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

Abstract

Gd-and Mg-substituted barium titanate crystals (Ba 1%x Gd x )(Ti 1%x/2 Mg x/2 )O 3 with the Gd composition range of x > 0.1 show no ferroelectric phase transition. To discuss atomic thermal fluctuations in such unusual barium titanate crystals with cubic symmetry, accurate crystal structure analyses were performed by the maximum entropy method (MEM)/Rietveld method with the split-atom model and anharmonic temperature factor model using high-energy synchrotron radiation X-ray diffraction data. The off-centered positions of Gd ions at the Ba site in the probability density function were clearly observed at a low temperature but smeared in the high-temperature region by the over-barrier motion of Gd ions.

Size effect of the guest cation on the AlO4framework in aluminate sodalite-type oxidesM8[Al12O24](SO4)2(M = Sr2+and Ca2+) in theI43mphase

“…Although the three-site characteristic of O2 in CAS was observed by both methods, it was smeared in PDF when the Gram-Charlier method was used. A similar difference between split-atom sites and maximum positions in PDF by the Gram-Charlier method was observed for perovskite-type solid solutions (Takeda et al, 2017). The PDFs of SAS and CAS are discussed in x3.3.…”

“…Although split-atom analysis is an effective approach for investigating disorder in structure phase transitions, probability density function (PDF) analysis via the Gram-Charlier method appears to be more effective for investigating the atomic fluctuation in aluminate sodalitetype oxides. For perovskites and layered materials, atomic fluctuations in crystals as a function of temperature or composition have been investigated using PDFs (Kiat et al, 2000;Takeda et al, 2017;Noda et al, 2019;Ito et al, 2019).…”

Excellent Energy-Storage Performance in BNT-SST-LMN Lead-Free Relaxor Ferroelectric Ceramics with High Electrical Homogeneity

“…The maximal dielectric constant (ε m ) steadily drops from 1126 (x = 0) to 655 (x = 0.05), and its corresponding temperature ( T m ) gradually moves toward a lower temperature direction. This is attributed to the introduction of LMN, which causes random electric fields via increasing chaos and ion charge fluctuation. − Meanwhile, the tan δ value is less than 0.01 between 25 °C and 200 °C. Low energy dissipation is beneficial for improving BDS and η.…”

Ferroelectric order driven Eu3+ photoluminescence in BaZrxTi1−xO3 perovskite

“…12) of Eu 3+ (1.226 Å) is much smaller than that of Ba 2+ (1.610 Å) and, consequently, the lanthanide ion is over-coordinated when it is positioned at the Ba site and the possibility of occupying a lower symmetry site has to be considered. Very recent investigations including careful crystal structure determination from synchrotron X-ray diffraction data and first-principle calculations on Gd- and Dy-doped BaTiO 3 52,53 as well as the study of dielectric relaxations in Gd- and Dy-doped SrTiO 3 54,55 have provided some evidence about the off-center displacement of trivalent lanthanide ions with average size at A-site of these perovskites.…”