Preparation and electrical properties of Nd and Mn co-doped Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> thin films

Ferroelectric thin films of Nd and Mn co-doped bismuth titanate, Bi_3.15Nd_0.85Ti_3−x Mn _x O₁₂ (BNTM) (x = 0–0.1), were fabricated on Pt/TiO₂/SiO₂/Si(100) substrates by a sol–gel technique. The BNTM films had a polycrystalline perovskite structure and uniform and dense surface morphologies. A lattice distortion was observed in the BNTM films due to Mn ion doping. The ferroelectric measurement of the films indicated that the values of coercive field (E _c ) decreased gradually with the increase of the Mn content (x), however, the remanent polarization (P _r ) increase firstly and then decrease with the increase of x. The sample with x = 0.05 had optimum electrical properties and a maximum 2P _r value. The 2P _r and 2E _c values of the film at a maximum applied electric field of 400 kV/cm were 38.3 μC/cm² and 180 kV/cm, respectively. Moreover, this BNTM capacitors did not show fatigue behaviors after 1.0 × 10¹⁰ switching cycles at a frequency of 1 MHz, suggesting a fatigue-free character. The main reason for the increase of the 2P _r and the decrease of the 2E _c might be attributed to the lattice distortion in BNTM films due to Mn ion doping.     

Preparation of <Emphasis Type="Italic">p</Emphasis>-type conducting transparent CuCrO<Subscript>2</Subscript> and CuAl<Subscript>0.5</Subscript>Cr<Subscript>0.5</Subscript>O<Subscript>2</Subscript> thin films by sol–gel processing

CuCrO₂ and CuAl_0.5Cr_0.5O₂ thin films were prepared by sol–gel processing and subsequent two-step annealing in air and inert gas atmosphere. Phase pure films with delafossite structure were obtained by adjusting the respective temperatures. The related phase development strongly affects the optical and electrical performance, giving leeway for optimization. The resulting CuCrO₂ (16 Ωcm, transmittance 21%) and CuAl_0.5Cr_0.5O₂ (11 Ωcm, transmittance 49%) films showed p-type conductivity by their positive Seebeck coefficients. The microstructure of the systems was characterized by scanning and transmission electron microscopy and correlated to the growth of different crystalline phases during the annealing steps. Thereby, crystal thermodynamics also affects the respective film performance, alleviating delafossite formation from the amorphous phase.     

Microstructure,dielectric properties and optical band gap control on the photoluminescence behavior of Ba[Zr<Subscript>0.25</Subscript>Ti<Subscript>0.75</Subscript>]O<Subscript>3</Subscript> thin films

Ba[Zr_0.25Ti_0.75]O₃ (BZT) thin films were synthesized by the complex polymerization method and heat treated at 400 °C for different times and at 700 °C for 2 h. These thin films were analyzed by X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, field emission gun-scanning electron microscopy (FEG-SEM) and atomic force microscopy (AFM), Ultraviolet–visible (UV–vis) absorption spectroscopy, electrical and photoluminescence (PL) measurements. FEG-SEM and AFM micrographs showed that the microstructure and thickness of BZT thin films can be influenced by the processing times. Dielectric constant and dielectric loss of BZT thin films heat treated at 700 °C were approximately 148 and 0.08 at 1 MHz, respectively. UV–vis absorption spectra suggested the presence of intermediary energy levels (shallow and deep holes) within the band gap of BZT thin films. PL behavior was explained through the optical band gap values associated to the visible light emission components.     

Permeation studies on transparent multiple hybrid SiO<Subscript>2</Subscript>-PMMA coatings-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> barriers on PEN substrates

In this work we report the performance of permeation barriers based on organic/inorganic multilayer stacks. We have used PMMA-SiO₂ (poly methyl methacrylate-silica) hybrid films synthesized through a sol–gel route as organic–inorganic components, whereas Al₂O₃ thin films were used as the inorganic component. The hybrid layers were deposited by dip coating and the Al₂O₃ by atomic layer deposition (ALD), films were prepared on polyethylene naphthalene (PEN) substrates. The permeability of the films and stacks is evaluated using helium as the diffusion gas in a custom made ultra-high vacuum system. The results show that permeability for PEN is reduced from 5 × 10⁻³ g/m²-day to about 9 × 10⁻⁵ g/m²-day for the best multiple barrier evaluated. Increased barrier properties are due to the increasing in the path and hence the lag-time of the permeating gas. In particular, we report the surface roughness of the different layers and its impact on the barrier performance. The hybrid layers reduced notably the roughness of the bare PEN substrate improving the quality of the Al₂O₃ layer in the barrier. The optical transmittance of the barriers in the visible region is higher than 80% in all the studied cases.     

Multifunctional performances of nanocomposite SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> doped cationic EBODAC film coated on natural cellulose matrix

Reverse micellar microemulsions were utilised to synthesise stable lead titanate colloids from typical sol–gel type molecular precursors. The particles of a few nanometres in diameter that formed by hydrolysis in the micelle cores demonstrated a nanocrystalline texture without the need for thermal treatment. In a chemical solution deposition routine based on the nanoparticle dispersions, ferroelectric PbTiO₃ thin films showing excellent remanent polarisation of more than 50 μC cm⁻² were derived. The electrical characteristics of the layers were correlated to their microstructure which was controlled by the precursor composition and the annealing conditions. A columnar morphology that was realised by spinning on coatings of up to 100 nm in individual thickness proved most favourable with respect to the ferroelectric performance of the films.     

Enhanced ferroelectric properties of Ce-substituted BiFeO<Subscript>3</Subscript> thin films prepared by sol–gel process

Ce-substituted BiFeO₃ film (BCFO film) have been prepared by sol–gel process on F doped SnO₂ (FTO)/glass substrates. The effects of Ce substitution on the structural and electrical properties have been reported. X-ray diffraction data confirmed the R3c structure with the elimination of all secondary phases. We observed an increase in the remnant polarization (Pr) with Ce substitution and obtained a maximum value of ∼84 μC/cm² in 5% Ce-substituted film. The dielectric constant of the films was increased from 280 to about 420 for the BiFeO₃ film and 5% Ce-substituted BCFO film, respectively and the films showed excellent dielectric loss behavior. Moreover, the leakage current was substantially reduced by the Ce substitution.     

Optical,electrical, and electrochemical behavior of p-type nanostructured SnO<Subscript>2</Subscript>:Ni (NTO) thin films

The physical and electrochemical properties of sol-gel synthesized nickel-doped tin oxide (NTO) thin films were investigated. The X-ray diffraction results showed that NTO samples exhibited a tetragonal structure. The average crystallite size and the unit cell volume of the films were reduced by Ni increment, while the stacking fault probability was increased. Furthermore, the field-emission scanning electron microscopy images clearly displayed that the worm-like surface morphology of the SnO₂ thin films was altered to the spherical feature in 3 and 10 mol% NTO samples. Moreover, by virtue of Ni incorporation, the average transparency of the SnO₂ thin films rose up from 67 to 85% in the visible region; also, the optical band gap of the SnO₂ sample (3.97 eV) increased and the thin film with 3 mol% dopant concentration showed a maximum value of 4.22 eV. The blue/green emission intensities of photoluminescence spectra of SnO₂ thin film changed via Ni doping. The Hall effect measurements revealed that by Ni addition, the electrical conductivity of tin oxide thin films altered from n- to p-type and the carrier concentration of the films decreased due to the role of Ni²⁺ ions which act as electron acceptors in NTO films. In contrast, 20 mol% Ni-doped sample had the highest mobility about 9.65 cm² (V s)^?1. In addition, the cyclic voltammogram of NTO thin films in KOH electrolyte indicated the charge storage capacity and the surface total charge density of SnO₂ thin films enhanced via Ni doping. Moreover, the diffusion constant of the samples increased from 2?×?10^?15 to 6.5?×?10^?15 cm² s^?1 for undoped and 5 mol% dopant concentration. The electrochemical impedance spectroscopy of the NTO thin films in two different potentials showed the different electrochemical behaviors of n- and p-type thin films. It revealed that the 20 mol% NTO thin film had maximum charge transfer at lower applied potential.     

Sol–gel derived 12BaO·7Al<Subscript>2</Subscript>O<Subscript>3</Subscript> thin films using metal alkoxides

The 12BaO·7Al₂O₃ (B12A7) thin films have been prepared via sol–gel process. Optical and electrical properties of B12A7 films have been investigated. The films were coated on soda lime float glass by the dip coating process, and annealed in air and hydrogen (H₂) at 450 °C for 2 h. The UV absorption edge was red shifted for films annealed in H₂ atmosphere. The B12A7 films had high transparency about 90% in wide visible range with maximum of 95% at 575 nm wavelength. The sheet resistance of the 300 nm films corresponding to 90.57 and 0.974 kΩ per square has been observed for air and H₂ annealed, respectively.     

Dielectric properties and I-V characteristics of (Pb<Subscript>0.4</Subscript>Sr<Subscript>0.6</Subscript>)TiO<Subscript>3</Subscript> thin films improved by TiO<Subscript>2</Subscript> buffer layers

A TiO₂ thin buffer layer was introduced between the (Pb_0.4Sr_0.6)TiO₃ (PST) film and the Pt/Ti/SiO₂/Si substrate in an attempt to improve their electrical properties. Both TiO₂ and PST layers were prepared by a chemical solution deposition method. It was found that the TiO₂ buffer layer increased the (100)/(001) preferred orientation of PST and decreased the surface roughness of the films, leading to an enhancement in electrical properties including an increase in dielectric constant and in its tunability by DC voltage, as well as a decrease in dielectric loss and leakage current density. At an optimized thickness of the TiO₂ buffer layer deposited using 0.02 mol/l TiO₂ sol, the 330-nm-thick PST films had a dielectric constant, loss and tunability of 1126, 0.044 and 60.7% at 10 kHz, respectively, while the leakage current density was 1.95 × 10⁻⁶ A/cm² at 100 kV/cm.     

Influence of YSZ buffer layer on the electric properties of compositionally graded (Ba,Sr)TiO<Subscript>3</Subscript> thin film

Compositionally graded Ba_1−x Sr _x TiO₃ (BST) (0 ≤ x ≤ 0.4) thin films were fabricated on Pt/Ti/SiO₂/Si and YSZ/Pt/Ti/SiO₂/Si substrates by a modified sol–gel technique. The YSZ buffer layer was prepared by RF magnetron sputtering. The microstructure of the graded BST films was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The results showed that all the films have uniform and crack-free surface with a perovskite structure. The graded BST film with an YSZ buffer layer has larger dielectric constant and lower dielectric loss. The leakage current density of the graded BST film with an YSZ buffer layer lowers two orders than the film without buffer layer. The improved electric properties of the graded films with an YSZ buffer layer was attributed to the YSZ buffer layer act as an excellent seeding layer to enhance the graded BST film growth.     

Physical and photoelectrochemical characterization of CuCrO2 single crystal

CuCrO₂ single crystal, elaborated by the flux method, is a narrow-band-gap semiconductor crystallizing in the delafossite structure with an indirect optical transition at 2.12 eV. The relatively longer Cu–Cu is consistent with the semi-conducting behavior. The conductivity in the (001) plans is thermally activated and occurs predominantly by small polaron hopping through mixed-valence states Cu^+/2+ in conformity with a classical dielectric behavior. The activation energy (0.05 eV) gave an effective mass of 9 m _o, indicating that the levels in the vicinity of the Fermi level E _f are strongly localized. The oxide shows an excellent chemical stability over the whole pH range; the semi-logarithmic plot gave an exchange current density of 0.7 mA cm⁻² and a corrosion potential of 0.18 V_/SCE in KOH (0.5 M) electrolyte. The electrochemical study is confined in (001) plans, and reversible oxygen intercalation is evidenced from the cyclic voltammetry. The Mott–Schottky plot (C⁻²-V) is characteristic of p type conduction and exhibits a linear plot from which a flat band potential of +0.21 V_/SCE and a holes density N _A of 5.06 × 10¹⁴ cm⁻³ were obtained. The photocurrent is due to Cu⁺: d → d transition and the valence band is positioned at 5.34 eV below vacuum.     

Characteristics of Ag/Bi<Subscript>3.25</Subscript>La<Subscript>0.75</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript>/p-Si heterostructure prepared by sol-gel processing

The metal-ferroelectric-semiconductor (MFS) heterostructure has been fabricated using Bi_3.25La_0.75Ti₃O₁₂ (BLT) as a ferroelectric layer by sol-gel processing. The effect of annealing temperature on phase formation and electrical characteristics of Ag/BLT/p-Si heterostructure were investigated. The BLT thin films annealed at from 500°C to 650°C are polycrystalline, with no pyrochlore or other second phases. The C-V curves of Ag/BLT/p-Si heterostructure annealed at 600°C show a clockwise C-V ferroelectric hysteresis loops and obtain good electrical properties with low current density of below 2×10⁻⁸ A/cm² within ±4 V, a memory window of over 0.7 V for a thickness of 400 nm BLT films. The memory window enlarges and the current density reduces with the increase of annealing temperature, but a annealing temperature over 600°C is disadvantageous for good electrical properties.     

Study of the optimal condition for electroplating of Bi2S3 thin films and their photoelectrochemical characteristics

Bismuth sulfide (Bi₂S₃) thin films were electrodeposited from non-aqueous dimethyl sulfoxide medium containing Bi(NO₃)₃ and thiourea as the precursor salts, triethanol amine as the complexing agent, and TritonX-100 as the surface active agent. The prepared films were subjected to rigorous experimentation in order to validate their potential candidature for solar cells. The films exhibited band gap energy of ∼1.3 eV and resistivity of the order of 2 × 10⁶ Ω cm at room temperature as was obtained from UV–Vis spectroscopy and four-probe measurements, respectively. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and energy dispersive analysis of X-ray were employed to reveal the morphology, structure, and chemical composition of the film matrix. The Bi₂S₃ films were found to be non-decomposable up to the temperature of 1,000 °C with the help of thermogravimetry–differential thermal analysis. The Nyquist and Mott–Schottky plots derived from electrochemical impedance spectroscopy measurements provided important information regarding electrical and semiconducting properties of the films. The n-type film with a donor density of the order of ∼10²³ m⁻³ displayed reasonable photoactivity under illumination and is recommended as a promising candidate for potential photoelectrochemical applications.     

Magnesium ion-conducting gel polymer electrolytes dispersed with fumed silica for rechargeable magnesium battery application

Effect of fumed silica dispersion on poly(vinylidene fluoride-co-hexafluoropropylene)-based magnesium ion-conducting gel polymer electrolyte has been studied using various physical and electrochemical techniques. The composite gel electrolytes are free-standing and flexible films with enough mechanical strength. The optimized composition with 3 wt.% filler offers a maximum ionic conductivity of ∼1.1 × 10⁻² S cm⁻¹ at ∼25 °C with good thermal and electrochemical stabilities. The Mg²⁺ ion conduction in the gel nanocomposite film is confirmed from the cyclic voltammetry, impedance spectroscopy, and transport number measurements. The space-charge layers formed between filler particles and gel electrolyte are responsible for the enhancement in ionic conductivity. The applicability of the gel nanocomposite to a rechargeable battery is examined by fabricating a prototype cell consisting of Mg [or Mg-multiwalled carbon nanotube (MWCNT) composite] and MoO₃ as negative and positive electrodes, respectively. The discharge capacity and the rechargeability of the cell have been improved when Mg metal is substituted by Mg-MWCNT composite. The discharge capacity of the optimized cell has found to be ∼175 mAh g⁻¹ of MoO₃ for an initial ten charge–discharge cycles.     

Calorimetric investigations of luminescent films polycarbonate (PC) doped with europium complex [Eu(TTA)<Subscript>3</Subscript>(H<Subscript>2</Subscript>O)<Subscript>2</Subscript>]

Polymers doped with rare earth complexes are advantaged in film production for many applications in the luminescent field. In this luminescent polycarbonate (PC) films doped with diaquatris(thenoyltrifluoroacetonate)europium(III) complex [Eu(TTA)₃(H₂O)₂] were prepared and their calorimetric and luminescent properties in the solid state are reported. The thermal behavior was investigated by utilization of differential scanning calorimetry (DSC) and thermogravimetry (TG). Due of the addition of rare earth [Eu(TTA)₃(H₂O)₂] into PC matrix, changes were observed in the thermal behavior concerning the glass transition and thermal stability. Characteristic broadened narrow bands arising from the ⁵D₀ → ⁷F_J transitions (J = 4−0) of Eu³⁺ ion indicate the incorporation of the Eu³⁺ ions in the polymer. The luminescent films show enhancement emission intensity with an increase of rare earth concentration in polymeric matrix accompanied by decrease in thermal stability.     

Effect of crystallographic structure on electrical and mechanical characteristics of Sm<Subscript>2</Subscript>O<Subscript>3</Subscript>-Doped CeO<Subscript>2</Subscript> films

Electrical conductivity, dielectric permittivity and mechanical hardness of the polycrystalline CeO₂ + xSm₂O₃ (x = 0, 10.9–15.9 mol %) films prepared by Electron Beam Physical Vapour Deposition (EB-PVD) and Ionic Beam Assisted Deposition, (IBAD), techniques were investigated in dependence on their structure and microstructure influenced by the deposition conditions, namely composition, deposition temperature and Ar⁺ ion bombardment. The electrical conductivity of doped ceria prepared without Ar⁺ ion bombardment and investigated by the impedance spectroscopy, IS, was found to be predominantly ionic one under the oxidizing atmosphere/low-temperature conditions and the higher amounts of Sm₂O₃ (>10 mol %) used. The bulk conductivity as a part of total measured conductivity was a subject of interest because the grain boundary conductivity was found to be ∼3 orders of magnitude lower than the corresponding bulk conductivity. Ar⁺ ion bombardment acted as a reducer (Ce⁴⁺ → Ce³⁺) resulting in the development of electronic conductivity. Dielectric permittivity determined from the bulk parallel capacitance measured at room temperature and the frequency of 1 MHz, similarly as the mechanical hardness measured by indentation (classical Vickers and Depth Sensing Indentation-DSI) techniques were also found to be dependent on the deposition conditions. The approximative value of hardness for the investigated films deposited on the substrate was estimated using a simple phenomenological model described by the power function HV = HV ₀ + aP ^b and compared with the so-called apparent hardness (substrate + investigated film) determined by the classical Vickers formula. Results obtained are analyzed and discussed.     

Cellulose scaffolds modulated synthesis of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> nanocrystals: preparation,characterization and properties

Magnetic Co₃O₄ nanoparticles were prepared by using microporous regenerated cellulose films as sacrificial scaffolds. The cellulose macromolecules and the porous structure of the films made them used as spatially confined reacting sites where Co(OH)₂ nanoparticles could be synthesized in situ. When the cellulose matrix was removed by sintering at 500 °C, Co₃O₄ nanoparticles were obtained. XRD and XPS indicated that the prepared nanoparticles were pure Co₃O₄ without any impurity. TEM and SEM images revealed that the particle size of the nanoparticles was smaller than 100 nm. The nanoparticles had weak ferromagnetic properties at 25 °C. Furthermore, the pronounced quantum confinement effects of the synthesized nanoparticles have been observed, the optical bandgap energies determined were about 1.92 ~ 2.12 and 2.74 ~ 2.76 eV for O²⁻ → Co³⁺ and O²⁻ → Co²⁺ charge-transfer processes, respectively. Furthermore, the resulted Co₃O₄ nanoparticles behaved stable electrochemical performance with promising applications in the electrode for lithium ion battery.     

Structure and electric properties of Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>-NaPO<Subscript>3</Subscript> glasses

The influence of the SO₄²⁻ ion on the temperature and concentration dependences of electric conductivity and the structure of sodium phosphate oxide glasses was studied. The increased electric conductivity of sulfate-phosphate glasses was explained by the formation of mixed sulfate-phosphate fragments with terminal SO₄²⁻ ions in the structure of glasses in the Na₂SO₄-NaPO₃ system. The dissociation energies of the sodium sulfate fragments are lower than those of pure oxide sodium phosphate structural units. As a result, the number of dissociated sodium ions increases, the activation energy of electric conductivity falls, and the conductivity (at 25°C) increases approximately 270-fold relative to the conductivity of NaPO₃. The arrangement of SO₄²⁻ ions in the structure was evaluated from the IR spectra of the glasses.     

Effect of sol temperature on the structure,morphology, optical and photoluminescence properties of nanocrystalline zirconia thin films

Transparent nanocrystalline zirconia thin films were prepared by sol–gel dip coating technique using Zirconium oxychloride octahydrate as source material on quartz substrates, keeping the sol at room temperature (SET I) and 60 °C (SET II). X-ray diffraction (XRD) pattern shows the formation of mixed phase [tetragonal (T) + monoclinic (M)] in SET I and a pure tetragonal phase in SET II ZrO₂ thin films annealed at 400 °C. Phase transformation from tetragonal to monoclinic was achieved in SET II film annealed at 500 °C. Atomic force microscopy analysis reveals lower rms roughness and skewness in SET II film annealed at 500 °C indicating better optical quality. The transmittance spectra gives a higher average transmittance >85% (UV–VIS region) in SET II films. Optical spectra indicate that the ZrO₂ films contain direct—band transitions. The sub- band in the monoclinic ZrO₂ films introduced interstitial O⁻defect states above the top of the valance band. The energy bandgap increased (5.57–5.74 eV) in SET I films and decreased (5.74–5.62 eV) in SET II films, with annealing temperature. This is associated with the variations in grain sizes. Photoluminescence (PL) spectra give intense band at 384 and 396 nm in SET I and SET II films, respectively. A twofold increase in the PL intensity is observed in SET II film. The “Red” shift of SET I films and “Blue” shift of SET II films with annealing temperature, originates from the change of stress of the film due to lattice distortions.     

Effect of annealing atmosphere on structural,optical and electrical properties of Al-doped Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O thin films

1 at.% Al-doped Zn_1−x Cd _x O (x = 0–8 at.%) thin films were prepared on glass substrates by sol–gel method. The codoping films retained the hexagonal wurtzite structure of ZnO, and showed preferential c-axis orientation. The effect of annealing ambient (in vacuum and nitrogen) on the optical and electrical properties of (Cd,Al)-codoped ZnO films were investigated using transmission spectra and electrical measurements. The transmittances of the codoping films were obviously degraded by vacuum annealing to 50–60 %, but enhanced to 70–80 % after nitrogen annealing. The carrier concentration and Hall mobility both increased, and resistivity decreased with narrowing band gap of Al-doped Zn_1−x Cd _x O, below different critical concentrations x = 4 % (in vacuum) and x = 6 % (in nitrogen). It is revealed that the conductivity is also improved by Cd doping along with band gap modification. The variations in optical and electrical properties are ascribed to both the changes of the crystallinity and concentration of oxygen vacancies under different ambient. In view of transmittance and conductivity, nitrogen annealing might be a more effective post-annealing way than vacuum annealing for our (Cd,Al)-codoped ZnO films to meet the requirements of transparent conducting oxide (TCO).