Structural,magnetic and electronic structure properties of pure and Ti doped Mg0.95Mn0.05Fe2O4 nanocrystalline thin films

Thin films of pure and Ti doped Mg_0.95Mn_0.05Fe₂O₄ deposited using pulsed laser deposition technique, have been characterized using X-ray diffraction, Raman spectroscopy, dc magnetization, atomic force microscopy, magnetic force microscopy and near edge X-ray absorption fine structure spectroscopy measurements. X-ray diffraction and Raman spectroscopy measurements indicate that both the films have single phase and the polycrystalline behavior with FCC structure. The grain size calculated using XRD data was 18 and 27 nm for pure and Ti doped films, respectively. Magnetic measurements reflect that pure film has superparamagnetic behavior while Ti doped film has soft ferrimagnetic behavior at room temperature. Atomic force microscopy measurements indicate that both the films are nanocrystalline in nature. Near edge X-ray absorption fine structure spectroscopy measurements clearly infer that Fe ions are in mixed valence state.     

水热合成Zn0.95Ni0.05O稀磁半导体纳米晶

采用水热法,分别以2 mol/L的NaOH和KOH作为矿化剂,在240℃保温24h,合成了Zn0.95Ni0.05O稀磁半导体纳米晶粉体.X射线衍射结果表明:Ni离子取代Zn离子,并且没有出现杂质相.紫外-可见光吸收光谱测试进一步表明,Ni离子已进入ZnO晶格内;采用能谱测试表明,Ni离子的实际掺杂摩尔分数为3.20%.室温下,通过振动样品磁强计测试表明,所制备的Zn0.95Ni0.05O纳米晶体具有优良的铁磁性能.     

Effects of LiF addition on sintering behavior and microwave dielectric properties of (Mg0.95Zn0.05)2(Ti0.8Sn0.2)O4 ceramics

The effects of LiF addition on the sinterability and microwave dielectric properties of (Mg_0.95Zn_0.05)₂(Ti_0.8Sn_0.2)O₄ (MZTS) ceramics were investigated. A small amount of LiF addition can effectively lower the sintering temperature of MZTS from 1325 °C to 1150 °C due to the liquid phase effect and induce no apparent degradation of the microwave dielectric properties. With increasing LiF content, the apparent density and dielectric constant decreased gradually, the quality factor increased firstly and then decreased. In particular, MZTS–3.0 wt% LiF ceramics sintered at 1150 °C for 5 h exhibited good microwave dielectric properties of ?_r = 13.05, Q · f = 119,310 GHz (at 10 GHz) and τ_f = ?59.2 ppm/°C.     

Synthesis, structure and magnetic properties of β-MnO 2 nanorods

We present synthesis, structure and magnetic properties of structurally well-ordered single-crystalline β-MnO₂ nanorods of 50–100 nm diameter and several μm length. Thorough structural characterization shows that the basic β-MnO₂ material is covered by a thin surface layer (∼2.5 nm) of α-Mn₂O₃ phase with a reduced Mn valence that adds its own magnetic signal to the total magnetization of the β-MnO₂ nanorods. The relatively complicated temperature-dependent magnetism of the nanorods can be explained in terms of a superposition of bulk magnetic properties of spatially segregated β-MnO₂ and α-Mn₂O₃ constituent phases and the soft ferromagnetism of the thin interface layer between these two phases.     

Oxygen Nonstoichiometry and Thermodynamic Quantities of La2Ni0.95Al0.05O4.025 + δ

The oxygen nonstoichiometry of La₂Ni_0.95Al_0.05O_4.025 + δ (LNAO) is measured as a function of oxygen partial pressure (pO₂) and temperature by coulometric titration method and thermogravimetric analysis (TGA) in 800°C–1000°C temperature range and 10^?16‐1 atm pO₂ range. The partial molar quantities for mixing of oxygen were calculated and results were compared with the literature results on La₂NiO_4 + δ (LNO). The variation in activity coefficient of holes versus oxygen nonstoichiometry illustrated an early positive deviation of the activity coefficient of holes from unity, leading to  ≈  7 at δ  ≈  0.08, which was lower than the literature value of  ≈  14 for La₂NiO_{4  +  δ} at δ  ≈  0.08, indicating lesser deviation of LNAO from ideal solution behavior. The effective mass of holes () was 1.02–1.21 times the rest mass (m_o), which indicated the band‐like conduction and allowed the effect of the small degree of polaron hopping to be ignored. The comparison of oxygen nonstoichiometry and partial molar quantities showed that incorporation of interstitial oxygen is less favorable in LNAO in comparison to LNO.     

Structural,electronic paramagnetic resonance and magnetic properties of praseodymium-doped rare earth CeO2 semiconductors

In this work, praseodymium (Pr) doped cerium oxide (CeO₂) was prepared using the microwave-assisted hydrothermal method (MAH) and the properties were investigated by X-ray diffraction analysis (XRD), Raman spectroscopy, Field Emission Gun Scanning Electron Microscope (FEG-SEM), BET method, Photoluminescence spectroscopy (PL), Fourier-transform infrared spectroscopy (FTIR), Ultraviolet–visible spectroscopy (UV–Vis), Electron paramagnetic resonance spectroscopy (EPR) and Magnetometry. The results showed that increasing the Pr-doping promotes a structural disorder due to increased oxygen vacancies. XRD confirmed a cubic structure without deleterious phases with modifications in the structure caused by alteration in the cerium oxidation state as well as changes in the crystallite size and strain obtained by Wellinson-Hall method. Raman spectroscopy shows that changing the Pr content results in samples with different defect densities at short range. FEG-SEM showed that the nanocrystals are agglomerated with small particles tend to aggregate spontaneously to decrease the surface energy. BET method showed that the Pr doping results in a gain of specific surface area. PL indicated that Pr³⁺ leads to distinct emissions; red emission associated to oxygen vacancies located near the conduction band (shallow defects), green emission associated to electron-hole recombination and orange emission associated to shallow defects and electron-hole recombination. FTIR indicated the complete process of nucleation with no other phase. UV–Vis showed the transitions between oxygen 2p, cerium 4f and praseodymium 4f states. The EPR signal shows events occurring around 344 mT. These events can be related due the presence of paramagnetic elements containing unpaired electrons, such as Ce (III), which is indicative of cerium reduction caused by Pr ions, as evidenced by Rietveld data. Regardless of the Pr concentration used in this research, the magnetic measurements show a superparamagnetic system below the blocking temperature of ~20 K and a paramagnetic system above this temperature, which indicates no significant changes in the average size of the nanoparticles. Surface area, crystallite size and the temperature are important parameters, which control the magnetic properties of such N-type semiconductors.     

Dielectric properties of (Ba0.95Ca0.05)(Ti1-yCay)O3-y ceramics

Calcium doped barium titanate ceramics with composition (Ba_0.95Ca_{0. 05}) (Ti_1-yCa_y)O_3-y prepared by a liquid mixing technique were used to measure the dielectric properties. The pure barium titanate and lightly-Ca-doped materials obey a Curie Weiss law when the temperature is above the Curie temperature. It has been found that the average cubic-tetragonal phase transition temperature moves downward when the octahedrally-coordinated Ca concentration increases, and heavily-Ca-doped barium titanate ceramics show relaxor behavior with a diffuse phase transition characteristic (DPT). Above the average transition temperature T_av the dielectric properties for heavily doped materials do not obey the Curie Weiss law, but can be described by a quadratic relation over a wide range of temperature. Experiments have shown that there exists an extra K(T) peak attributable to the existence of separate microregions of Ba_0.95Ca_0.05TiO₃ in a matrix of (Ba_0.95Ca_0.05) (Ti_1-yCa_y)O_3-y (where y ≤ 2%).     

Structural,Optical, and Piezoelectric Response of Lead‐Free Ba0.95Mg0.05Zr0.1Ti0.9O3 Nanocrystalline Powder

Nanocrystalline powders of Ba_1?xMg_xZr_0.1Ti_0.9O₃ (x = 0.025–0.1) were synthesized via citrate assisted sol–gel method. Interestingly, the one with x = 0.05 in the system Ba_1?xMg_xZr_0.1Ti_0.9O₃ exhibited fairly good piezoelectric response aside from the other physical properties. The phase and structural confirmation of synthesized powder was established by X‐ray powder diffraction (XRD) and Raman Spectroscopic techniques. Two distinct Raman bands i.e., 303 and 723 cm^?1 characteristic of tetragonal phase were observed. Thermogravimetric analysis (TGA) was performed to evaluate the phase decomposition of the as‐synthesized Ba_0.95Mg_0.05Zr_0.1Ti_0.9O₃ sample as a function of temperature. The average crystallite size associated with Ba_0.95Mg_0.05Zr_0.1Ti_0.9O₃ was calculated using Scherrer formula based on the XRD data and was found to be 25 nm. However, Scanning and Transmission Electron Microscopy studies revealed the average crystallite size to be in the range of 30–40 nm, respectively. Kubelka–Munk function was employed to determine the optical band gap of these nanocrystallites. A piezoelectric response of 26 pm/V was observed for Ba_0.95Mg_0.05Zr_0.1Ti_0.9O₃ nanocrystal by Piezoresponse Force Microscopy (PFM) technique. Photoluminescence (PL) study carried out on these nanocrystals exhibited a blue emission (470 nm) at room temperature.     

Influence of cobalt and sintering temperature on structure and electrical properties of BaZr0.05Ti0.95O3 ceramics

Pure and Co-modified BaZr_0.05Ti_0.95O₃ ceramics were fabricated by the traditional solid state reaction technique. The influence of cobalt and sintering temperature on structure, dielectric, ferroelectric properties and diffuse phase transition of BZT ceramics were investigated systematically. 1300 °C was the optimal sintering temperature for BZT ceramics. The solid solubility limit of Co ions in BZT matrix was determined to be 0.4 mol%. The introduction of a moderate amount of Co ions was believed to benefit the microstructure development and make the grain size more uniform. Compared with undoped counterparts, 0.4 mol% Co-modified ceramics showed equivalent ferroelectric properties with a high remnant polarization (P_r=9.6 μC/cm²) and a low coercive field (E_c=0.21 kV/mm). Besides these, a relative high dielectric coefficient (ε_r=2030) and a low dielectric loss (tan δ=1.85%) were also obtained on this composition. The degree of diffuse phase transition was enhanced by the addition of Co ions. The related mechanism of the diffused phase transition behavior was discussed.     

Zn0.95Fe0.05O稀磁半导体粉体的制备与表征

采用水热法合成Zn_(0.95)Fe_(0.05)O稀磁半导体,通过试验及XRD、FE-SEM对合成的粉体进行分析,在水热合成法合成条件200℃保温24 h、矿化剂NaOH浓度3 mol/l、填充度为60%下,制备出的Zn_(0.95)Fe_(0.05)O纳米晶体发育完全,粒度分布均匀。是合成Zn_(0.95)Fe_(0.05)O纳米晶体的理想方法之一。     

A facile surfactant-free method to prepare Ti0.95Er0.05O2 nanocrystal and its photocatalytic performance

The preparation of Ti_0.95Er_0.05O₂ nanocrystal by a facile surfactant-free hydrothermal method was reported in this work. The obtained materials were investigated by means of HRTEM, SEM, EDS, XPS and XRD. The results indicated that Ti_1 − xEr_xO₂ were obtained in uniform nanometer scale and very pure. According to the photocatalytic activity for the photocatalytic degradation of methylene blue, Ti_0.95Er_0.05O₂ is nearly twice higher than that of the undoped sample. Furthermore, photoelectrochemical investigation has been carried out. The photocurrent intensity of Ti_0.95Er_0.05O₂ is nearly twice higher than that of the undoped TiO₂, which is in well accordance with their photocatalytic performance.     

Microwave dielectric properties and microstructures of Nb2O5-Zn0.95Mg0.05TiO3 + 0.25TiO2 ceramics with Bi2O3 addition

The effects of Bi₂O₃ addition on the microwave dielectric properties and the microstructures of Nb₂O₅-Zn_0.95Mg_0.05TiO₃ + 0.25TiO₂ (Nb-ZMT′) ceramics prepared by conventional solid-state routes have been investigated. The results of X-ray diffraction (XRD) indicate the presence of four crystalline phases, ZnTiO₃, TiO₂, Bi₂Ti₂O₇, and (Bi_1.5Zn_0.5)(Ti_1.5Nb_0.5)O₇ in the sintered ceramics, depending upon the amount of Bi₂O₃ addition. In addition, in order to confirm the existence of (Bi_1.5Zn_0.5)(Ti_1.5Nb_0.5)O₇ phase in the samples, the microstructure of Nb-ZMT′ ceramic with 5 wt.% B₂O₃ addition was analyzed by using a transmission electron micrograph. The dielectric constant of Nb-ZMT′ samples was higher than ZMT′ ceramics. The Nb-ZMT′ ceramic with 5 wt.% Bi₂O₃ addition exhibits the optimum dielectric properties: Q × f = 12,000 GHz, ?_r = 30, and τ_f = ?12 ppm/°C. Unlike the ZMT′ ceramic sintered at 900 °C, the Nb-ZMT′ ceramics show higher Q value and dielectric constant. Moreover, there is no Zn₂TiO₄ existence at 960 °C sintering. To understand the co-sinterability between silver electrodes and the Nb-ZMT′ dielectrics, the multilayer samples are prepared by multilayer thick film processing. The co-sinterability (900 °C) between silver electrode and Nb-ZMT′ dielectric are well compatible, because there are no cracks, delaminations, and deformations in multilayer specimens.     

Preparation,Characterization, and Thermophysical Properties of (La0.95Sr0.05)2Ce2O6.95 Ceramic for Thermal Barrier Coatings

The La₂Ce₂O₇ powder doped with Sr was synthesized by sol‐gel method in this study and its dense bulk samples were also prepared by pressureless‐sintered at 1600°C for 10 h. Its phase composition, microstructure, and thermophysical property were investigated. Results reveal that pure (La_0.95Sr_0.05)₂Ce₂O_6.95 with single fluorite structure was successfully synthesized. Microstructure of bulk sample is dense. Its thermal expansion coefficient is higher than that of Y₂O₃‐stabilized ZrO₂ (YSZ) and its thermal conductivity is lower than that of YSZ. These results show that (La_0.95Sr_0.05)₂Ce₂O_6.95 ceramic can be explored as the candidate material for thermal barrier coatings.     

Structural,spectral, dielectric and magnetic properties of Ni0.5MgxZn0.5-xFe2O4 nanosized ferrites for microwave absorption and high frequency applications

Ni_0.5Mg_xZn_0.5−xFe₂O₄ (x=0, 0.1, 0.2, 0.3, 0.4 and 0.5) (NiMgZn) nano-sized ferrites were synthesized via sol-gel route. The average cation radius, bond lengths (A and B sites), shared (d_AE, d_BE) and unshared edges (d_BEU) of the NiMgZn nanoferrites were determined from the XRD data. FTIR studies confirmed the spinel structure of NiMgZn nanoferrites. The force constant at tetrahedral and octahedral sites were calculated. The surface morphology was investigated from the micrographs. The dielectric parameters such as dielectric constant, dielectric loss factor, loss tangent and Q values with different concentration of Mg in NiZn nanoferrite were evaluated. It was found that the NiMgZn sample at x=0.5 showed high Q values with low dielectric losses at higher frequencies. The squareness ratio and coercivity values confirmed the super paramagnetic behaviour of the NiMgZn nano-sized ferrites. However, the saturation and remanence increased with the increasing Mg contents whereas coercivity values follow the Stoner-Wolforth model for NiMgZn at x=0, 0.2, 0.3 and 0.4. The NiMgZn nano-sized ferrites samples at x=0.1 and 0.5 show the variations in coercivity values which may be due to the strong LS coupling and super-exchange interactions of the metal cations at tetrahedral and octahedral sites. The dielectric and magnetic studies of NiMgZn nano-sized ferritesexplored their application in various technological and industrial fields such as magnetic storage, microwave absorption and high frequency applications.     

Nucleation sequence on the cation exchange process between Y0.95Eu0.05PO4 and CePO4 nanorods

Nanorods of Y0.95Eu0.05PO4@CePO4 (Y0.95Eu0.05PO4 phase was nucleated first and then a CePO4 phase was nucleated) and CePO4@Y0.95Eu0.05PO4 (CePO4 phase was nucleated first and then Y0.95Eu0.05PO4 phase was nucleated) were prepared at a relatively low temperature of 140 °C in ethylene glycol medium. Based on XRD, TEM and Raman studies it has been inferred that Y0.95Eu0.05PO4@CePO4 sample consists of a mixture of bigger (length around 800-1000 nm and width around of 80-100 nm) and smaller (length around 70-100 nm and width around 10-20 nm) nanorods, having monoclinic CePO4 and tetragonal YPO4 structure, whereas CePO4@Y0.95Eu0.05PO4 sample consists of mainly small nanorods having a single phase CePO4 structure. From the detailed luminescence studies it has been established that there exists significant incorporation of Y3+/Eu3+ ions in the CePO4 phase in CePO4@Y0.95Eu0.5PO4 sample. This has been attributed to the cation exchange taking place between Ce3+ ions in CePO4 host and Eu3+ and Y3+ ions in solution during the synthesis stage. Unlike this, such an exchange is not possible for Y0.95Eu0.05PO4@CePO4 sample synthesized under identical conditions due to the higher solubility product (Ksp) value of YPO4 compared to CePO4. Incorporation of Eu3+ in the CePO4 lattice of CePO4@Y0.95Eu0.5PO4 sample is confirmed by the significant reduction in the lifetime of 5D0 level of Eu3+ and the luminescence intensity from Eu3+, arising due to the electron transfer between the Ce3+/Ce4+ and Eu3+/Eu2+ species. These results are further supported by the non-radiative decay rates and quantum yields calculated from the emission spectrum.     

Enhanced pyroelectric figure of merits of porous BaSn0.05Ti0.95O3 ceramics

Porous BaSn_0.05Ti_0.95O₃ (BTS) ceramics were prepared by sintering compacts consisting of BTS and Poly (methyl methacrylate)(PMMA)as pore former. Porous BTS ceramics were systematically characterized for microstructural, ferroelectric, dielectric and pyroelectric properties. Porosity increased from 4% to 22.5% with increasing PMMA content. Dielectric constant decreases and loss increases with porosity. At 22.5% porosity, relative dielectric constant of BTS decreased by 47% (from 2525 to 1335) at 1 MHz/303K. Porosity leads to significant reduction in dielectric constant and volume specific heat capacity, which are of great interest for improving pyroelectric figure of merits (FOMs). Further, FOMs for current responsivity (F_i), voltage responsivity (F_v), detectivity (F_d) and energy harvesting (F_e and F_e^*) are calculated. Compared with dense ceramic, 2% PMMA specimen showed an improvement of F_e by 166% and F_e^*by 177%. F_v increased by 77%, F_d by 73% and F_i by 56% at 303K. All of these advancements are favorable for pyroelectric device applications.     

Magnetic and electrical properties of La0.7Ca0.3Mn0.95Co0.05O3 epitaxial layers by pulsed laser deposition

Epitaxial La_0.7Ca_0.3Mn_0.95Co_0.05O₃ (LCMCO) thin films were prepared on (1 0 0) LaAlO₃ single-crystal substrates by pulsed laser deposition (PLD). We have been studied using X-ray diffraction (XRD), electrical transport magneto-transport and dc magnetization. XRD pattern reflects that all films have c-axis epitaxial growth on LaAlO₃ substrates. The decrease in out-of-plane cell parameter specifies a progressive relaxation of in the plane compressive strain as the thickness film is increases. From the dc magnetization measurements, it is observed that ferromagnetic to paramagnetic transition temperature increases with increase in the film thickness. Magneto-resistance and temperature coefficient of resistance increases with thickness of film and have maximum value near its metal to insulator transition temperature.     

(Sn1-x,Ni2x)O2纳米颗粒膜的制备及半导体性能

为提高SnO2的半导体性能,以分析纯SnCl2.2H2O和NiCl2.6H2O为主要原料,控制不同n(Ni2+)/n(Sn2+),利用溶胶凝胶-浸渍提拉法制备了(Sn1-x,Ni2x)O2纳米颗粒膜及半导体元件。用XRD、AFM对样品的结构、形貌进行了分析,并测试了(Sn1-x,Ni2x)O2元件的半导体性能。结果表明,(Sn1-x,Ni2x)O2纳米颗粒膜表面椭球形颗粒排列致密,尺寸约30 nm,(Sn1-x,Ni2x)O2为金红石型结构,但Ni2+代替了SnO2晶格中的部分Sn4+,使其晶胞参数a轴长平均减小0.000 4 nm,c轴长平均减小0.000 3 nm;随n(Ni2+)/n(Sn2+)由0.006增大到0.03,(Sn1-x,Ni2x)O2的晶粒尺寸由约45 nm减小至约18 nm;随温度由30℃上升至150℃,n型(Sn1-x,Ni2x)O2半导体元件的电阻约减小至其10%,而纯净SnO2元件的电阻仅约减小至其15%;随n(Ni2+)/n(Sn2+)的增大,离子化杂质散射增强,(Sn1-x,Ni2x)O2内部载流子迁移率下降,元件在150℃左右的电阻也由4.8 kΩ增大至12.1 MΩ,提高了元件的半导体性能。     

Enhanced Room Temperature Multiferroic Properties of (Bi0.95La0.05)(Fe0.97Mn0.03)O3/CoFe2O4 and CoFe2O4/(Bi0.95La0.05)(Fe0.97Mn0.03)O3 Double‐Layered Thin Films

Multiferroic (Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/CoFe₂O₄ and CoFe₂O₄/(Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃ double‐layered thin films were prepared on Pt(111)/Ti/SiO₂/Si(100) substrates via a chemical solution deposition method. In both the thin films, superior multiferroic properties were observed at room temperature. However, substantial enhancements in magnetic properties, such as saturated ferromagnetic hysteresis loop with large 2M_r (68.8 emu/cm³) and 2H_c (11.7 kOe), as well as moderate ferroelectric properties, such as 2P_r (58 μC/cm²) with low leakage current density (4 × 10^?9 A/cm² at 100 kV/cm), were observed in the (Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/CoFe₂O₄ at room temperature. Structural distortion, deformation of [(Fe, Mn)O₆] oxygen octahedra, and superexchange interaction in the (Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃ are attributed to the enhanced properties.     

Mechanism of anti-stokes photoluminescence in Ag0.05Ga0.05Ge0.95S2-Er2S3 glassy alloys

The absorption and up-conversion photoluminescence spectra of alloys of the Ag_0.05Ga_0.05Ge_0.95S_2?x Er₂S₃ system (100 ? x), excited with 980-nm laser irradiation, where x = 0.42, 0.25, and 0.18 mol %, have been studied. Green, intensive red, and infrared luminescence, which is caused by electronic ² H _11/2 → ⁴ I _15/2, ⁴ F _9/2 → ⁴ I _15/2, ⁴ S _3/3 → ⁴ I _13/2 transitions in Er³⁺ ions, respectively, and connected with two photon up-conversion processes was recorded in all samples. The changes in the intensities of glassy alloys of radiation bands with different erbium contents and the influence of large structure defects on the processes of the occupation and the devastation of the energetic levels of erbium ions.