Chemical Solution Approach Research Articles

Exploring the energy storage capacity of the Pb1−xLaxHfO3 system by composition engineering

The increasing demands on the energy storage capacity of dielectric capacitors require the exploration of suitable dielectric material systems. In the present work, Pb1−xLaxHfO3 (x = 0, 0.1, 0.2, 0.3 and 0.4) films grown on Pt/Ti/SiO2/Si substrates were fabricated via a conventional chemical solution approach. The lanthanum substitution can result in enhanced electric breakdown strengths (EBDS) for all the compositions, varying from 2030.1 to 4162.7 kV/cm. The electrical properties and microstructure reveal that the antiferroelectric state gradually weakens or even disappears with the increase of La content. The Pb0.9La0.1HfO3 film presents an excellent energy storage performance, with recoverable energy density of 47.5 J cm−3 and energy efficiency of 60.0 %, thanks to the largest ΔP of 55.1 μC/cm2 and enhanced EBDS. Meantime, it exhibits excellent frequency and thermal stability over the studied frequency range (500 Hz-20 kHz) and wide temperature range (25–200 °C). The results shed light on that Pb0.9La0.1HfO3 film capacitor have potential for practical applications.

Artificially induced ferroelectric-like behavior in an antiferroelectric sandwich structure by interface engineering

Interface engineering is essential for achieving fascinating interfacial functionalities in a single all-oxide-interface-based device. In the present work, a sandwich structure (Pb0.94La0.06(Zr0.95Ti0.05)O3 (PLZT)/HfO2/ Pb0.94La0.06(Zr0.95Ti0.05)O3) was fabricated via a chemical solution approach. A distinct “ferroelectricity-like” behavior with high Pmax (∼ 80 μC/cm2) and Pr (∼ 36 μC/cm2) is demonstrated. The dielectric HfO2 thin layer presents a tetragonal symmetry structure, which stabilizes a slight distorted structure of the upper PLZT layer (PLZT(T)) with a= 4.19(9) Å, b= 4.10(6) Å, β ∼ 91.04˚. In PLZT(T), the ferroelectric (FE) phase is identified as the matrix embedded with a small amount of AFE nanodomains, while the bottom PLZT layer (PLZT(B)) exhibits typical AFE incommensurately modulated structures. The near-interface structures in both PLZT layers are characterized by ferroelectric polarizations with head-to-tail configuration across the heterointerface. Such discontinuous, downward polarizations support the accumulation of oxygen vacancies at the heterointerface that facilitate the local polarization enhancement. It is the combination effect of stable ferroelectric polarization in the PLZT(T) layer, interfacial oxygen vacancies and large surface to volume ratio that leads to the superior polarization performance of the antiferroelectric sandwich structure. It indicates that interface engineering is a feasible approach to manipulate the ferroic behavior.

Oxide Films and Nanoparticles for Lithium Ion Battery and Oxygen Electrocatalyst Applications

The global energy crisis coupling with the consumption of fossil fuels and the associated environmental issues, has stimulated extensive interest in searching for clean, efficient and sustainable energy storage and conversion systems. In this talk we are going to introduce a novel chemical solution approach for epitaxial thin film deposition and oxide nanoparticle network synthesis. The use of water soluable polymer to bind the metal ions has several advantages. The formation of covalent complexes between the lone pairs on the nitrogen atoms of the polymer and the metal cations make it possible to prepare almost any metal polymer precursor solutions. The unique chemistry and processing design of this technique deliver stable and homogeneous solutions at a molecular level that allows epitaxial growth of high-quality thin films and oxide nanoparticle network materials. Oxygen electrocatalysis, including both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), dominates the performance of the devices. However, the sluggish kinetics of these two reactions limits their performance. Therefore, development of non-precious metal-based oxygen electrocatalysts is greatly demanded. Metal oxides have attracted extensive interest as alternative electrocatalysts due to their low price and good endurance under relatively high temperature, which can be doped with a wide range of cations attributed to their flexible compositions and structures, leading to easy manipulation of their electrocatalytic properties. We study the nanoscale engineering of perovskite oxides and layered oxides in energy conversion/storage devices and focus on the electrode catalyst design and fabrication for boosting ORR and OER electrocatalysis.

V2O5 nanocrystals: Chemical solution synthesis, hydrogen thermal treatment and enhanced rate capability as cathode materials for lithium-ion batteries

Vanadium pentoxide (V2O5) is regarded as a promising cathode material for high-performance lithium-ion batteries (LIBs). In this study, V2O5 nanocrystals with an elongated plate-like morphology are prepared via a chemical solution approach that involves the hydrolyzation of vanadyl sulfate in alkaline solution. Oxygen vacancies are intentionally created by thermal treating the V2O5 samples under hydrogen-containing gases at different temperatures. Although the annealing process does not change the shape, morphology and crystalline structure of V2O5 nanocrystals, it does bring about a small amount of oxygen vacancies, as evidently from the results of XRD patterns and Raman spectra. The presence of oxygen vacancies has positive effects on the electrochemical properties. A higher initial discharge capacity, and excellent rate capability and cycling stability are observed on the oxygen vacancy-containing V2O5 samples. Especially, the sample annealed at 350 °C is found to have an initial capacity of 284 mAh g−1and the capacity still maintains at about 153 mAh g−1 even at 10 C. The combination of nanoscale dimension and oxygen vacancies in V2O5 nanocrystals presents a simple way to improve their rate capability and cycling stability for potential high-performance LIB applications.

Design, synthesis, microstructure and electrical properties of thermal-strained PZT films

The integration units with functional and structural material components have been developed largely recently. In the present study, 200 nm-thick polycrystalline PbZr0.52Ti0.48O3 (PZT) films with a dense columnar structure were grown on LaNiO3 (LNO) buffered heat-resistant steel substrates via a low-cost chemical solution approach. The behavior of the functional PZT films when combined with the structural steel was investigated mainly by TEM and electrical measurement. A large in-plane compressive stress was obtained in the PZT films due to the thermal expansion mismatch of about 88.2 % between the thin films and the steel substrates, which intensifies the orientation of the films toward c-axis. Sub-10 nm 90° nanodomains were alternately distributed in [001] grains which is beneficial to the piezoelectric performance, and the equivalent d33 value is ～44.4 pm V−1. A remnant polarization (Pr) of ～67.3μC/cm2 and a dielectric constant of ～425 were obtained. The enhanced electrical properties are associated with the stress-induced improved c-axis spontaneous polarization and crystal orientation in the hybrid system. This work may provide a theoretical basis for further integrating functional elements into metallic materials, which is valuable for covering the gap between academic research and industrial mass production.

Formation of composite nanostructures with an effective hydrazine sensor and their chemical approach

Abstract In this paper, the composite of nickel and cobalt was synthesized via nickel nitrate and cobalt nitrate hexahydrate as nickel cobalt oxide (NiCoO) processed via chemical solution approach. The chemicals such as the nickel nitrate hexahydrate, cobalt nitrate hexahydrate and sodium hydroxide were utilized to form a solution and it refluxed at ~90 °C for 60 min for formation of nanocomposite of NiCoO. Thereafter, the obtained composite of NiCoO was well characterized with the instruments such as X-ray diffraction pattern (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), fourier transform infrared (FT IR) and X-ray photoelectron spectroscopy (XPS) also with electrochemical data. The well crystalline formed nanoparticles have been employed as an electroactive material for high sensitive hydrazine sensor detection with glassy carbon electrode (GCE). The electro chemical characterization was analyzed with cyclic voltammetry (CV) data's at very low to high concentration (2 μL–2 mL/100 mL PBS), effect of scan rate was analyzed from 10 to 100 mVs−1 with NiCoO/GCE electrode. The proposed sensor and their stability are the promising features of the sensor.

Current progress in Cu 2 BaSn(S, Se) 4 thin film

The inexhaustible solar energy is regarded as a candidate to displace the diminishing fossil fuel resources and reduce greenhouse emissions. Photovoltaic and photoelectrochemical process provide a pathway for directly converting solar light into electricity power and clean hydrogen energy. It is significant to explore a promising and abundant material for utilization the solar energy. Cu2ZnSn(S, Se)4 has a direct bandgap, suitable bandgap (1.0–1.5 eV), high absorption efficient, which has been used as a absorbed layer in thin film solar cell achieving a power conversion efficiency of 12.6% and a photocathode gaining a photocurrent density of 13 mA/cm2. However, the close ionic sizes between Cu+ (0.91 A) and Zn2+ (0.88 A) in Cu2ZnSn(S, Se)4 leads to the antisite disorder and associated band tailing, and limits the performance improvement. According to the theoretical calculation, substituted the Cu or Zn with the large radius atom can efficiently reduce the antisite disorder. The large Ba substitutes Zn in Cu2ZnSn(S, Se)4 forming Cu2BaSn(S, Se)4, which can suppress the antisite defects. According to the Schockley-Queisser theory, the photocurrent density of the photocathode based on bare Cu2BaSn(S, Se)4 thin film is 14.5 mA/cm2 under AM 1.5G illumination and the maximum power conversion efficiency of the thin film solar cell based on a pure Cu2BaSn(S, Se)4 ( E g =2.0 eV) is 22%. Therefore, it has attracted a great deal of attentions in Cu2BaSn(S, Se)4 thin films. From a special perspective, this review summarizes the progress of Cu2BaSn(S, Se)4 thin films in recent years. First, we outline the physical properties of Cu2BaSn(S, Se)4. According to the experimental and theoretical results, it reveals that the Cu2BaSn(S, Se)4 has less cationic disordering and associated band tailing than that in Cu2ZnSn(S, Se)4, which indicates the Cu2BaSn(S, Se)4 will be a promising candidate to Cu2ZnSn(S, Se)4. Moreover, the Cu2BaSn(S, Se)4 has two crystal structures and the phase transition from trigonal ( P3 1 ) to orthorhombic ( Ama 2 ) with a increasing Se/(S+Se) ratio. Due to the phase transition, the bandgap decreases with an increasing Se/(S+Se) ratio, achieved a lowest bandgap, then the bandgap increases with an increasing Se/(S+Se) ratio. In other word, the bandgap of Cu2BaSn(S, Se)4 can be controlled by adjusted the Se/(S+Se) ratio. Meanwhile, the Cu2BaSn(S, Se)4 shows a direct bandgap which is beneficial to the performance of photoelectrical devices. Therefore, Cu2ZnSn(S, Se)4 will be an excellent semiconductor material in photoelectrical field. Second, the methods for preparing Cu2BaSn(S, Se)4 thin films is a hot topic. Here, we classified the methods for growing Cu2BaSn(S, Se)4 thin films to physical deposition approach and chemical solution approach. The advantages and disadvantages of the method are summarized in this review. It is worth to noting, the morphology of the thin films is related with the composition of Cu2BaSn(S, Se)4. Third, we summarized the application field of Cu2BaSn(S, Se)4 thin films. For example, the solar cells based on Cu2BaSn(S, Se)4 get a highest power efficiency conversion of 5.2% (total area 0.425 cm2) and the Cu2BaSn(S, Se)4 applied in photoelectrochemical electrode achieved a current-density of 12.08 mA/cm2 at 0 V vs. reversible hydrogen electrode. Finally, we conclude the prospective and challenge in the future.

Spontaneous cationic ordering in chemical-solution-grown La2CoMnO6 double perovskite thin films

Double perovskite oxides are of interest because of their electric, magnetic, and elastic properties; however, these properties are strongly dependent on the ordered arrangement of cations in the double perovskite structure. Therefore, many efforts have been made to improve the level of cationic ordering to obtain optimal properties while suppressing antisite defect formation. Here, epitaxial double perovskite La2CoMnO6 thin films were grown on top of (001)-STO oriented substrates by a polymer-assisted deposition chemical solution approach. Confirmation of the achievement of full Co/Mn cationic ordering was found by scanning transmission electron microscopy (STEM) measurements; EELS maps indicated the ordered occupancy of B–B′ sites by Co/Mn cations. As a result, optimal magnetic properties (Msat ≈ 6 µB/f.u. and Tc ≈ 230 K) are obtained. We show that the slow growth rates that occur close to thermodynamic equilibrium conditions in chemical solution methods represent an advantageous alternative to physical deposition methods for the preparation of oxide thin films in which complex cationic ordering is involved.

Structural, magnetic, optical, and magneto-optical properties of CoFe2O4 thin films fabricated by a chemical approach

Homogeneous, smooth, and partially transparent nanocrystalline thin films of CoFe2O4 were fabricated using a chemical solution approach with additional annealing for 2 h in a temperature range of 300 °C to 600 °C. Structural properties investigated by X-ray diffraction showed a single-phase spinel structure with a random crystallographic orientation for samples annealed above 400 °C. The ferromagnetic nature of prepared films was established from combined substrate with film hysteresis loops measured using a vibrating sample magnetometer. Optical and magneto-optical spectroscopic measurements revealed an improvement in the structural quality of the films after annealing up to 600 °C.

Nanorods of ZnO: An effective hydrazine sensor and their chemical properties

In this paper, ZnO nanorods (ZnONRs) have been synthesized via chemical solution approach. The chemicals such as the nitrate salt of zinc, hexamethylenetetramine and NaOH were utilized and the acquired solution was refluxed at ∼90 °C for 60 min for fabrication of nanorods. Thereafter, the obtained NRs were well characterized with the instruments such as X-ray diffraction pattern (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and Fourier transform infra-red (FTIR) spectroscopy also with electrochemical data. The well crystalline nanorods were used as an electrode material for to high sensitive hydrazine sensor detection with glassy carbon electrode (GCE). The cyclic voltammetry (CV) data's were analyzed from low (2μL/100 mL PBS) to high concentration (1–5 mL/PBS) of hydrazine with NRs/GCE electrode. The electrochemical impedance spectroscopy (EIS) was evaluated from 0 to 5 mL of solution at 4211 Z/ohm conditions. The proposed sensor and their stability are the promising features of the sensor.

Outstanding Piezoelectric Performance in Lead‐Free 0.95(K,Na)(Sb,Nb)O3‐0.05(Bi,Na,K)ZrO3 Thick Films with Oriented Nanophase Coexistence

AbstractLead‐free 0.95(K0.48Na0.52)(Nb0.95Sb0.05)O3‐0.05Bi0.5(Na0.82K0.18)0.5ZrO3 (KNSN‐BNKZ0.05) piezoelectric films with preferred crystal orientation and enhanced thickness are fabricated on silicon substrates from a chemical solution approach. Adequate K excess is introduced to obtain a single perovskite phase in the resulting thicker films. The effects of thickness, crystal orientation, and structure of the films on the performance are investigated. Outstandingly large effective piezoelectric strain coefficient up to 250 pm V−1 is demonstrated over a macroscopic scale using a laser scanning vibrometer in the [100]‐KNSN‐BNKZ0.05 film with an enhanced thickness of 2.7 µm, competitive to the benchmark oriented lead zirconate titanate films on silicon. Atomically resolved electron microscopy reveals the coexistence of oriented ferroelectric rhombohedral (R) and tetragonal (T) phases at the nanometer scale with gradual polarization rotation, which can lower the domain wall energy and facilitate the large piezoelectric response. The increased film thickness reduces the in‐plane mechanical clamping to enable more free deformation in the thickness direction and improve domain wall mobility, both further contributing to enhanced piezoelectric response.

Textured WO3 and WO3:Mo films deposited from chemical solution on stainless steel

Tungsten trioxide (WO3) and molybdenum-doped tungsten trioxide (WO3:Mo) films were deposited on stainless steel surface by a chemical aqueous solution approach using dip-coating technique. The deposited 5, 10 and 15-layer films were homogeneous and continuous. The surface morphology and crystallinity of the produced films were dependent on the metal cation species and concentration of PVA in the solution. FE-SEM analysis revealed the formation of textured WO3 film surfaces having spike-like nanostructures. The values of the static water contact angle measured on the film surface showed that deposited WO3 films can exhibit both hydrophilic and hydrophobic nature, while WO3:Mo films showed hydrophilic behavior. Tribological properties of the deposited films were evaluated in deionized water. All three coatings retained a lubricating layer much better than original steel, demonstrating major reduction in friction and wear. Particularly effective were PVA-free WO3 films, whose friction coefficient stayed under 0.2 for over 2000 cycles. Excellent tribological, hydrophobic and hydrophilic properties along with simple deposition methods suggest very promising potential of WO3 and WO3:Mo coatings in industrial applications.

Enhanced Metal-Insulator Transition Performance in Scalable Vanadium Dioxide Thin Films Prepared Using a Moisture-Assisted Chemical Solution Approach.

Vanadium dioxide (VO2) is a strong-correlated metal-oxide with a sharp metal-insulator transition (MIT) for a range of applications. However, synthesizing epitaxial VO2 films with desired properties has been a challenge because of the difficulty in controlling the oxygen stoichiometry of VO x, where x can be in the range of 1 < x < 2.5 and V has multiple valence states. Herein, a unique moisture-assisted chemical solution approach has been developed to successfully manipulate the oxygen stoichiometry, to significantly broaden the growth window, and to significantly enhance the MIT performance of VO2 films. The obvious broadening of the growth window of stoichiometric VO2 thin films, from 4 to 36 °C, is ascribed to a self-adjusted process for oxygen partial pressure at different temperatures by introducing moisture. A resistance change as large as 4 orders of magnitude has been achieved in VO2 thin films with a sharp transition width of less than 1 °C. The much enhanced MIT properties can be attributed to the higher and more uniform oxygen stoichiometry. This technique is not only scientifically interesting but also technologically important for fabricating wafer-scaled VO2 films with uniform properties for practical device applications.

Surfactant-free synthesis of ZnO micro/nanoflowers with efficient photocatalytic antibacterial performance

Flower-like ZnO micro/nanostructures were prepared via a simple and surfactant-free chemical solution approach. X-ray diffraction findings showed that the prepared ZnO product was highly crystalline with hexagonal wurtzite structure. The band gap energy of ZnO sample was measured to be 3.32eV via an optical reflectance spectrum. The flower-like morphological features of ZnO micro/nanostructures were witnessed through transmission electron microscopy and field-emission scanning electron microscopy. The prepared ZnO product revealed an efficient visible light photocatalytic antibacterial activity against Escherichia coli, which could be due to its special structure feature. The Ag/ZnO composite was also prepared and displayed improved photocatalytic antibacterial activity after decorating noble metal on the surface of ZnO nanoflowers.

An efficient organic solvent-free solution-processing strategy for high-mobility metal chalcogenide film growth

One of the primary challenges for high-quality metal chalcogenide film growth by a chemical solution approach is to avoid the use of volatile/hazardous organic solvents during the fabrication processes.

Scaling Effects in Sodium Zirconium Silicate Phosphate (Na1+xZr2SixP3−xO12) Ion‐Conducting Thin Films

Preparation of sodium zirconium silicate phosphate (NaSICon), Na1+xZr2SixP3−xO12 (0.25 ≤ x ≤ 1.0), thin films has been investigated via a chemical solution approach on platinized silicon substrates. Increasing the silicon content resulted in a reduction in the crystallite size and a reduction in the measured ionic conductivity. Processing temperature was also found to affect microstructure and ionic conductivity with higher processing temperatures resulting in larger crystallite sizes and higher ionic conductivities. The highest room temperature sodium ion conductivity was measured for an x = 0.25 composition at 2.3 × 10−5 S/cm. The decreasing ionic conductivity trends with increasing silicon content and decreasing processing temperature are consistent with grain boundary and defect scattering of conducting ions.

Controlled synthesis of monodisperse α-calcium sulfate hemihydrate nanoellipsoids with a porous structure.

We report a facile and green chemical solution approach to synthesize monodisperse α-calcium sulfate hemihydrate (α-HH) nanoellipsoids with a length of 600 nm and a width of 300 nm by simply mixing Ca(2+) and SO4(2-) glycerol-water precursor solutions in the presence of Na2EDTA. The α-HH nanoellipsoid is formed through a Na2EDTA-mediated self-assembly of small primary building blocks (α-HH domains: ∼14 nm). The study on the morphological evolution of α-HH reveals that the controlled synergy of supersaturation (precursor concentration) and Na2EDTA is crucial for the development of α-HH into nanoellipsoids. Further thermal annealing of the nanoellipsoid could make the α-HH domains transit into calcium sulfate anhydrites and grow up, generating the gaps between them and resulting in a porous structure. This work paves a new way for preparing high-quality α-HH nanoellipsoids with a monodisperse nanosize and a porous structure, promising their future application in many fields such as biomedicine.

Effect of PbO excess on the microstructure, dielectric and piezoelectric properties, and energy-storage performance of Bi(Ni1/2Ti1/2)O3–PbTiO3 thin films

Ferroelectric Bi(Ni1/2Ti1/2)O3–PbTiO3 (BNT–PT) thin films near the morphotropic phase boundary (MPB) with different amount of excess lead (0, 10, and 20%) were successfully deposited onto Pt(111)/Ti/SiO2/Si substrates via a chemical solution approach. The effects of excess lead on the microstructure, dielectric and piezoelectric properties, and energy-storage performance of the thin films were investigated in detail. X-ray diffraction results revealed that the films showed an increasing (100)-orientation with an increasing amount of excess lead. Dielectric, ferroelectric, and current–voltage measurements showed that the films with more excess lead exhibited an enhanced dielectric constant and greater back-switch behavior, while the smaller leakage current density. As a result, the energy-storage density was also markedly improved from 22.8 to 50.2 J/cm3 under an electric field of 2250 kV/cm. The effective piezoelectric constant d33 increased from 41.5 to 70.1 pm/V with increasing excess lead from 0 to 20%.

(Invited) Fabrication and Dielectric Properties of BaTiO3 Thin Films on Polycrystalline Ni Foils

The BaTiO3 (BTO) thin films were deposited on polycrystalline Ni foils using a chemical solution approach. We show that the interface between the BTO film and the Ni foil plays a critical role in determining the dielectric and magnetoelectric (ME) properties of this flexible assembly. A pretreatment process of nickel foils with hydrogen peroxide (H2O2) solution has been conducted to form thin nickel oxide layers on the surfaces for the growth of BTO films. Both the concentration of H2O2 solution and the pretreated time were found to strongly affect the dielectric constant of BTO films, which is likely to be related to the evolution of nickel oxide at the interface during the growth of BTO films. The growth dynamics was systematically studied to optimize the single phase BTO films with good dielectric properties. Our results have demonstrated that not only a well-controlled interface between the BTO film and the Ni substrate can be achieved, but also an good dielectric and ME performance can be accomplished.

(Invited) Fabrication and Dielectric Properties of BaTiO3 Thin Films on Polycrystalline Ni Foils

The BaTiO3 (BTO) thin films were deposited on polycrystalline Ni foils using a chemical solution approach, polymer-assisted deposition. We show that the interface between the BTO film and the Ni foil plays a critical role in determining the dielectric and ferroelectric properties of this flexible assembly. A pretreatment process of nickel foils with hydrogen peroxide (H2O2) solution has been conducted to form thin nickel oxide layers on the surfaces for the growth of BTO films. A rapid thermal post-annealing in oxygen would also strongly affect the electric properties of the as-prepared thin films. The growth dynamics was systematically studied to optimize the single phase BTO films with good dielectric and ferroelectric properties.