics of phase transitions in various Ba‐doped SrTiO 3 samples prepared in different forms, such as, single crystals and ceramics [ 15,16 ] and films and superlattices on different substrates. [ 17–21 ] It was shown that the soft mode, which is a characteristic of displacive structural phase transitions, is active only in the ferroelectric phase. The soft‐mode behavior allows to determine the Curie temperature ( T C ).…”

Properties of the low-frequency phonon spectra of ferroelectric barium titanate-based heterostructures

“…It is known that the BST0.8 film deposited on (001)MgO substrate undergoes ferroelectric phase transitions to the tetragonal phase with the polarization perpendicularly to the substrate (c domain) at 540 K [23], whereas in the BST0.8 solid solutions this transition is observed at about 340 K [2]. Unexpectedly high Curie temperature (~500 K) was revealed in BST0.4 film due to the effect of the interface-induced build-in electric fields [24]. According to our x-ray data the BST0.5 film is cubic at room temperature with lattice parameter a = 0.3962nm, which is coherent with the Raman measurements.…”

Свойства Пленок Титаната Бария-Стронция На Кремниевой Подложке, Нанесенных Методом Высокочастотного Катодного Распыления

“…Пленка оптически анизотропна с показателями преломления обыкновенного и необыкновенного лучей, меньшими, чем для объемного кристалла (показатели преломления для объемного титаната бария n o = 2.413, n e = 2.396). Это означает, что пленка деформирована в плоскости подложки и, возможно, обладает спонтанной поляризацией [7]. Установлено, что в ходе напыления пленок на поверхности кремния образуется буферный слой толщиной порядка 18 nm, по оптическим характеристикам близкий к оксиду кремния.…”