Structure determinations for Ca₃Ti₂O₇, Ca₄Ti₃O₁₀, Ca_3.6Sr_0.4Ti₃O₁₀ and a refinement of Sr₃Ti₂O₇

Abstract

The structures of the orthorhombic RuddlesdenPopper (A,+ tBnX3,+ 1) phases Ca3Ti207 (n=2) (CaTiO3) blocks, n TiO6 octahedra thick, with single layers of CaO having a distorted NaC1 configuration. TiO6 octahedra are tilted and distorted in a very similar fashion to those in CaTiO3 (n = ~). This fact was used to determine the space groups of the layered structures. Convergent-beam electron diffraction patterns are best matched by calculations in the above space groups which are thus confirmed. Octahedral tilt angles increase slightly in the sequence n =2, 3, oo. Strontium addition reduces the octahedral tilt angles because of preferential substitution of Sr on the Ca sites within the perovskite blocks of Ca4Ti3OIo. The algorithm used to produce starting models for structure refinements is thought to be generally applicable to Ruddlesden-Popper and possibly other layered perovskite structures. It furnishes the predictions: (a) all n-even compounds in the Can+~TinO3n+l series will have space group[

Negative Thermal Expansion in Hybrid Improper Ferroelectric Ruddlesden-Popper Perovskites by Symmetry Trapping

“…Full details and fits are given in the SI. The fits reveal that the samples are stoichiometric, and we do not observe the presence of substantial asymmetry in the diffraction profile and shift in peak positions reported previously [17][18][19], suggesting that our samples have a very low concentration of stacking faults and are highly crystalline. At 500 K, on first inspection, both samples index on the expected aristotypical symmetry for these Ruddlesden-Popper n= 2 compounds, I4/mmm ( Fig.…”

Neutron Diffraction Study of the Structural Distortions in Sr3Ru2O7

“…However, the sense of rotation was reported to exhibit a complete interbilayer disorder. In Ca Ti O , large distortions (i.e., aOb) were found that consist of a mixed mode (m1#m3) (12). In La Ni O , large distortions (i.e., aOb) were found that include distortion of the octahedra (11).…”

Domains and ferroelectric switching pathways inCa3Ti2O7from first principles

“…At room temperature Ca 3 Ti 2 O 7 crystallizes in the orthorhombic polar space group A2 1 am. 20,21 This distorted structure can be decomposed into three distinct structural distortions that transform like irreducible representations (irreps) of I4/mmm:…”