(Ca_0.37Sr_0.63)TiO₃perovskite—an example of an unusual class of tilted perovskites

Abstract

The structure of Ca0.37Sr0.63TiO3 perovskite has been carefully investigated using electron and neutron diffraction. Electron diffraction supports the supercell and Pbcm space group previously proposed, while high resolution neutron powder diffraction data provide the basis for a new structure refinement. The distortions of the resultant structure relative to the ideal parent perovskite structure type have been decomposed into normal modes. It is found that the primary modes of distortion are octahedral tilting modes associated with the R point (k = [1/2, 1/2, 1/2]*) and the ξ = 1/4 point on the T line of symmetry (k = [1/2, 1/2, ξ]*). There is a smaller secondary, probably induced, mode of distortion involving antiferroelectric displacements of the Ti cations associated with the ξ = 1/4 point on the Δ line of symmetry (k = [0,0,ξ]*). This compound provides one of the very few currently known examples of a tilted perovskite structure that shows tilting modes associated with the ubiquitous modulation wavevectors for a value of ξ different from 0 and 1/2.

Complex antipolar2×4×22structure withPnmasymmetry inProsandeev1, Khalyavin2, Raevski3 et al. 2014Phys. Rev. B201120View full textAdd to dashboardCite

“…This antipolar structure has a rather interesting rotational octahedra (tilting) pattern of "+ + −−" type, where "+" stays for the clockwise and "−" for counterclockwise rotation of the oxygen octahedra, about the [010] p axis. A similar rotational pattern was observed in BiScO 3 thin films on SrTiO 3 [6], in (CaSr)TiO 3 [7], and in AgNbO 3 [8].…”

Thermoelectric and structural correlations in (Sr1−x−yCaxNSomaily1, Koleśnik2, Dąbrowski3 et al. 2017Phys. Rev. B6040View full textAdd to dashboardCite

“…While several groups [13][14][15][16][17] report an orthorhombic Pbnm (Pnma) symmetry for only the 0.60 < x ≤ 1.00 Carich members, others [14,15,23,55] extend this orthorhombic distortion range to also include the 0.40 ≤ x ≤ 0.60 members of the series. With even lower Ca concentrations, reports in the literature [13,16,18,55] suggest the structure of the 0.06 ≤ x < 0.40 compositions to have become tetragonal I4/mcm; however, other studies propose the orthorhombic Ibmm symmetry for the compositional range 0.10 ≤ x < 0.35 [15,19,22,23] and the formation of a superstructure with the Pbcm symmetry [14,15,19,20,22] for 0.30 ≤ x <0.40. For compositions with x ≤ 0.06, most papers confirm the structure of these slightly doped materials as cubic m m3 P [14,16].…”

“…Thus, our results confirm that I4/mcm is the appropriate symmetry for our Sr-rich compositions at room temperature. orthorhombic Pbcm [14,20]. In this space group, the positive Ti ions move off-center in their original octahedral sites to result in displacive distortions thus making this phase ferroelectric.…”

“…Perhaps this limitation is due in part to the compounded complexity of the diverse structural distortions that have so far been identified for intermediate SCT compositions [13][14][15][16][17][18][19][20][21][22][23][24][25][26]. However, such an extensive range of possible distortion induced symmetries and properties makes our goal to synthesize and investigate Nd 3+ -substituted Sr 1-x-y Ca x Nd y TiO 3 materials even more attractive and compelling.…”

High-temperature phases of multiferroic BiFe0.7Mn0.3O3

“…In-depth investigation of other possible space groups based upon analysis of superlattice reflections of the perovskite aristotype structure 19,20 failed to find any model with a significantly better fit. This analysis relates distortions around different high symmetry points in the Brillouin zone to fractional-index reflections of the P m3m cubic aristotype structure.…”