Magnetic and dielectric property control in the multivalent nanoscale perovskite Eu0.5Ba0.5TiO3

Abstract

We report nanoscale Eu_0.5Ba_0.5TiO₃, a multiferroic in the bulk and candidate in the search to quantify the electric dipole moment of the electron. Eu_0.5Ba_0.5TiO₃, in the form of nanoparticles and other nanostructures is interesting for nanocomposite integration, biomedical imaging and fundamental research, based upon the prospect of polarizability, f-orbital magnetism and tunable optical/radio luminescence. We developed a [non-hydrolytic]sol–[H₂O-activated]gel route, derived from in-house metallic Ba_(s)/Eu_(s) alkoxide precursors and Ti{(OCH(CH₃)₂}₄. Two distinct nanoscale compounds of Ba:Ti:Eu with the parent perovskite crystal structure were produced, with variable dielectric, magnetic and optical properties, based on altering the oxidizing/reducing conditions. Eu_0.5Ba_0.5TiO₃ prepared under air/O₂ atmospheres produced a spherical core–shell nanostructure (30–35 nm), with perovskite Eu_0.5Ba_0.5TiO₃ nanocrystal core-insulating oxide shell layer (∼3 nm), presumed a pre-pyrochlore layer abundant with Eu³⁺. Fluorescence spectroscopy shows a high intensity ⁵D₀ → ⁷F₂ transition at 622 nm and strong red fluorescence. The core/shell structure demonstrated excellent capacitive properties: assembly into dielectric thin films gave low conductivity (2133 GΩ mm⁻¹) and an extremely stable, low loss permittivity of ε_eff ∼25 over a wide frequency range (tan δ < 0.01, 100 kHz–2 MHz). Eu_0.5Ba_0.5TiO₃ prepared under H₂/argon produced more irregular shaped nanocrystals (20–25) nm, with a thin film permittivity around 4 times greater (ε_eff 101, tan δ < 0.05, 10 kHz–2 MHz, σ ∼59.54 kΩ mm⁻¹). Field-cooled magnetization values of 0.025 emu g⁻¹ for EBTO-Air and 0.84 emu g⁻¹ for EBTO-Argon were observed. X-ray photoelectron spectroscopy analysis reveals a complex interplay of Eu^II/III/Ti^III/IV configurations which contribute to the observed ferroic and fluorescence behavior.