Optical detection of symmetry breaking on a nanoscale in SrTiO₃:Ca

Abstract

Spontaneous and field-induced linear birefringence is measured at low temperatures on singledomained single crystals of weakly doped SrTi0,:Ca (x=0.002 and 0.007) in order to investigate polar ordering processes near to T,-4 and 18 K, respectively. In agreement with direct polarization measurements the size of mesoscopic polar nanodomains is determined within the framework of a nonlinear polarization optical response model. Quasi-first-order Raman scattering of soft and hard polar modes, TO,, TO, and TO,, is observed on local precursor nanodomains above T,. Below T, the change of the global symmetry from D,, to C,, is reflected by selection rules imposed on first-order Raman lines in various scattering geometries.

A ferroelectric quantum phase transition inside the superconducting dome of Sr1−xCaxTiO3−δ

“…In addition, while the TO 2 mode stays hard at 171 cm −1 , the low-energy soft TO 1 mode displays a distinctive hardening in the ferroelectric state. As seen in the figure, all these features are present, not only in the insulating sample as reported previously 14 , but also in a dilute metallic sample. This implies that the low-temperature optical phonon spectrum of the metallic samples does not differ from their insulating ferroelectric counterparts.…”

“…When a small fraction of Sr atoms (x > 0.002) is replaced with isovalent Ca, Sr 1−x Ca x TiO 3 becomes ferroelectric 3 , with a Curie temperature steadily increasing with Ca content in the dilute limit 0.002 < x < 0.02 (refs 3,13,14). Macroscopic polarization below the Curie temperature has been observed in dielectric and linear birefringence measurements, and found to build up in the plane perpendicular to the tetragonal axis along the [110] and [110] directions 3,14 . Figure 1b presents the temperature dependence of the real part of the dielectric permittivity ε in our Sr 1−x Ca x TiO 3 single crystals at three different Ca contents (x = 0.0022; 0.0045; 0.009), obtained by measuring their complex conductivity.…”

Average and local structure of the Pb-free ferroelectric perovskites(Sr,Sn)TiO3and(Ba,Ca,Sn)Laurita1, Page2, Suzuki3 et al. 2015Phys. Rev. B273220View full textAdd to dashboardCite

“…7 For example, compositional substitution creates structural disorder and subsequent local dipolar interactions, such as Ca-induced polar nanoregions in Ca 2+ -substituted SrTiO 3 , which prompts a relaxor behavior in the material. 31,32 However, there was no reported evidence of an average structural transition in the Ca 2+ -substituted material. The long-range, average structure of SSTO was determined through Rietveld refinement of diffraction data collected on the NOMAD (400 K, 300 K, 200 K, and 100 K) and POWGEN (300 K and 100 K) instruments at SNS.…”

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

“…However, recent Raman scattering study [22] shows that the ferroelectric soft mode reveals only incomplete softening of the E u mode component of the F 1u -type polar optic mode at the Curie point. 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 dielectric properties analyzed by the mean field approximation were found to qualitatively agree with the model through out the whole range of composition. Following the treatment of phase transitions in the SCT system [23,26], Zhang et al [14] adopted an appropriate order-disorder model to STO18. The transverse Ising model [27] has been recently used to explain the phase transitional properties of quantum paraelectrics and quantum ferroelectrics.…”