O3-δ Thin Films Research Articles

Oxygen-vacancy-induced atomic and electronic reconstructions in magnetic Sr(Ti0.875Fe0.125)O3-δ thin films

The atomic and electronic structures have been investigated for the multiferroic behavior in the perovskite oxides, which also can be tuned by oxygen vacancy for enhancing properties. Here epitaxial Sr(Ti0.875Fe0.125)O3-δ thin films were deposited on (001) SrTiO3 substrates by pulsed laser deposition and were post-annealed in an oxygen atmosphere. We found that the oxygen vacancies formed in high vacuum are the source of the macroscopic crystal distortion as the growth strain along out-of-plane. Moreover, it was determined that the full-filled Fe 3d states induced by oxygen vacancy effect are responsible for the decreased magnetization. This work demonstrates that the oxygen vacancy can both lead to atomic and electronic reconstructions in the perovskite films for manipulating ferroic properties.

Designing tunable band-gap and magnetization at room-temperature in Pb(Ti1-xMx)O3-δ (M=Ni and Pd) thin films

The Pb(Ti1-xMx)O3-δ (M=Ni and Pd) ferroelectric thin films prepared by a sol-gel technique have been studied by means of structural characterizations, optical and magnetic measurements. X-ray diffraction and Raman scattering results reflect the visible changes in average structure. Moreover, d8M2+ doping has important effects on the energy band structure and magnetic orderings. Optical transmittance spectra analysis indicates that Pb(Ti0.85Ni0.15)O3-δ and Pb(Ti0.85Pd0.15)O3-δ thin films present small band-gaps of 2.67eV and 2.55eV, respectively. Also, the as-grown Pb(Ti0.85M0.15)O3-δ thin films show room-temperature ferromagnetism, in contrast to PbTiO3 which is diamagnetic. A bound magnetic polaron model can be employed to explain the observed ferromagnetic behavior.

(Ba0.5Sr0.5)(Co0.8Fe0.2)O3-δ Thin Films Derived by Metal-Organic Deposition: Preparation of Nanoscaled Surface Modifications and Electrochemical Characterization

In this study, nanoscaled (Ba0.5Sr0.5)(Co0.8Fe0.2)O3-δ (BSCF) thin films (with thicknesses below 100 nm) have been successfully deposited onto NdGaO3 single crystal substrates using a metal-organic deposition (MOD) method. In contrast to physical vapor deposition techniques, e.g. pulsed-laser deposition or magnetron sputtering, BSCF thin films formed by an MOD method provide the possibility to custom-tailor the surface morphology by subsequent annealing treatments, enabling selective surface nanostructuring. Changes of surface area or phase composition (cubic, hexagonal BSCF, others) are expected to affect the catalytic activity of oxygen-transport membranes. A study of surface morphologies achieved by a variation of the post-deposition thermal treatment is presented. The electrical properties of selected MOD thin films were determined up to 800°C and compared to data for epitaxial BSCF thin films and bulk samples. Lastly, oxygen exchange kinetics were investigated by electrical conductivity relaxation measurements analyzed, in the frequency domain, yielding oxygen surface exchange coefficients kδ(T) between 400…600°C.

Effects of single-coated layer thickness on the microstructure, leakage current and dielectric tunability of Na0.5Bi0.5(Ti,Zn)O3-δ thin films prepared by metal organic decomposition

Na0.5Bi0.5(Ti,Zn)O3-δ (NBTZn) thin films with various single-coated layer thicknesses (35, 25, 20 and 15 nm) annealed at 550 °C were fabricated on indium tin oxide/glass substrates using a metal organic decomposition process. The effects of single-coated layer thickness on the crystal structure, morphology, leakage current as well as dielectric tunability are investigated. All the films exhibit polycrystalline perovskite structures with different relative intensities of (110) peaks. The highly preferred orientation in the film of 20 nm per layer (nm/l) is consistent with the typical columnar structure observed from cross-sectional morphology. Also, for the film with 20 nm/l, it exhibits the higher tunability of 43.2% and figure of merit of 8.1 at 240 kV/cm and 100 kHz due to well-crystallization and lower content of defects. Meanwhile, the effects of electric field on the tunability for all the NBTZn films and frequency on the dielectric constant-electric field loops for the film of 20 nm/l are discussed.

Ferroelectric and photovoltaic properties of transition metal doped Pb(Zr0.14Ti0.56Ni0.30)O3-δ thin films

We report nearly single phase Pb(Zr0.14Ti0.56Ni0.30)O3-δ (PZTNi30) ferroelectric having large remanent polarization (15–30 μC/cm2), 0.3–0.4 V open circuit voltage (VOC), reduced band gap (direct 3.4 eV, and indirect 2.9 eV), large ON and OFF photo current ratio, and the fast decay time. Reasonably good photo current density (1–5 μA/cm2) was obtained without gate bias voltage which significantly increased with large bias field. Ferroelectric polarization dictates the polarity of VOC and direction of short circuit current (ISC), a step forward towards the realization of noncentrosymmetric ferroelectric material sensitive to visible light.

Preparation and properties of rare earth (Eu, Tb, Ho) and transition metal (Co) co-doped BiFeO3 thin films

Ferroelectric (Bi0.9 RE 0.1)(Fe0.975Co0.025)O3-δ (RE = Eu, Tb and Ho) thin films were prepared on Pt(111)/Ti/SiO2/Si(100) substrates via a chemical solution deposition method. All thin films were crystallized in a distorted rhombohedral perovskite structure confirmed by using an X-ray diffraction and a Raman scattering analyses. Compared to the pure BiFeO3 thin film, improved electrical and ferroelectric properties were observed for the co-doped thin films. Among the thin films, the lowest leakage current density of 4.28 × 10−5 A/cm2 was measured at an applied electric field of 100 kV/cm for the (Bi0.9Ho0.1)(Fe0.975Co0.025)O3-δ thin film. This value is approximately three orders lower than that of the pure BFO thin film. Furthermore, a large remnant polarization (2P r) of 60.2 μC/cm2 and a low coercive field (2E c ) of 561 kV/cm at 980 kV/cm were observed from the (Bi0.9Ho0.1)(Fe0.975Co0.025)O3-δ thin film.

Enhancement of ferroelectricity in gadolinium (Gd) and transition metal (Ni, Co, Cr) Co-doped BiFeO3 thin films via a chemical solution deposition technique

The BiFeO3 (BFO) and the gadolinium and transition metal ions co-doped (Bi0.9Gd0.1)(Fe0.975TM0.025)O3-δ (TM = Ni, Co and Cr, BGFNi, BGFCo and BGFCr) thin films were prepared on Pt(111)/Ti/SiO2/Si(100) substrates by using a chemical solution deposition method. Compared to the pure BFO, improved electrical and ferroelectric properties were observed in the co-doped (Bi0.9Gd0.1)(Fe0.975TM0.025)O3-δ thin films. Among the thin films, the BGFCr thin film exhibited large remnant polarization (2Pr), low coercive field (2Ec), and reduced leakage current density, which are 136 μC/cm2, 1360 kV/cm at 1470 kV/cm, and 5.14 × 10-6 A/cm2 at 100 kV/cm, respectively.

Enhancement of Ferroelectricity in Rare Earth and Manganese Ions Co-doped BiFeO3 Thin Films via Chemical Solution Deposition Method

The structural and electrical properties of BiFeO3 (BFO) and rare earth metal ions (Re) co-substituted (Bi0.9Re0.1)(Fe0.9Mn0.1)O3-δ (Re = Nd, Sm, Ce and Tb) thin films prepared on Pt(111)/Ti/SiO2/Si(100) substrates via a chemical solution deposition method were investigated. The significant decrease of leakage current density and improved ferroelectric properties were observed from the co-substituted thin films. The largest remnant polarization (2Pr) (61.7 μC/cm2) and the lowest coercive field (2Ec) 657 kV/cm at 931 kV/cm were measured from the (Bi0.9Ce0.1)(Fe0.9Mn0.1)O3-δ thin film. The leakage current density value of (Bi0.9Sm0.1)(Fe0.9Mn0.1)O3-δ thin film (3.29 × 10−5A/cm2) was found to be two order lower than that of the pure BFO.

Structure and Electrical Properties of Rare Earth Substituted Bi (Fe0.975Cu0.025)O3-δ Thin Films Prepared by Chemical Solution Deposition

Thin films of BiFeO3 (BFO), Bi0.9Eu0.1Fe0.975Cu0.025O3-δ (BEuFC) and Bi0.9Dy0.1 Fe0.975Cu0.025O3-δ (BDyFC) were prepared on Pt(111)/Ti/SiO2/Si(100) substrates via a chemical solution deposition method. X-ray diffraction and Raman studies show distorted rhombohedral perovskite crystal structure for all the samples. Micro structural features and morphological changes of the BFO, BEuFC and BDyFC were examined by using a FE-SEM analysis. The leakage current density was found to be greatly reduced for the BEuFC and the BDyFC thin films. The largest remnant polarization (2Pr) 68 μC/cm2 (at 1336 kV/cm) and the lowest coercive field (2Ec) 845 kV/cm (at 931 kV/cm) were observed from the BEuFC and the BDyFC thin films, respectively.