| Autor: |
Farahmand N; The CUNY Energy Institute, City University of New York, Steinman Hall, 160 Convent Avenue, The City College of New York, New York, NY 10031, USA. sobrien@ccny.cuny.edu., McGinn CK, Zhang Q, Gai Z, Kymissis I, O'Brien S |
| Abstrakt: |
We report nanoscale Eu 0.5 Ba 0.5 TiO 3 , a multiferroic in the bulk and candidate in the search to quantify the electric dipole moment of the electron. Eu 0.5 Ba 0.5 TiO 3 , 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-[H 2 O-activated]gel route, derived from in-house metallic Ba (s) /Eu (s) alkoxide precursors and Ti{(OCH(CH 3 ) 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 0.5 Ba 0.5 TiO 3 prepared under air/O 2 atmospheres produced a spherical core-shell nanostructure (30-35 nm), with perovskite Eu 0.5 Ba 0.5 TiO 3 nanocrystal core-insulating oxide shell layer (∼3 nm), presumed a pre-pyrochlore layer abundant with Eu 3+ . Fluorescence spectroscopy shows a high intensity 5 D 0 → 7 F 2 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 0.5 Ba 0.5 TiO 3 prepared under H 2 /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. |
