Piezoelectric enhancement and vacancy defect reduction of lead-free Bi0.5Na0.5TiO3-based thin films

To explore new lead-free piezoelectric materials that is both environmentally friendly and healthy to provide the possibility for material selection for microelectromechanical systems. Lead-free piezoelectric (1-x)(0.8Bi_0.5Na_0.5TiO₃-0.2Bi_0.5K_0.5TiO₃)-xBi(Ni_0.5Zr_0.5)O₃ thin films (abbreviated as BNT-BKT-xBNZ) (x=0.00, 0.01, 0.02, 0.03, 0.04) were prepared on Pt(111)/Ti/SiO₂/Si substrates by a sol-gel method. Impacts of Bi(Ni_0.5Zr_0.5)O₃ content on the microstructure, dielectric, ferroelectric, and piezoelectric properties were also investigated detailedly. It found that the Bi(Ni_0.5Zr_0.5)O₃ composition had a great influence on the increase of relaxor and the decrease of the oxygen vacancies, which is influential to the promotion of thin-film properties. Thin-film of BNT-BKT-0.02BNZ showed the optimum electrical properties with the polarization of 40.27 μC/cm², dielectric constants of 477 and effective inverse piezoelectric coefficient reach up to 125.9 p.m./V. Results revealed that the BNT-BKT thin films with 0.02 mol% Bi(Ni_0.5Zr_0.5)O₃-doped are a kind of lead-free piezoelectric materials with superior manifestations with a great development prospect for applications.     

Preparation and characterization of multicomponent porous materials prepared by the sol-gel process

An experimental strategy was developed to obtain transparent Si-Al-Ti-Ni-Mo and Si-Zr-Ti-Ni-Mo sols via the sol-gel process. The sol was prepared from Si(OEt)₄ (TEOS), Al(OBu^s)₃ (OBu^s: C₂H₅CH(CH₃)O), Ti(OEt)₄ (OEt: OCH₂CH₃), Zr(OPrⁿ)₄ (OPrⁿ: OCH₂CH₂CH₃). In both cases nickel nitrate hexahydrate (Ni(NO₃)₂ · 6H₂O) and ammonium heptamolybdate tetrahydrate ((NH₄)₆Mo₇O₂₄ · 4H₂O) were the Ni and Mo sources, respectively. The sols were characterized by Fourier Transform Infrared Spectroscopy (FTIR). Assignments of the simultaneous formation of the Si-O-Al, Si-O-Ti, Si-O-Ni, and Si-O-Zr bonds were done. The sols were polymerized at room temperature (293 K) to obtain gels, and these were dried at 423 K and calcined at 573, 853 and 893 K in air. The characterization techniques used were small-angle X-ray scattering (SAXS), X-ray diffraction (XRD), scanning electron microscopy (SEM), and ²⁹Si and ²⁷Al magic angle spinning nuclear magnetic resonance (MAS NMR). The density of the solids was measured following ASTM method D-4892 and the porosity and surface area were determined by N₂ adsorption/desorption isotherms. The corresponding average pore diameters were evaluated using the BJH, HK, and DA methods.     

Catalytic Fabrication of SiC/SiO2 coated graphite and its behaviour in Al2O3–C castable systems

SiC/SiO₂ coated graphite was prepared via a combined sol-gel coating and catalytic conversion route, using graphite flake and tetraethyl orthosilicate as the starting materials, and Fe(NO₃)₃·9H₂O as the catalyst precursor. X-ray diffraction analysis and microstructural examination revealed that a homogeneous coating comprising SiC and cristobalite (SiO₂) and covering the whole surface of graphite was formed. As prepared SiC/SiO₂ coated graphite exhibited better oxidation resistance and water wettability than its uncoated counterpart. Also, oxidation resistance and slag corrosion resistance of a model Al₂O₃–C castable using coated graphite as a carbon source were better than in the case of its counterpart using uncoated graphite.     

Preparation and properties of (Ba0·7Sr0·3)TiO3 powders and thin films using precursor solutions formed from alkoxide-hydroxide

(Ba_0·7Sr_0·3)TiO₃ powders and thin films were prepared using alkoxide-hydroxide route. Solutions of Ba and Sr hydroxides dissolved in methanol were reacted with Ti-isopropoxide under conditions of stirring at room temperature for 15 h, and then dried under reduced pressure at ≦40°C to prepare precursors of (Ba_0·7Sr_0·3)TiO₃ powder. The amorphous precursors were hydrolyzed at 100°C by introducing nitrogen gas containing water vapor. The hydrolyzed products were crystalline nanosize powders of (Ba_0·7Sr_0·3)TiO₃. As-hydrolyzed (Ba_0·7Sr_0·3)TiO₃ powders showed a good crystallinity with cubic phase. (Ba_0·7Sr_0·3)TiO₃ thin films were also successfully prepared at 650°C on Pt/Ti/SiO₂/Si substrates from precursor solutions obtained by the reaction of alkoxide with hydroxides. The (Ba_0·7Sr_0·3)TiO₃ thin films exhibited the microstructure with fine grains as small as 20–60 nm. The dielectric constants of the thin films ranged from 600 to 800 at room temperature.     

The underpotential deposition of Bi2Te3−ySey thin films by an electrochemical co-deposition method

Bi₂Te_3−ySe_y thin films were grown on Au(1 1 1) substrates using an electrochemical co-deposition method at 25 °C. The appropriate co-deposition potentials based on the underpotential deposition (upd) potentials of Bi, Te and Se have been determined by the cyclic voltammetric studies. The films were grown from an electrolyte of 2.5 mM Bi(NO₃)₃, 2 mM TeO₂, and 0.3 mM SeO₂ in 0.1 M HNO₃ at a potential of −0.02 V vs. Ag|AgCl (3 M NaCl). X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were employed to characterize the thin films. XRD and EDS results revealed that the films are single phase with approximate composition of Bi₂Te_2.7Se_0.3. SEM studies showed that the films are homogeneous and have micronsized granular crystallites.     

Altering the wettability of bitumen-treated glass surfaces with ionic surfactants

The abilities of three ionic surfactants—sodium methylnaphthalene sulfonate (SMNS), sodium dodecyl sulfate (SDS), and cetyl trimethylammonium bromide (CTAB)—to alter the wettability of bitumen-treated glass surfaces was examined. Surface wettability was characterized by contact angles, and all measurements were carried out under alkaline conditions by having sodium carbonate (Na₂CO₃) dissolved in the aqueous phase. It was found that Na₂CO₃ alone could slightly increase the hydrophilcity of bitumen-treated glass surfaces. With surfactants added to the system, it was demonstrated that SMNS and SDS (both anionic surfactants) were much more effective in enhancing the water wettability of bitumen-treated glass in comparison to CTAB (a cationic surfactant). X-ray photoelectron spectroscopy (XPS) analyses were also conducted to determine the functional groups and relative mass concentrations of various elements on the glass substrates. Based on these results, we speculate that most or all of the adsorbed hydrocarbon material could be removed from a glass substrate through synergistic effects between sodium carbonate, which provides the alkaline condition, and anionic surfactants, which likely interacted with adsorbed cationic materials. This resulted in dramatic alteration in the wettability of bitumen-treated glass surfaces—from oil-wet to water-wet.     

Investigation of Optimal Growth Conditions of La0.7Sr0.3MnO3–Bi2Sr2Ca1Cu2O8 Heterostructures

The deposition conditions of less explored La_0.7Sr_0.3MnO₃ (LSMO) and Bi₂Sr₂Ca₁Cu₂O₈ (Bi‐2212) heterostructures are investigated in terms of two different deposition orders. One is in the order of Bi‐2212/LSMO and the other is LSMO/Bi‐2212. The experimental results indicate the metal‐insulator transition (T_MI) and Curie temperature (T_Curie) of LSMO as well as the superconducting critical transition (T_C) of the Bi‐2212 to be very sensitive to the order of deposition. In Bi‐2212/LSMO, due to factors such as strain, roughness, and degree of oxygenation, superconductivity is not stabilized to interact with LSMO. Whereas the LSMO/Bi‐2212 order of deposition displays both superconductivity and ferromagnetic behavior for a single post annealing condition. In LSMO/Bi‐2212, depositing Bi‐2212 as a top layer and post annealing in air is crucial to achieve optimal carrier concentration for exhibiting high T_C.     

Fabrication and function examination of PZT-based MEMS accelerometers

In this study, a hybrid sol-gel method was used to fabricate Pb(Zr_0.52Ti_0.48)_0.98Nb_0.02O₃ (PNZT) piezoelectric thick films. By preparing Pb(Zr_0.52Ti_0.48)_0.98Nb_0·02O₃ sol-gel solutions and mixing them with PZT-5A piezoelectric powders, therefore, the thickness of single layer coating can be increased and reduce the risk of film cracks. The proposed PNZT films have the dielectric constant of 1750, dielectric loss of 0.063, remnant polarization of 58 μC/cm², and d₃₃ of 133 p.m./V. Piezoelectric cantilever beam MEMS accelerometers were then designed, simulated and fabricated via photolithography methods on Si substrates. The sensitivity and natural frequency of the cantilever beam accelerometer are 16.8 mV/g and 200Hz, respectively. Finally, a cantilever beam accelerometer is successfully applied for the server hard-drive fault detection.     

Effect of the origin of ZnO nanoparticles dispersed in polyimide films on their photoluminescence and thermal stability

Polyimide (PI) films containing dispersed ZnO nanoparticles were prepared from both zinc nitrate hexahydrate (designated as Zn(NO₃)₂/PI) and ZnO nanoparticles, 2‐nm average primary size (ZnO/PI). This work shows how the origin of ZnO affects both the photoluminescence and thermal decomposition of the film. The presence of ZnO derived from Zn(NO₃)₂·6H₂O was confirmed by X‐ray diffraction technique. The fluorescent intensities from Zn(NO₃)₂/PI and ZnO/PI were much higher than that from pure PI films. When the ZnO concentration exceeded a certain saturation level, the emission intensity decreased due to the undesirable aggregation of ZnO. At the same concentration, ZnO/PI exhibited higher emission intensity than Zn(NO₃)₂/PI. All samples prepared under nitrogen emitted higher intensity than their counterparts prepared under argon. The ZnO/PI film was thermally more stable than the Zn(NO₃)₂/PI one. From TEM images of 117.6 mol% ZnO/PI films, the ZnO aggregates, whose average size was 17–90 nm, were well distributed throughout the film but poorly dispersed in nanometer range. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Nanostructured α- and β-cobalt hydroxide thin films

A new perspective in the use of electrochemical methods to deposit cobalt hydroxide thin films is presented. Ordered arrays of α-Co(OH)₂ (hydrotalcite-like (Co-HT)) and β-Co(OH)₂ nanoparticles were synthesized on transparent conductive oxide (TCO) substrates by localized cathodic electrogeneration of hydroxyl via the reduction of NO₂⁻ (or NO₃⁻) ion precursors in solution containing Co²⁺ in very low concentration. The thin films, analyzed by X-ray diffraction and scanning electron microscopy were found to be composed of vertically oriented platelets with the crystallographic c-axis parallel to the substrate surface. Turbostratic disorder was not observed in the films. UV/Vis spectra and thermal gravimetric analyses (TGA) indicated distinct variation between the Co-HT structures. Films deposited at 60 °C using a nitrite precursor generated uniform, vibrant-green mixed-valence Co-HT (Co²⁺/Co³⁺). Nitrate precursors yielded a “hydroxyl-deficient” Co-HT (Co²⁺ only). Films deposited at 95 °C in nitrate solution yielded β-Co(OH)₂. The films obtained in presence of nitrite were thicker than those obtained in nitrate. They were formed of β-Co(OH)₂ and contained traces of Co-HT.     

Effect of PbTiO3 seed layer on the orientation behavior and electrical properties of Bi(Mg1/2Ti1/2)O3–PbTiO3 ferroelectric thin films

High Curie-temperature 0.63Bi(Mg_1/2Ti_1/2)O₃–0.37PbTiO₃ (BMT–PT) films were fabricated on Pt(111)/Ti/SiO₂/Si substrates by the sol–gel spin-coating method. The oriented growth behavior of thin films was controlled by introducing a PT seed layer onto the platinum electrode surface. The effect of the annealing method of the PT seed layer on the orientation behavior and electrical properties of BMT–PT films was investigated. It was found that BMT–PT thin film exhibits higher (100) orientation degree when the PT seed layer was treated by rapid thermal annealing. The dielectric permittivity increases while the remanent polarization and coercive field decrease with increasing the (100) orientation degree. These results were explained according to the relationship between the preferential orientation and the spontaneous polarization directions of the films.     

Surfactant-Induced Wettability Alteration of Oil-Wet Sandstone Surface: Mechanisms and Its Effect on Oil Recovery

Different analytical methods were utilized to investigate the mechanisms for wettability alteration of oil-wet sandstone surfaces induced by different surfactants and the effect of reservoir wettability on oil recovery. The cationic surfactant cetyltrimethylammonium bromide (CTAB) is more effective than the nonionic surfactant octylphenol ethoxylate (TX-100) and the anionic surfactant sodium laureth sulfate (POE(1)) in altering the wettability of oil-wet sandstone surfaces. The cationic surfactant CTAB was able to desorb negatively charged carboxylates of crude oil from the solid surface in an irreversible way by the formation of ion pairs. For the nonionic surfactant TX-100 and the anionic surfactant POE(1), the wettability of oil-wet sandstone surfaces is changed by the adsorption of surfactants on the solid surface. The different surfactants were added into water to vary the core surface wettability, while maintaining a constant interfacial tension. The more water-wet core showed a higher oil recovery by spontaneous imbibition. The neutral wetting micromodel showed the highest oil recovery by waterflooding and the oil-wet model showed the maximum residual oil saturation among all the models.     

Synthesis and ferroelectric investigations of poly(vinylidene fluoride‐co‐hexafluoropropylene)‐Mg(NO3)2 films

The free‐standing, flexible, and ferroelectric films of poly(vinylidenefluoride‐co‐hexafluoropropylene) [P(VDF‐HFP)] were prepared by spin coating method. The ferroelectric phase of the films was enhanced by adding magnesium nitrate Mg(NO₃)₂ in different wt % as the additive during the film fabrication. The effects on the structural, compositional, morphological, ferroelectric, dielectric, and leakage current behaviors of the films due to the addition of salt were analyzed. Based on the X‐ray diffraction (XRD) patterns and Fourier Transform Infrared (FTIR) spectra, it is confirmed that the addition of Mg(NO₃)₂ promotes the electroactive β phase that induces the ferroelectric property. The fiber‐like topography of the films exhibits a nodule‐like structure, and the roughness of the films increases by the addition of Mg(NO₃)₂. The ferroelectric studies show the higher polarization values for the composite films than that of the plain P(VDF‐HFP) film. The Piezo‐response force microscope images also confirm the domain switching behavior of the samples. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44008.     

Sono-assisted Synthesis of MgAl-layered Double Hydroxide Nanosheet/multiwalled Carbon Nanotube Filler for the Fabricating of L-isoleucine Amino Acid Based Polymer Nanocomposites

Hybrid of acid functionalized multiwalled carbon nanotubes and layered double hydroxides were prepared by coprecipitation reaction of the Al(NO₃)_3·9H₂O, Mg(NO₃)_2·6H₂O, and acid functionalized multiwalled carbon nanotubes under ultrasonic irradiation. An optically active amino acid containing poly(amide-imide) was synthesized by the direct polycondensation reaction of the N,N′-(pyromellitoyl)-bis-L-isoleucine diacid and diamine using molten tetra-n-butylammonium bromide. These three-dimensional nanofillers were used as reinforcing agent to enhance the performance of chiral poly(amide-imide). The structure and morphology of the hybrid materials were confirmed by Fourier transformed infrared spectroscopy, X-ray diffraction, field emission and transmission electron microscopy, and thermogravimetry analysis techniques.     

Novel bismuth ferrite nanopowder prepared by polyethylene glycol-assisted two-step solid-state reaction: Synthesis and magneto-optical properties

In this study, a bismuth ferrite (BiFeO₃) nanopowder was synthesized by combining Bi(NO₃)₃·5H₂O, Fe(NO₃)₃·9H₂O, and NaOH raw materials in the presence of polyethylene glycol (PEG) with varying polymerization degrees (i.e. PEG200, PEG400, PEG600, and PEG10000). The synthesis process was carried out by room-temperature solid-state reaction followed by subsequent secondary solid-state reaction at 550 °C. The results suggested a significant influence of PEG polymerization degree on the morphology and size of the as-synthesized products. The grain size decreased after the introduction of PEG but increased with the polymerization degree. The vibrating-sample magnetometry data revealed PEG400 and PEG600 with obvious room-temperature ferromagnetism properties. In UV–Vis spectroscopy, the absorption edge exhibited a blue shift as the polymerization degree of PEG rose. In sum, BiFeO₃ nanopowder possessed room-temperature ferromagnetism, thereby suitable photocatalyst for wastewater treatment and environmental purification with convenient recycling and substantial economic value.     

Facile fabrication of micro-patterned LSMO films with unchanged magnetic properties by photosensitive sol-gel method on LaAlO3 substrates

We propose here a facile and inexpensive photosensitive sol-gel method to fabricate micro-patterned La_0.67Sr_0.33MnO₃ (LSMO) films with c-axis orientation on (001) LaAlO₃ (LAO) single crystal substrates. The photosensitive LSMO sol-gel was first prepared using methanol as solvent, strontium acetate, manganese acetate and lanthanum nitrate as precursors, and 2,2'-Bipyridyl (Bpy) as chelating modifier. The sol-gel was photosensitive and was used to fabricate micro-patterned LSMO films directly in the absence of any photoresist. The as-prepared micro-patterned films exhibited regular microarray structure with smooth surface and clear edge. We also investigated the magnetic properties of LSMO films on LAO substrates. The overlapping of the magnetic momentum vs. temperature (M-T) curves as well the overlapping in the magnetic hysteresis loops of the micro-patterned and un-patterned LSMO films suggests that the photosensitive sol-gel method would be a promising technique to fabricate micro-patterned LSMO films without disturbing the original structure and functional properties.     

Synthesis and microstructural characterization of Bi12SiO20 (BSO) thin films produced by the sol–gel process

We have produced Bi₁₂SiO₂₀ (BSO) thin films using the sol–gel process. The stable sol was synthesized using Bi(NO₃)₃·5H₂O and Si(OC₂H₅)₄ (TEOS) as the precursors, acetic acid and 2-ethoxyethanol as the solvents, and ethanolamine as the stabilizer. The stability of the solution, which depends on the concentration and the R_h value (R_h = [H₂O]/[M]), directly affects the microstructure of the BSO thin film. We determined that the optimal concentration for the preparation of BSO thin films is 0.76 M. The influences of the substrates, the annealing temperature, the concentration and the R_h = value of the solution on the microstructure of the Bi₁₂SiO₂₀ thin films were investigated. X-ray diffraction (XRD) showed that the Bi₁₂SiO₂₀ starts to form at 500 °C and that single-phase Bi₁₂SiO₂₀ polycrystalline thin films are formed at 700 °C. The coated films were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM).     

Hydrolysis to the first dumbbell-like high-nuclearity bismuth-oxo cluster [Bi12(μ3-OH)4(μ2-OH)2(μ3-O)8(μ4-O)2(NO3)6]4+: Synthesis,structure and spectroscopic characterizations

The first dumbbell-like high-nuclearity bismuth-oxo cluster [Bi₁₂(μ₃-OH)₄(μ₂-OH)₂(μ₃-O)₈(μ₄-O)₂(NO₃)₆](NO₃)₄ · 6H₂O was obtained by diffusing ethanol into the hydrolysate of Bi(NO₃)₃ aqueous solution. The dumbbell consists of two Bi–O bonds as the handle and two [Bi₆(μ₃-OH)₂(μ₂-OH)(μ₃-O)₄(μ₄-O)] subunits as the bells. The bell can be regarded as a piercing bracelet-like ring consisted of six edge-sharing tetragons with one cross section enveloped by one μ₃-O linking three Bi(III) atoms and the other connected by one μ₂-O as a open cover. The structure is further stabilized by the interactions of Bi⋯Bi, Bi⋯O and hydrogen bondings. The optical gap of 2.85 eV suggests that the title compound behaves as semiconductors. The title compound features a blue fluorescence at 441 nm, which is assigned to ¹P₁–¹S₀ and ³P–¹S₀ transitions from the s² electron of Bi³⁺ cation.     

Influence of a high-frequency field on the formation of photosensitive thin-film materials synthesized by the sol-gel method

This paper reports on the results of investigations of the possibility of applying a high-frequency field for the formation of thin-film coatings from sols based on an aqueous-alcoholic solution of tetraethoxysilane, lead nitrate Pb(NO₃)₂, and selenious acid H₂SeO₃ with the use of the centrifugation method. A comparison is made of the data obtained from differential thermal analysis, X-ray powder diffraction analysis, optical microscopy, and atomic-force microscopy of the composites and thin-film coatings formed under thermal and microwave treatment. It is demonstrated that the application of high-frequency fields makes it possible to activate the physicochemical processes and to expand the range of use of the sol-gel technology for the formation of thin-film coatings on dielectric materials under the conditions which exclude a strong thermal effect.     

Wettability of amorphous and nanocrystalline Fe<Subscript>78</Subscript>B<Subscript>13</Subscript>Si<Subscript>9</Subscript> substrates by molten Sn and Bi

The wettability of amorphous and annealing-induced nanocrystalline Fe₇₈B₁₃Si₉ ribbons by molten Sn and Bi at 600 K was measured using an improved sessile drop method. The results demonstrate that the structural relaxation and crystallization in the amorphous substrates do not substantially change the wettability with molten Bi because of their invariable physical interaction, but remarkably deteriorate the wettability and interfacial bonding with molten Sn as a result of changing a chemical interaction to a physical one for the atoms at the interface.