A Raman scattering study of the phase transitions in SrTiO₃and in the mixed system (Sr_1-xCa_x)TiO₃at ambient pressure fromT= 300 K down to 8 K

Abstract

The room-temperature Raman spectra of Sr 1−x Ca x TiO 3 (SCT) for x = 0.06 (SCT06), 0.12 (SCT12) and 0.30 (SCT30) are shown to contain first-order Raman lines corresponding to E g and B 1g modes, which appear below 105 K in pure SrTiO 3 . The E g line shows slight asymmetry, indicating the orthorhombic structure of SCT for x 0.06. The low-temperature Raman spectra of SCT06 and SCT12 contain Raman-active modes of symmetry B 2g and E g , predicted by group theory but not observed in SrTiO 3 or SCT0.7 (x = 0.007) by previous workers. The polar hard modes TO 2 (175 cm −1 ) and TO 4 (550 cm −1 ) are present even at room temperature for SCT06 and SCT12 due to Ca 2+ -centred ferroelectric microregions. The intensity of these modes starts increasing below 55 and 80 K for SCT06 and SCT12 respectively, which are nearly 2 T c , where T c is the temperature of the smeared dielectric peak. The presence of such an extended precursor region is akin to relaxor behaviour. For SCT30, two new lines at 79 and 128 cm −1 appear below the paraelectric to antiferroelectric phase transition temperature of 230 K. It is shown that Raman lines characteristic of both ferroelectric and antiferroelectric phases are present in SCT12 below 100 K, confirming the frustration model for the highly smeared dielectric response for this composition.

Structural and magnetic properties of isovalently substituted multiferroic BiFeO3: Insights from Raman spectroscopy

“…52 A single low frequency peak positioned at 80 cm −1 of antiferroelectric origin was also observed in the antiferroelectric perovskite Sr 0.70 Ca 0.30 TiO 3 . 55 Consistent with these related compounds, we assign the 60 cm −1 mode in Bi 0.8 La 0.2 FeO 3 to an antiferroelectric displacement of the A site.…”

Elastic and anelastic anomalies in (Ca,Sr)TiO3 perovskites: Analogue behaviour for silicate perovskites

“…A recently proposed phase diagram is reproduced in Figure 1, after Carpenter et al (2006a). For Ca-rich compositions, the sequence of transitions with falling temperature is Pandey, 1999, 2001a;Ranjan et al, 2000;Mishra et al, 2001;Ouillon et al, 2002;Ranson et al, 2005;Mishra et al, 2005Mishra et al, , 2006a, and there has been a further suggestion of monoclinic symmetry (Woodward et al, 2006). From an earth sciences perspective, the CST solid solution has…”

Interface Ferroelectric Transition near the Gap-Opening Temperature in a Single-Unit-Cell FeSe Film Grown on Nb-DopedSrTiO3Substrate

“…3(a), which hardens upon cooling, corresponds to an A 1g phonon mode. [8][9][10][11] This mode disappears above the well-known STO antiferrodistortive (AFD) structural transition temperature 105 K. [12] The second peak (labeled by the blue marker) lying very close to the A 1g peak has very distinct features. This mode softens upon cooling, and saturates in energy at low temperature ( Fig.…”

“…STO undergoes the cubic-tetragonal AFD transition when cooled below 105 K, which allows the appearance of the A 1g Raman mode. [8,9,11] The AFD is a nonpolar structural distortion which suppresses the competing FE instability. [21] (See illustrations in Fig.…”