Effect of Y doping on transport properties of La0.8Sr0.2MnO3 polycrystalline ceramics

In this study, La_0.8-xY_xSr_0.2MnO₃ (LYSMO) polycrystalline ceramics were prepared by means of sol-gel technique using methanol as solvent. X-ray diffraction (XRD) showed all samples to possess standard perovskite structure. Scanning electron microscopy (SEM) revealed samples with high compactness and grain size from 27.80 to 29.73 μm. Resistivity–temperature tests indicated sharp metal-insulator transition behavior of all samples accompanied by rapid transformation from ferromagnetism to paramagnetism (FM-PM). As Y³⁺ doping amounts rose, radius of A-site ions decreased, metal-insulator transition temperature (T_p) of polycrystalline samples shifted to lower temperatures, and resistivity increased. Temperature coefficient of resistance (TCR) and magnetoresistance (MR) were affected by introduction of Y³⁺. At x = 0.06, peak TCR and peak MR reached 4.85% K⁻¹ and 52.34%, respectively. Using double exchange (DE) interaction mechanism, electric transport performances of as-prepared ceramics were explained. These findings look promising for future applications of LYSMO materials in magnetic devices and infrared detectors.     

Enhanced conductance properties of UV laser/RTA annealed Al-doped ZnO thin films

Thin films comprising 0.5 mol% aluminum-doped zinc oxide (AZO) were prepared on glass substrates by a spin-coating method for transparent conducting oxide (TCO) applications. UV laser was selected for the annealing of AZO thin films, due to the well matched energy bandgap between UV laser and AZO films. After the rapid thermal annealing (RTA) process, post UV laser annealing was carried out by varying the scan speed of the laser beam, and the effects of laser annealing on the structural, morphological, electrical, and optical properties were analyzed. The results indicated that UV laser annealing based on various scan speeds affects the microstructure, sheet resistance, and optical transmittance of the AZO thin films, compared with those of the only RTA processed thin films. X-ray diffraction (XRD) analysis showed that all films that preferentially grew normally on the substrate had a (002) peak. The optical transmittance spectra of the laser/RTA annealed AZO thin films exhibited greater than 83% transmittance in the visible region. Also, the sheet resistance (1.61 kΩ/sq) indicated that optimized UV laser annealing after the RTA process improves film conductance.     

WO3/La0.8Pb0.2FeO3 perovskite heterostructure for highly active and selective hydrogen sulfide detection

In this study, tungsten oxide (WO₃) nanofibers were prepared using electrospinning technology and combined with La_0.8Pb_0.2FeO₃ (LPFO) perovskite materials to form a heterostructure film, and then used to evaluate the potential as a gas sensing material. The results show that the pure WO₃ nanofiber gas sensor has an excellent sensing effect on nitrogen dioxide (NO₂) and hydrogen sulfide (H₂S), and the WO₃/LPFO heterostructure film gas sensor still has a high response to H₂S, but the response to NO₂ is suppressed. This WO₃/LPFO heterostructure film gas sensor greatly improves the gas selectivity, making the selectivity more specific. The WO₃/LPFO heterostructure film gas sensor exhibits excellent gas selectivity for H₂S gas, the optimal operating temperature is 175 °C, and the response is about 89.5% under 1.25 ppm H₂S gas.     

Electro-optic properties of Ba0.8Sr0.2TiO3 thin film

Electro-optic properties of Ba_0.8Sr_0.2TiO₃ (BST) film with a thickness of 1 μm deposited on the MgO (001) substrate by the rf sputtering have been studied. Structural features of the film were identified by X-ray diffraction method. It was shown, that the BST film exhibited a predominantly linear EO behavior under the applied static electric field, that have been explained according to the strong compressive stresses in the film. The polarization distribution across the gap between the electrodes when electric field is applied was also investigated experimentally and calculated. The linear EO coefficient of Ba_0.8Sr_0.2TiO₃ film with a thickness of 1 μm film was found to be r_c = 99.4 p.m./V, that is promising for various EO applications, for example, high performance EO modulator.     

Influence of interface structure on microstructure and dielectric properties of bismuth magnesium niobate thin films

Bismuth magnesium niobate (Bi_3/2MgNb_3/2O₇, BMN) thin films were prepared on bare SiO₂/HR-Si and Pt/TiO₂/SiO₂/HR-Si substrates by using sol-gel spin coating technique followed by rapid thermal annealing process. The influence of the interface on crystalline structure and tunable dielectric properties of the two types of BMN films were investigated. It was found that the BMN films prepared on SiO₂/Si substrate with a BMN/SiO₂ interface structure had higher orientation and better crystallinity. The deposited BMN thin films with a BMN/SiO₂ interface structure exhibited superior tunability of 52.5%, while it showed a relative small tunability value of the film with BMN/Pt interface structure. It suggests that the interface state between the films and substrates, electric field distribution, and orientation degree are responsible for the impacts on the microstructure and tunable dielectric properties of the BMN thin films.     

Structural and electrical properties of Na0.5Bi4.0RE0.5Ti4O15 (RE=Tm,Yb and Lu) thin films

In the current study, a series of lanthanide ions, Tm, Yb and Lu, were used for doping at the Bi-site of the Aurivillius phase Na_0.5Bi_4.5Ti₄O₁₅ (NaBTi) to investigate the structural, electrical and ferroelectric properties of the thin films. In this regard, Na_0.5Bi_4.5Ti₄O₁₅ and the rare earth metal ion-doped Na_0.5Bi_4.0RE_0.5i₄O₁₅ (RE=Tm, Yb and Lu, denoted by NaBTmTi, NaBYbTi, and NaBLuTi, respectively) thin films were deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method. Formations of the Aurivillius phase orthorhombic structures for all the thin films were confirmed by X-ray diffraction and Raman spectroscopic studies. Based on the experimental results, the rare earth metal ion-doped Na_0.5Bi_4.0RE_0.5Ti₄O₁₅ thin films exhibited a low leakage current and the improved ferroelectric properties. Among the thin films, the NaBLuTi thin film exhibited a low leakage current density of 6.96×10⁻⁷ A/cm² at an applied electric field of 100 kV/cm and a large remnant polarization (2P_r) of 26.7 μC/cm² at an applied electric field of 475 kV/cm.     

Effects of the sulfurization temperature on sol gel-processed Cu2ZnSnS4 thin films

As a promising and alternative solar absorber material, the copper–zinc–tin–sulfide compound (Cu₂ZnSnS₄) has been drawing attention in recent years for the production of cheap thin-film solar cells owing to the high natural abundance and non-toxicity of all the constituents, a tunable direct-band-gap energy and a large optical absorption coefficient. In addition, to overcome the problem of expensive vacuum-based methods, solution-based approaches are being developed for Cu₂ZnSnS₄ deposition. In this study, we have produced Cu₂ZnSnS₄ thin films via the sol–gel technique and subsequent sulfurization. The effects of the sulfurization temperature on the structural, morphological, compositional and optical properties of the films were investigated. X-ray diffraction and Raman spectroscopy analyses confirmed the formation of phase-pure CZTS films. The crystallinity of the films increased with an increasing sulfurization temperature. From the surface images and the results of the composition analysis, it was found that the films are uniform, composed of homogenously distributed grains and have compositions with Cu deficit. The values of the optical absorption coefficients for the films were found to be 10⁴ cm^?1 based on absorbance spectroscopy. The optical band-gap values were estimated to be between 1.32 and 2.27 eV depending on the sulfurization temperature.     

Enhanced dielectric tunability properties of Ba(ZrxTi1−x)O3 thin films using seed layers on Pt/Ti/SiO2/Si substrates

The compositionally graded and homogeneous Ba(Zr_xTi_1−x)O₃ (BZT) thin films were fabricated on LaNiO₃ (LNO) buffered Pt/Ti/SiO₂/Si and Pt/Ti/SiO₂/Si substrates by a sol–gel deposition method, respectively. These films crystallized into a single perovskite phase. The BZT thin films deposited on LaNiO₃/Pt/Ti/SiO₂/Si substrates had a highly (1 0 0) preferred orientation and exhibited a preferred (1 1 0) orientation when the thin films were deposited on Pt/Ti/SiO₂/Si substrates. The LNO and Ba(Zr_0.30Ti_0.70) served as seed layer on Pt/Ti/SiO₂/Si substrates and analyze the relationship of seed layer, microstructure and dielectric behavior of the thin films. The compositionally graded thin films from BaTiO₃ to BaZr_0.35Ti_0.65O₃ were fabricated on LNO/Pt/Ti/SiO₂/Si substrates. The tunability behavior of compositionally graded films was analyzed in order to produce optimum effective dielectric properties. The dielectric constant of BaZr_xTi_1−xO₃ compositionally graded thin films showed weak temperature dependence. This kind of thin films has a potential in a fabrication of a temperature stable tunable device.     

Ca掺杂对Ba0.8Sr0．2TiO3本征热释电性能的影响

以尿素（Urea）为添加剂,用溶胶一凝胶工艺在较低温（550℃）合成了钛酸锶钡粉末,在1300℃烧结成陶瓷。研究了Ca掺杂量对陶瓷结构、介电、铁电以及本征热释电性能的影响。研究显示：陶瓷样品均形成了单一的钙钛矿结构固溶体。陶瓷的本征热释电性能受Ca掺杂量影响显著。当Ca掺杂量为2at％时,陶瓷在居里点附近的本征热释电系数达670nC·cm^-1·k^-1。     

La0.8Sr0.2MnO3涂覆液浓度对La0.8Sr0.2FeO3电极电化学性能的影响

研究了0.005、0.010、0.020、0.035和0.040 mol/L5种不同浓度的La0.8Sr0.2MnO3 (LSM)溶液涂覆La0.8Sr0.2FeO3 (LSF)电极后,其电化学性能的变化.X射线衍射结果表明:LSM和LSF化学相容性好.扫描电子显微镜观察可见:电极的晶粒尺寸和涂层厚度随着涂覆液浓度的增加而增加.电化学阻抗谱表明:在阳极极化条件下,经过0.010 mol/L LSM溶液涂覆处理后的LSF电极表现为最佳的电化学性能,其极化电阻在800℃仅为0.3Ω·cm2.而且无论在阳极极化还是阴极极化处理后,涂覆LSM后的LSF电极的极化电阻,1200 s内都呈现下降的趋势,LSM涂覆后的LSF电极具有一定的抗阳极极化的能力,归因于LSM涂层的良好催化特性.因此,0.010 mol/L LSM溶液涂覆处理后的LSF可以作为固体氧化物电解池的阳极材料.     

Synthesis and photoluminescence properties of CaGd2(MoO4)4:Eu3+ red phosphors

The novel red-emitting Eu³⁺ ions activated CaGd₂(MoO₄)₄ phosphors were prepared by a citrate sol–gel method. The X-ray diffraction patterns confirmed their tetragonal structure when the samples were annealed above 600 °C. The photoluminescence excitation spectra of CaGd₂(MoO₄)₄:Eu³⁺ phosphors exhibited the charge transfer band (CTB) and intense f–f transitions of Eu³⁺ ion. The optimized annealing temperature and Eu³⁺ ion concentration were analyzed for CaGd₂(MoO₄)₄:Eu³⁺ phosphors based on the dominant red (⁵D₀→⁷F₂) emission intensity under NUV (394 nm) excitation. All decay curves were well fitted by the single exponential function. These luminescent powders are expected to find potential applications such as WLEDs and optical display systems.     

A novel low cost method for the synthesis of ceramic nano silicon oxycarbide powder

Although different methods have been used for manufacturing micro- Silicon Oxycarbide (SiOC) powder, there is no account of nano-SiOC synthesis in the literature. In this study, a novel low cost sol–gel method was used for the synthesis of nano-silicon oxycarbide (SiOC) powder. An organic–inorganic hybrid, i.e., a Tetraethyl Ortosilicate/Polydimethylsiloxane (TEOS/PDMS) mixture, was used as the starting material. The sol–gel technique was employed to cross-link the precursors using a base catalyst. Consequently, the gel was dried at 90 °C for 24 h. The dried gel was pyrolyzed in a two-step process in argon atmosphere. The synthesized powder was investigated using XRD, FTIR, TGA, FESEM and BET techniques. XRD and FTIR analyses identified the product to be SiOC. BET analysis showed a specific surface area of about 150 m²/g for the synthesized powder, thereby suggesting its nano-sized characteristics. FESEM studies further confirmed that the powder was nano-sized with an average particle size of about 50 nm. The proposed procedure could be, therefore, a simple low cost method for the synthesis of nano-SiOC powder.     

Photoluminescence and electron-beam excitation induced cathodoluminescence properties of novel green-emitting Ba4La6O(SiO4)6:Tb3+phosphors

Tb³⁺ions activated Ba₄La₆O(SiO₄)₆ (BLSO:Tb³⁺) phosphors were synthesized by a citrate sol-gel method. The X-ray diffraction pattern confirmed their oxyapatite structure. The field-emission scanning electron microscope image established that the BLSO:Tb³⁺phosphor particles were closely-packed and acquired irregular shapes. The photoluminescence (PL) excitation spectra of BLSO:Tb³⁺phosphors showed intense f–d transitions along with low intense peaks corresponding to the f–f transitions of Tb³⁺ions in the lower energy region. The PL emission spectra displayed the characteristic emission bands of Tb³⁺ions, and the optimized concentrations were found to be at 1 and 6 mol% for blue and green emission peaks, respectively. The cathodoluminescece (CL) spectra exhibited a similar behavior that was observed in the PL spectra except the intensity variations in the blue and green regions. The CL spectra of the BLSO:6 mol% Tb³⁺phosphor unveiled accelerating voltage induced luminescent properties.     

Processing and dielectric characterization of Ba0.3Sr0.7TiO3 thin films on alumina substrates

Ba_0.3Sr_0.7TiO₃ (BST) thin films were prepared from the sols based on alkaline earth acetates and titanium propoxide in 2-methoxyethanol–acetic acid solvents and deposited on polished alumina substrates by spin coating. The perovskite phase crystallizes upon heating at/above 700 °C. By increasing the annealing temperature from 700 to 900 °C the grain size increases from 40 to 80 nm, due to the increased driving force for crystallization. The annealing time has got only a minor influence on grain size as a consequence of constrained conditions of the film. The dielectric permittivity and tunability (ɛ_0 V/ɛ_200 V) of BST films, measured at 1 MHz, strongly depend on the grain size, exhibiting the values of 345 and 1.47, and 722 and 1.93 for the films with 40 and 80 nm-sized grains, respectively.     

Effect of heat treating gel films on the formation of superhydrophobic boehmite flaky structures on austenitic stainless steel

The effect of heat treating gel films at different temperatures on the formation of the boehmite flaky structures on AISI 316 type austenitic stainless steel is investigated. After heating at different temperatures, the reactivity of the gel films with boiling water to form boehmite flakes was different, which resulted in different morphologies and different contact angle values after coating with hydrolyzed (heptadecafluoro-1,1,2,2-tetrahydrodecyl)trimethoxysilane (FAS). When the gel film was heat treated from 200 to 600 °C, the resulting contact angle was above 150°, indicating superhydrophobic behavior. However, when the gel film was heat treated below 200 °C as well as at 700 and 800 °C, only some boehmite flakes were formed; when the gel film was heat treated at 900 °C, no boehmite flakes were observed. In these cases the surface roughness is insufficient for the superhydrophobicity. The formation condition of the boehmite flakes by reaction of the gel film with boiling water is also tentatively discussed.     

Effects of deposition temperature on the crystallinity of Ba0.5Sr0.5TiO3 epitaxial thin films integrated on Si substrates by pulsed laser deposition method

Epitaxial Ba_0.5Sr_0.5TiO₃ (BSTO) thin films were grown on TiN buffered Si (0 0 1) substrates by PLD method and the effects of deposition temperature on their crystallinity and microstructure were studied. BSTO thin films were prepared with substrate temperature ranging from 350 to 650 °C. The BSTO films grown at below 400 °C showed amorphous phase and the film grown at 450 °C showed mixed phase of crystalline and amorphous, where crystalline phase was observed only at the top surface portion of the film. The BSTO films with fully crystalline phase were obtained in the samples deposited at above 500 °C. The (0 0 l) preferred orientation and the crystallinity of the BSTO films were improved with increasing the temperature. The dielectric constant, measured at 100 kHz and at room temperature, of the BSTO film grown at 650 °C was measured to be as high as 1129.     

CO2 laser-assisted preparation of transparent Eu2Ti2O7 thin films

We present a laser-assisted preparation of transparent europium-titanate Eu₂Ti₂O₇ thin films with tailored structural and optical properties. We have evaluated the effects of the irradiation time on the structural and the optical properties of the films. This approach allows the preparation of nanocrystalline crack-free films and micro patterns. The amorphous thin films were prepared by a sol-gel method. The films were annealed by a CO₂ laser beam for various time intervals. The laser irradiation induced a crystallization process that resulted in the formation of Eu₂Ti₂O₇ nanocrystals. The nanocrystals regularly grew with increasing irradiation time reaching the size from 25?nm to 45?nm. A film of a thickness 480?nm exhibited an optical transmission of 91.9% that is close to the maximal theoretical limit. The film's refractive index at 632?nm was 2.26. A micrometric pattern was prepared by a direct laser writing followed by a wet chemical etching. Feasibility of the demonstrated approach, together with the high film's quality, and europium-titanate chemical resistivity open up many opportunities for advanced applications. The approach can be used for a preparation of protective coatings and integrated photonic devices such as planar optical waveguides and couplers.     

Tunable performance of BaZr0.2Ti0.8O3 thin films prepared by pulsed laser deposition

BaZr_0.2Ti_0.8O₃ (BZT) thin films were deposited at various oxygen pressures (0–60 Pa) on Pt/TiO_x/SiO₂/Si substrates by using pulsed laser deposition. The crystallinity of the thin films initially improves but subsequently deteriorates with increasing oxygen pressure. The tunable performance of BZT thin films is associated with crystal structure and oxygen vacancies. The theoretical mechanisms for the relative permittivity and dielectric loss as a function of electric field are proposed. The frequency response of dielectric properties is also investigated and the variation mechanisms are supposed. Eventually, BZT thin films fabricated under 15 Pa have the highest tunability (70.3% at 400 kV/cm) with the largest relative permittivity of 486, the lowest loss tangent of 0.021 and the maximum commutation quality factor of 7744.8. The results imply that BZT thin films are potential candidates for tunable device applications.     

Crystal structure refinement,enhanced magnetic and dielectric properties of Na0.5Bi0.5TiO3 modified Bi0.8Ba0.2FeO3 ceramics

(1-x) Na_0.5Bi_0.5TiO₃–x(Bi_0.8Ba_0.2FeO₃) (x=0.5, 0.6, 0.7, and 0.8) ceramics were synthesized via solid state reaction method. Powder X-ray diffraction investigations performed at room temperature along with Rietveld analysis show all the composites to exhibit a rhombohedral distorted perovskite structure, described by space group R3c. Rietveld refinement confirmed a good agreement between observed and calculated intensities and a low value of goodness of fit (χ²). Magnetic measurements were carried out at room temperature up to a field of 6 kOe. Magnetic properties of BBFO modified NBT ceramics are improved with a significant opening in the M–H hysteresis loop at room temperature. Remanent magnetization and coercive field increased with increase of BBFO concentration. The dielectric response of these samples was analyzed in the frequency range 10 Hz–7 MHz at different temperatures revealing a dispersion in dielectric constant (ε′) and in dissipation factor (tan δ) at lower frequencies. Both ε′ and tan δ increase with increase of BBFO content. The temperature dependence of frequency exponent ′s′ of power law suggests that quantum mechanical tunneling (QMT) model to be applicable at lower temperature and correlated barrier hopping (CBH) mechanism to be appropriate at higher temperature to describe the conduction mechanism in x=0.5 and x=0.6 samples. Further, with increase in BBFO content, the dielectric constant becomes more stable at higher frequencies and temperatures thereby improving the dielectric properties of the material.     

Enhanced dielectric loss of Mg doped Ba0.7Sr0.3TiO3 ceramics

The effect of MgO doping on the structural, microstructural and dielectric properties of Ba_0.7Sr_0.3TiO₃ (BST) ceramic from the point of view of its application in microwave tunable devices has been studied. All the samples crystallize into perovskite structure. There is significant reduction in the value of loss factor with the increase in Mg-level, the dielectric constant and tunability are also reduced with the increase in Mg-level. Interestingly, the Fig. of merit of the material is found to be enhanced with increase of Mg-doping. The observed dielectric properties are explained on the basis of defect chemistry involved when Mg is doped in Ba_0.7Sr_0.3TiO₃ ceramics. The effect of dc field on the dielectric constant and the dielectric breakdown strength of the paraelectric phase Mg doped BST ceramic samples are also studied.