Origin of Composition Variation of Ferroelectric Phase Transition Temperature in (Ba,Ca)TiO₃ by Synchrotron Radiation Powder Diffraction

Abstract

The ferroelectric cubic–tetragonal phase transition temperature T C in (Ba1-x Ca x )TiO3 (BCT) is almost unchanged and is maximum at x ∼0.06 in the T–x phase diagram, in contrast to many other lead-free BaTiO3-based solid solutions that show a decrease in T C by atomic substitution. To investigate the peculiar atomic substitution effect in BCT, the crystal structure parameters and electron density distributions of BCT were analyzed precisely in the cubic phase by synchrotron radiation powder diffraction measurements and the maximum entropy method (MEM)/Rietveld method. The contraction of the lattice induced by the substitution of smaller Ca for Ba promotes the overlap of the electron cloud between the Ti and O atoms in the low x region, whereas it causes the repulsion between the Ti and O atoms in the high x region. The maximum T C can be attributed to the maximum bonding electron density between the Ti and O atoms at x ∼0.06.

Structural Variety of Defect Perovskite Variants M3E2X9 (M = Rb, Tl, E = Bi, Sb, X = Br, I)

“…The cubic variant ( c ) 3 occurs e.g. in SrTiO 3 with space group Pm $\bar{3}$ m 14. The crystal structure features a three dimensional network of corner‐shared [TiO 6 ] octahedra, whereas the [SrO 12 ] cuboctahedra are octahedrally connected with each other by common square faces.…”

Average and local structure of the Pb-free ferroelectric perovskites(Sr,Sn)TiO3and(Ba,Ca,Sn)Laurita1, Page2, Suzuki3 et al. 2015Phys. Rev. B303220View full textAdd to dashboardCite

“…13,14 Substitution of Ca 2+ is accompanied by a linear decrease in the cubic a lattice parameter, 36 which would suggest a depression in the T c , such as is observed in the BaTiO 3 -SrTiO 3 solid solution. 37 This has been attributed globally to a size mismatch effect of the Ba 2+ and Ca…”

Structure fluctuation in Gd- and Mg-substituted BaTiO3with cubic structure

“…16) This result made a contrast with the fact that the small T C change 19) and no apparent change in Ti-O bonding nature were observed in the (Ba 1−x Ca x )TiO 3 system. 20) The careful crystal structure analysis of (Ba 1−x Gd x )(Ti 1−x=2 Mg x=2 )O 3 revealed that Gd ions occupied the six 〈100〉 off-centered positions in the cubic phase of (Ba 1−x Gd x )(Ti 1−x=2 Mg x=2 )O 3 (0 < x ≤ 0.3) and the single site shifted along the [001] direction in the tetragonal phase of (Ba 0.94 Gd 0.06 )(Ti 0.97 Mg 0.03 )O 3 .…”

“…16) This result made a contrast with the fact that the small T C change 19) and no apparent change in Ti-O bonding nature were observed in the (Ba 1−x Ca x )TiO 3 system. 20) The careful crystal structure analysis of (Ba…”