Optical probe of ferroelectric order in bulk and thin-film perovskite titanates

Abstract

We have measured the temperature dependence of the direct band gap E g in SrTiO 3 and BaTiO 3 and related materials with quantum-paraelectric and ferroelectric properties using optical spectroscopy. We show that E g exhibits an anomalous temperature dependence with pronounced changes in the vicinity of the ferroelectric transition that can be accounted for in terms of the Fröhlich electron-phonon interaction with an optical phonon mode, the so-called soft mode. In addition, we demonstrate that these characteristic changes of E g can be readily detected even in very thin films of SrTiO 3 with a strain-induced ferroelectric order. Optical spectroscopy thus can be used as a rather sensitive probe of ferroelectric order in very thin films of these titanates and probably also in subsequent multilayers and devices.

Anisotropy of infrared-active phonon modes in the monodomain state of tetragonal SrTiO3 (110)

“…4(d) we used for the phonon modes at 170, 438 and 545 cm −1 the eigenfrequency, oscillator strength and broadening as listed in Table I and the corresponding phonon asymmetries and value of ε ∞ as reported in Refs. 37,38 . For the soft mode we used a splitting of the TO mode that is somewhat smaller than the one that was reported in Ref.…”

Influence of the central mode and soft phonon on the microwave dielectric loss near the strain-induced ferroelectric phase transitions inSrn+1TiGoian1, Kamba2, Orloff3 et al. 2014Phys. Rev. B13280View full textAdd to dashboardCite

“…The temperature dependence of ε ∞ was neglected, consistent with its behavior in other related perovskite dielectrics [24]. The parameters (ω T Oj , ω LOj , γ T Oj , γ LOj , and ε ∞ ) were held fixed to fit the spectra of the thin films.…”

Strong spin-phonon coupling in infrared and Raman spectra ofSrMnO3

“…The temperature dependence of this quantity was neglected, consistent with its behavior in other related perovskite dielectrics [13]. For Raman studies, a Renishaw RM 1000 Micro-Raman spectrometer equipped with a CCD detector and a Linkam THMS 600 temperature cell was used.…”