Effect of (Zn,Mn) co-doping on the structure and ferroelectric properties of BiFeO3 thin films

BiFe_1-2xZn_xMn_xO₃ (BFZMO, with x = 0–0.05) thin films were synthesized via sol–gel method. Effects of (Zn, Mn) co-doping on the structure, ferroelectric, dielectric, and optical properties of BiFeO₃ (BFO) films were investigated. BFZMO thin films exhibit rhombohedral structure. Scanning electron microscopy (SEM) images indicate that co-doping leads to a decrease in grain size and number of defects. Leakage current density (4.60 × 10^?6 A/cm²) of BFZMO film with x = 0.02 was found to be two orders of magnitude lower than that of pristine BFO film. Owing to decreased leakage current density, saturated P–E curves were obtained. Maximum double remnant polarization of 413.2 μC/cm² was observed for BFZMO thin film with x = 0.02, while that for the BFO film was found to be 199.68 μC/cm². The reason for improved ferroelectric properties is partial substitution of Fe ions with Zn and Mn ions, which resulted in a reduction in the effect of oxygen vacancy defects. In addition, co-doping was found to decrease optical bandgap of BFO film, opening several possible routes for novel applications of these (Zn, Mn) co-doped BFO thin films.     

Microstructural,optical, and electrical characteristics of Ni/C doped BST thin films

In the present work the effect of simultaneous doping of carbon and nickel on the microstructural, optical, and electrical properties of barium strontium titanate (BST) is investigated. Thin films of BST were prepared by the sol-gel method in six different compositions ((Ba_0.6Sr_0.4)(Ni_xC_yTi_1-x-y)O₃): x?=?y?=?0.00 (BST), x?=?0.04?y?=?0.00 (BST4N), x?=?0.04?y?=?0.01 (BST4N-1C), x?=?0.04?y?=?0.02 (BST4N-2C), x?=?0.04?y?=?0.03 (BST4N-3C), and x?=?y?=?0.04 (BST4N-4C). Structural features and chemical bonds of the films were studied by TGA/DSC, XRD, FT-IR, and FE-SEM. The electrical and optical properties of the films were analysed by impedance spectroscopy and UV–VIS spectroscopy. The results show that addition of Ni and C leads to Ti⁴⁺-Ni²⁺ and Ti⁴⁺-C⁴⁺ replacements, respectively. These replacements lead to a gradual increase in the band gap energy; from 3.15?eV for BST to 3.44, 3.5, 3.66, 3.73 and 3.76?eV for BST4N, BST4N-1C, BST4N-2C, BST4N-3C, and BST4N-4C, respectively. In contrast, the dielectric loss decreases significantly from 0.055 for BST to 0.031, 0.033, 0.03, 0.022 and 0.01 for BST4N, BST4N-1C, BST4N-2C, BST4N-3C, and BST4N-4C, respectively. At the same time, the quality factor Q_f (1/ tanδ) increases substantially from 15 for BST to 32, 30, 33, 44 and 87 for BST4N, BST4N-1C, BST4N-2C, BST4N-3C, and BST4N-4C, respectively. In contrast, the frequency dependence of the capacity decreases in comparison to un-doped BST. Among all films, the BST4N-4C had the highest figure of merit (FOM), least dielectric loss, and very low frequency-dependence, making it the best candidate for tuneable device applications.     

Enhanced ferroelectric properties of (Zn,Ti) equivalent co-doped BiFeO3 films prepared via the sol-gel method

High-quality BiFe_1-2xZn_xTi_xO₃ (BFZTO with x = 0, 0.01, 0.02, 0.03, 0.04, and 0.05) films were successfully prepared on fluorine-doped tin oxide (FTO)/glass substrates via the sol-gel method. The influence of (Zn, Ti) equivalent co-doping on the structure, surface morphology, and ferroelectric properties of BFZTO films was investigated systematically. X-ray diffraction (XRD) and Raman spectra analysis indicate that co-doping results in structural transformations. Scanning electron microscope (SEM) images show that BFZTO films with x = 0.02 exhibit uniform fine grains and higher density, which is instrumental for the development of ferroelectric properties. X-ray photoelectron spectroscopy (XPS) analysis reveals that BiFe_0.96Zn_0.02Ti_0.02O₃ film can inhibit the conversion of Fe³⁺ into Fe²⁺, thereby greatly reducing oxygen vacancy concentration. Therefore, under the electric field strength of 150 kV/cm, BiFe_0.96Zn_0.02Ti_0.02O₃ film was found to have the lowest leakage current density, J = 1.13 × 10^?6 A/cm², which is five orders of magnitude lower than that of pure BiFeO₃ (BFO) film. Furthermore, this film exhibits the largest remnant polarization at room temperature, P_r = 131.9 μC/cm², which is more than twice as large as that of pure BFO (P_r = 52.6 μC/cm²). Additionally, by comparing P-E hysteresis loops of different regions on the surface of BiFe_0.96Zn_0.02Ti_0.02O₃ film, it was found that the film has high uniformity and stable overall performance. Dielectric and magnetic properties were also enhanced via (Zn, Ti) co-doping.     

Chemical and interfacial design in the visible-light-absorbing ferroelectric thin films

Ferroelectric thin films with switchable polarization and anomalous photoelectric effects have received extensive attention recently. However, the improvement of photoelectric performance is accompanied by the weakening of ferroelectricity. Here, both chemical and interlayer design are used to regulate the polarization and optical properties of BiFeO₃-based ferroelectric films. We achieved an improvement in both ferroelectricity and bandgap by chemical composition. The remanent polarization has been enhanced to 73.8 μC/cm² from 0.2 μC/cm², ascribed to the structural transition. The band gap of Eu-BiFeO₃ films has been reduced to 2.23 eV from 2.42 eV due to the unique energy level from Eu 4f, indicating the enhanced visible-light-absorbing capability. We have designed a "sandwich" interfacial structure of homogeneous Eu-BiFeO₃ films. A clever combination between optimal ferroelectricity and narrow band gap with near Eu contents of BFO films would generate an interfacial layer with a homogeneous gradient component, which should favor the switching of ferroelectric domains. The results show that the remanent polarization improved by 17 % to 86.2 μC/cm² while the band gap has also improved. Intriguingly, the short-circuit current density (J_sc) and open circuit (V_oc) of the photovoltaic signal of the optimal films are 89.0 nA and 0.412 V, respectively. This provides a simple and intelligent way to design the ferroelectric-photoelectric thin films and lays the foundation for optical information storage devices.     

Chemical solution deposition of pure and Gd-doped ceria thin films: Structural,morphological and optical properties

High quality smooth, uniform and crack-free ceria and gadolinium doped ceria (GDC) thin films were prepared on Si and Si/YSZ substrates by chemical solution deposition. The thermal behavior of Gd-Ce-O precursor was investigated by TG-DSC measurements. The phase purity and structure of deposited films were evaluated using X-ray diffraction (XRD) analysis and Raman spectroscopy. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were employed for the estimation of surface morphological features. Oxidation state of Ce ions in fabricated films was analyzed by X-ray photoelectron spectroscopy (XPS). Optical properties were evaluated by diffuse reflectance UV–vis spectrometry. Thickness of the films can be controlled by applying a certain number of spin coating cycles. A linear relation between the thickness of the films and the number of deposited layers was observed. The single-layer thickness was determined to be approximately 20 nm. The influence of annealing temperature and Gd content on the film structure, morphology and optical properties was studied and discussed. The dependence of an optical band gap as a function of grain size was demonstrated.     

Effect of MnO2 addition on relaxor behavior and electrical properties of PMNST ferroelectric ceramics

A novel ferroelectric system, 0.2Pb(Mg_1/3Nb_2/3)O₃–0.8Pb(Sn_0.46Ti_0.54)O₃ with MnO₂ addition (PMNST-Mn), was prepared. The dielectric, ferroelectric and piezoelectric properties were investigated. The results demonstrated that the addition of MnO₂ suppressed the dielectric relaxor behavior of PMNST. With the increase of MnO₂ addition, the diffuse phase transition (DPT) behavior weakened gradually. The addition of MnO₂ contributed to the decrease of the dielectric loss (tanδ) and the enhancement of ferroelectric polarization. The optimum ferroelectric and piezoelectric properties were obtained when the addition of MnO₂ is 0.75 mol%, and the remnant polarization (P_r) and mechanical quality factor (Q_m) were about 25% and 60% higher than those of PMNST, respectively. It was suggested that the formation of oxygen vacancies made the important contribution to suppressing relaxor behavior and improving the electrical properties of PMNST due to the substitution of Mn for B-site. This work provided a practicable strategy to tune electrical properties of ferroelectrics.     

Dielectric,pyroelectric, and ferroelectric properties of gadolinium doped Sr0.53Ba0.47Nb2O6 ceramic

Strontium barium niobate doped with gadolinium, with the stoichiometric formula Gd_ySr_{(0.53–3y/2)}Ba_0.47Nb₂O₆ (GSBN) was synthesized using the solid-state reaction method, with varied mol% compositions of Gd (y=0.00, 0.01, 0.03, 0.05 and 0.07). Gadolinium was chosen as a dopant with the goal of enhancing the ferroelectric and pyroelectric properties of SBN. The X-ray diffraction spectra showed that all compositions exhibit a single-phase tetragonal tungsten bronze structure. The influence of Gd as dopant on the microstructure was examined by using field emission scanning electron microscopy. The dielectric characteristics of the samples showed diffuse phase transitions. The Curie temperature of the samples shifted to lower temperature with increasing Gd concentration. The relaxor characteristic of the GSBN (above and below the Curie temperature) was described using the Curie-Weiss Law, a Gaussian distribution, and a quadratic equation. SBN doped with 3 mol% of Gd exhibits the highest remnant polarization, P_r=8.8 μC/cm², while 1 mol% Gd-doped SBN shows the highest pyroelectric coefficient of 285 µC/m² K. These qualities can be useful in security, healthcare, pollution monitoring, fire sensing, and smart energy system applications.     

Influence of Eu and Sr co-substitution on multiferroic properties of BiFeO3

Pure BiFeO₃ (BFO), and Eu-Sr co-substituted BFO samples were prepared by a sol–gel method. The effects of Eu and Sr codoped on the structural, morphological, magnetic and ferroelectric properties were systematically investigated. The X-ray diffraction and Fourier transform infrared spectroscopy reveal that substitution of Eu and Sr at the Bi site results in structural change and single phase formation. The maximum remnant magnetization of 0.287 emu/g and coercive field of 10.305 kOe are observed in the Bi_0.85Eu_0.05Sr_0.10FeO₃ sample. The suppression of spin cycloid caused from the structural distortion can play an important role in the improvement of magnetic properties. The Eu and Sr co-doped samples also exhibit good ferroelectric properties, which may be attributed to suppressing the formation of oxygen vacancies by Eu substitution.     

Aliovalent Ho3+ ion doped BaZrO3 thin films; Structural,optical and photoluminescence properties

Ho doped BaZrO3 thin film phosphors with varying Ho content (1, 2, 3 and 4?at%) were prepared via pulsed laser deposition technique. To understand the effect of doping on structural, morphological, optical and emission properties of thin films, X-ray Diffractrometer (XRD), Scanning Electron Microscopy (SEM), Spectroscopic Ellipsometry (SE) and Photoluminescence (PL) Spectroscopy have been used, respectively. Polycrystalline nature with single phase cubic crystalline structure of the films has been obtained. The optical band gap energy, as estimated by SE, has been found to increase with increase in the Ho content. The PL spectra of the synthesized phosphor exhibit green and yellow-orange as prominent emission bands in response to 328?nm as excitation wavelength.     

Highly-reliable dielectric capacitors with excellent comprehensive energy-storage properties using Bi0.5Na0.5TiO3-based relaxor ferroelectric ceramics

The development of capacitors with high reliability and good comprehensive performances is of great significance for practical applications. In this work, lead-free relaxor ferroelectric (FE) ceramics of (1-x)(0.5(Bi_0.5Na_0.5)TiO₃-0.5SrTiO₃)-xBi(Mg_2/3Nb_1/3)O₃ ((1-x)(BNT-ST)-xBMN) were prepared by a conventional solid-state reaction method. The introduction of BMN was found to enhance local structure disorder, leading to the significantly reduced size of FE nanodomains, which is responsible for the slim polarization-electric field hysteresis loops. A giant energy-storage density of 6.62 J/cm³ and a high efficiency of 82 % can be achieved simultaneously under a moderate electric field of 34 kV/mm at x = 0.08. It also exhibits high discharge density ～ 2.74 J/cm³, large power density ～ 248 MW/cm³ and ultrafast discharge rate ～ 28 ns at 20 kV/mm in addition to excellent temperature (10–130 °C) and frequency (1–100 Hz) stabilities. These results demonstrate that the (1-x)(BNT-ST)-xBMN ceramic system is a promising lead-free candidate for advanced pulsed power capacitor applications.     

Structural,thermal, dielectric and ferroelectric properties of K0.5Bi0.5TiO3 ceramics

Dense K_0.5Bi_0.5TiO₃ (KBT) lead-free ceramics were prepared by conventional solid reaction route. Their temperature behavior (up to 600 °C) was investigated by X-ray diffraction, DSC, dielectric spectroscopy and electric field-polarization technique. The first temperature dependent Raman scattering studies were also performed. X-ray and Raman scattering results show that samples exhibit a single perovskite structure with cubic symmetry at temperatures higher than approximately 400 °C and with coexistence of the cubic and tetragonal phases below this temperature. Two structural phase transitions between tetragonal phases in temperature range 200–225 °C and between tetragonal and cubic ones near 400 °C are observed. The content of the tetragonal phase increases with decreasing temperature and at room temperature it reaches more than 70%. Temperature- dependent P-E loops and pyroelectric data revealed a polar behavior in KBT up to about 400 °C, which means that the intermediate phase (～270–380 °C) is rather ferroelectric than antiferroelectric.     

Dielectric and ferroelectric properties of Ho-doped BiFeO3 nanopowders across the structural phase transition

We have studied Ho-doped BiFeO₃ nanopowders (Bi_1−xHo_xFeO₃, x = 0–0.15), prepared via sol-gel method, in order to analyse the effect of substitution-driven structural transition on dielectric and ferroelectric properties of bismuth ferrite. X-ray diffraction and Raman study demonstrated that an increased Ho concentration (x ≥ 0.1) has induced gradual phase transition from rhombohedral to orthorhombic phase. The frequency dependent permittivity of Bi_1−xHo_xFeO₃ nanopowders was analysed within a model which incorporates Debye-like dielectric response and dc and ac conductivity contributions based on universal dielectric response. It was shown that influence of leakage current and grain boundary/interface effects on dielectric and ferroelectric properties was substantially reduced in biphasic Bi_1−xHo_xFeO₃ (x > 0.1) samples. The electrical performance of Bi_0.85Ho_0.15FeO₃ sample, for which orthorhombic phase prevailed, was significantly improved and Bi_0.85Ho_0.15FeO₃ has sustained strong applied electric fields (up to 100 kV/cm) without breakdown. Under strong external fields, the polarization exhibited strong frequency dependence. The low-frequency remnant polarization and coercive field of Bi_0.85Ho_0.15FeO₃ were significantly enhanced. It was proposed that defect dipolar polarization substantially contributed to the intrinsic polarization of Bi_0.85Ho_0.15FeO₃ under strong electric fields at low frequencies.     

Towards facile fabrication of photonics components from inorganic and hybrid sol-gel films. Preparation and optical properties characterization

New trends towards development of integrated optics and miniaturization of photonic devices require fabrication of miniaturized photonic components. Fabrication of waveguiding films with designed optical properties is a fundamental process for production of planar integrated devices.We report here preparation of thin layers based on TiO₂ precursor (TET – titanium(IV) ethoxide) and SiO₂ precursors, namely inorganic (TEOS – tetraethyl orthosilicate) or organically modified (GLYMO ? 3-glycidoxypropyltrimethoxysilane) as candidates for potential application in the planar integrated circuits.The thin layers were deposited on soda-lime glass substrates using the sol-gel method and dip-coating technique and processed at relatively low temperature (up to 300 °C). Several parameters e.g. a) the type of SiO₂ precursor, b) the presence of complexing agent for TET and c) heat treatment temperature were tested for their influence on thickness and refractive index of the obtained films.Furthermore, a few series of sol-gel films activated with luminescent dye (Rhodamine B) was fabricated. The influence of the above-listed parameters on luminescent properties of the films was characterized because of lack of systematic study in the literature in this aspect. Moreover, a spectrum of the light at the output of a chosen luminescent dye-doped waveguiding film excited by laser source was investigated.In addition, the subject of our investigations were films prepared at 200 °C with various amounts of TET and organically modified SiO₂ precursor in concentration range not presented before. Their optical properties such as homogeneity and values of optical band gap of TiO₂ clusters were explored. For selected samples the waveguide properties including the optical losses were evaluated. For the first time, hybrid films with presented composition and refractive index in range of 1.59–1.71 were used for patterning by nanoimprint technique allowing for reproduction of periodic structures, which may serve for example as grating couplers or DFB (distributed feedback) resonators.     

Structural,electrical, and optical properties of Ti-doped ZnO films fabricated by atomic layer deposition

High-quality Ti-doped ZnO films were grown on Si, thermally grown SiO₂, and quartz substrates by atomic layer deposition (ALD) at 200°C with various Ti doping concentrations. Titanium isopropoxide, diethyl zinc, and deionized water were sources for Ti, Zn, and O, respectively. The Ti doping was then achieved by growing ZnO and TiO₂ alternately. A hampered growth mode of ZnO on TiO₂ layer was confirmed by comparing the thicknesses measured by spectroscopic ellipsometry with the expected. It was also found that the locations of the (100) diffraction peaks shift towards lower diffraction angles as Ti concentration increased. For all samples, optical transmittance over 80% was obtained in the visible region. The sample with ALD cycle ratio of ZnO/TiO₂ being 20 had the lowest resistivity of 8.874 × 10⁻⁴ Ω cm. In addition, carrier concentration of the prepared films underwent an evident increase and then decreased with the increase of Ti doping concentration.     

Structural,optical and electrical properties of low temperature grown undoped and (Al,Ga) co-doped ZnO thin films by spray pyrolysis

Aluminum and gallium co-doped ZnO (AGZO) thin films were grown by simple, flexible and cost-effective spray pyrolysis method on glass substrates at a temperature of 230 °C. Effects of equal co-doping with aluminum (Al) and gallium (Ga) on structural, optical and electrical properties were investigated by X-ray diffraction (XRD), UV–vis–NIR spectrophotometry and Current–Voltage (I–V) measurements, respectively. XRD patterns showed a successful growth with high quality polycrystalline films on glass substrates. The predominant orientation of the films is (002) at dopant concentrations ≤2 at% and (101) at higher dopant concentrations. Incorporation of Al and Ga to the ZnO crystal structure decreased the crystallite size and increased residual stress of the thin films. All films were highly transparent in the visible region with average transmittance of 80%. Increasing doping concentrations increased the optical band gap, from 3.12 to 3.30 eV. A blue shift of the optical band gap was observed from 400 nm to 380 nm with increase in equal co-doping. Co-doping improved the electrical conductivity of ZnO thin films. It has been found from the electrical measurements that films with dopant concentration of 2 at% have lowest resistivity of 1.621×10⁻⁴ Ω cm.     

Eu3+ doped ferroelectric CaBi2Ta2O9 based glass-ceramic nanocomposites: Crystallization kinetics,optical and dielectric properties

We report Eu³⁺ doped transparent glass-ceramics (GCs) containing bismuth layer-structured ferroelectric (BLSF) CaBi₂Ta₂O₉ (CBT) as the major crystal phase. The CBT crystal phase was generated in a silica rich glass matrix of SiO₂-K₂O-CaO-Bi₂O₃-Ta₂O₅ glass system synthesized by melt quenching technique followed by controlled crystallization through ceramming heat-treatment. Non-isothermal DSC study was conducted to analyze crystallization kinetics of the glass in order to understand the crystallization mechanism. The optimum heat-treatment protocol for ceramization of precursor glass that has been determined through crystallization kinetics analysis was employed to fabricate transparent GCs containing CBT nanocrystals, which was otherwise difficult. Structural analysis of the GCs was carried out using XRD, TEM, FESEM and Raman spectroscopy and results confirmed the existence of CBT nanocrystals. The transmittance and optical band gap energies of the GCs were found to be less when compared to the precursor glass. The refractive indices of the GCs were increased monotonically with increase in heat-treatment time, signaling densification of samples upon heat-treatment. The dielectric constants (ε_r) of the GCs were progressively increased with increase in heat-treatment duration indicating evolution of ferroelectric CBT crystals phase upon heat-treatment.     

Structural,electrical, and linear/nonlinear optical characteristics of thermally evaporated molybdenum oxide thin films

Homogeneous thin films of Molybdenum oxide (MoO₃) were grown on quartz and glass substrates using the thermal evaporation method. XRD results showed that the MoO₃ powder has a polycrystalline structure with an orthorhombic crystal system whereas the MoO₃ thin films have amorphous nature. SEM images showed that the MoO₃ thin films have a nearly uniform surfaces with worm-like shape grains. The film thickness influences on the linear and nonlinear optical characteristics of MoO₃ thin films that were examined using spectrophotometric measurements and from which, the linear optical constants of the MoO₃ thin films were estimated. The electronic transition type was determined as a direct allowed one. The values of the optical band gap were obtained to be in the range of 3.88–3.72 eV. The dispersion parameters, third-order nonlinear optical susceptibility, and the nonlinear refractive index of the MoO₃ thin films were determined and interpreted in the light of the single oscillator model. The temperature dependence of the DC electrical conductivity and the corresponding conduction mechanism for the MoO₃ films were investigated at temperatures ranging from 303 to 463 K.     

Oxygen plasma-assisted ultra-low temperature sol-gel-preparation of the PZT thin films

PbTi_1-xZr_xO₃ (PZT) thin films prepared by sol-gel method have paid much attention due to the excellent performances in piezoelectric, dielectric, ferroelectric and electro-optical. However, the high crystallization temperature of the PZT thin films restricts the compatibility with modern COMS technology. In this work, PbZr_0.52Ti_0.48O₃ (PZT) ferroelectric thin films were successfully prepared by sol-gel method at an ultra-low temperature (～450 °C) in an oxygen plasma-assisted environment. A large spontaneous polarization ～30 μC/cm² and a large dielectric breakdown ～2,900 kV/cm were obtained in the sample annealed at 450 °C for 25 h. We believe that the oxygen plasma-assisted ultra-low temperature (OPAULT) annealing process is a promising way for the sol-gel technology applied in the modern COMS devices.     

Pyroelectric,ferroelectric, piezoelectric and dielectric properties of Na0.5Bi0.5TiO3 ceramic prepared by sol-gel method

Sodium bismuth titanate (BNT) nanopowder of molar composition 50/50 (Na_0.5Bi_0.5TiO₃) was prepared by a sol-gel processing method. The structure and microstructure of the precursor gel as well as the ferroelectric, pyroelectric, dielectric and piezoelectric properties of the BNT were studied. BNT crystallized in the rhombohedra perovskites structure Na_0.5Bi_0.5TiO₃ was obtained from the precursor gel by heating at 700 °C for 2 h in air. The BNT ceramic at 1100 °C sintering temperature present high crystallinity, good dielectric properties at 1 kHz (ε′=885, tan δ=0.03, T_c=370 °C), piezoelectric properties (k₃₃=0.39, c₃₃=105 GPa, e₃₃=12.6 C/m², d₃₃=120 pC/N), high remnant polarization (P_r=47 μC/cm²) and pyroelectric coefficient ($p$=707 μC/m² K) and low coercive field (E_c=55 kV/cm). Hence, the BNT prepared by sol-gel method could be used for silicon based memory device application where a low synthesis temperature is a key requirement.