Theory of ferroelectric phase transition inSrTiO3induced by isotope replacement

Abstract

A theory to describe the dielectric anomalies and the ferroelectric phase transition induced by oxygen isotope replacement in SrTiO 3 is developed.The proposed model gives consistent explanation between apparently contradictory experimental results on macroscopic dielectric measurements versus microscopic lattice dynamical measurements by neutron scattering studies. The essential feature is described by a 3-state quantum order-disorder system characterizing the degenerated excited states in addition to the ground state of TiO 6 cluster. The effect of isotope replacement is taken into account through the tunneling frequency between the excited states. The dielectric properties are analyzed by the mean field approximation (MFA), which gives qualitative agreements with experimental results throughout full range of the isotope concentration. The phase diagram in the temperature-tunneling frequency coordinate is studied by a QMC method to confirm the qualitative validity of the MFA analysis.

Phase transition and random-field induced domain wall response in quantum ferroelectrics SrTi18O3: review and perspective

“…Similarly, as in the related impurity system Sr 1-x Ca x TiO 3 (SCT) [23], the softening stops at an energy of about 3 cm 21 , and the result is completely consistent with the data obtained on light scattering [18], hyper-Raman scattering [17], and neutron inelastic scattering [24]. These results suggest that the ferroelectric phase transition is not a purely displacive one, but becomes in part order-disorder controlled in the vicinity of T c : Yamada et al [25] proposed a new model for the ferroelectric phase transition of STO18. The essential feature is described by a 3-state quantum order-disorder system characterizing the degenerated excited states in addition to the ground state of the TiO 6 cluster.…”

“…The transverse Ising model [27] has been recently used to explain the phase transitional properties of quantum paraelectrics and quantum ferroelectrics. [25,26,28]. RFs were additionally introduced in order to describe the observed domains state properties [29].…”

Perfect Softening of the Ferroelectric Mode in the Isotope-Exchanged Strontium Titanate ofSrTiO318Studied by Light Scattering

“…It shows a small difference with the result reported on STO16 [11]. According to these experimental results about the low energy modes, theoretical and experimental works suggested a nondisplacive phase transition mechanism in STO18 [11,12]. However, quite recently the soft E u mode observed in Ref.…”

“…Since then, the phase transition mechanism of the isotope-exchanged strontium titanate SrTi 18 O 3 (hereafter abbreviated as STO18 and the ordinary one as STO16) has attracted the intense interest of many researchers in order to elucidate its phase transition mechanism related to the quantum fluctuations. The lowest energy phonon mode in STO18 has been searched for and analyzed to elucidate the soft mode dynamics near T c by many authors [7][8][9][10][11]. However, any clear softening behavior has not been reported: By Raman scattering studies, the observation of the Raman inactive soft E u mode has been tried, but the assignment of certain spectral feature to the E u mode has not been convincing and unambiguous.…”

Isotope effect on the soft-mode dynamics ofSrTiO3studied by Raman scattering

“…[10][11][12][13][14] A series of light-scattering experiments on nearly fully exchanged STO18-x has observed the ferroelectric soft E u mode, which softens toward zero-frequency at T c with less damping than in the other perovskite crystals. [15][16][17] In particular, the ideal displacive-type ferroelectric phase transition has been recently reported in Ref.…”