Grain growth in Mn-doped ZnO

Grain growth in ZnO doped with 0.1 to 1.2 mol% Mn was investigated during isothermal sintering from 1100 to 1300°C in air. Mn doping promotes the grain growth of ZnO during sintering, and this effect is enhanced by increasing the Mn doping level. The grain growth exponent is reduced from 3.4, for undoped ZnO, to 2.4, for ZnO doped with 1.2 mol% Mn, while the apparent activation energy for grain growth is reduced from 200 kJ/mol, for undoped ZnO, to 100–150 kJ/mol, for Mn-doped ZnO. Electrical measurements suggest that an excess of Mn probably exists at grain boundaries, either as a very thin second phase or as an amorphous film, which could benefit grain boundary diffusion, therefore promoting the grain growth of ZnO.     

Grain growth kinetics of 3 mol. % yttria-stabilized zirconia during flash sintering

Grain growth kinetics of dense 3 mol. % yttria-stabilized zirconia (3YSZ) ceramics during both DC flash sintering and conventional annealing were investigated using the grain size as a marker of microstructure evolution. The results indicated faster grain growth under greater current density. In contrast to conventionally annealed specimen, the grain boundary mobility was enhanced by almost two orders of magnitude with the applied electric current, revealing that joule heating alone was not sufficient to account for the experimental results. Instead, activation energy for grain growth decreased significantly due to electro-sintering. Systematic characterization of graded microstructure further indicated that local oxygen vacancies and specimen temperature were responsible for a grain size transition. Based on electrochemical reaction involved in flash sintering, grain size reduction at the cathode was proposed to be attributed to the local rearrangement of lattice cations and generated oxygen ions.     

固相反应法制备纳米ZnO及其晶粒生长动力学

以乙酸锌和草酸为原料,采用低热固相化学反应法制备纳米氧化锌的前体,通过微波和马弗炉两种焙烧方式焙烧制备得到纳米氧化锌,考察了焙烧温度和时间对纳米氧化锌粒径的影响。使用透射电镜、热重-差热、傅里叶变换红外光谱仪和X射线衍射仪对前体和纳米ZnO进行表征;采用晶粒生长动力学唯象理论计算得出纳米氧化锌在这两种焙烧方式下的晶粒生长动力学规律。结果表明,前体为ZnC2O4?2H2O,随着焙烧温度的提高,纳米氧化锌晶粒迅速长大,在相同焙烧温度和时间下,微波焙烧氧化锌的晶粒尺寸要明显大于常规焙烧方式。微波焙烧和常规焙烧下氧化锌的晶粒生长平均动力学指数分别是6.114和6.858,晶粒生长的平均活化能分别为70.67 kJ/mol和52.13 kJ/mol。     

Structural,optical and magnetic behavior of (Pr,Fe) co-doped ZnO based dilute magnetic semiconducting nanocrystals

The development of ZnO-based dilute magnetic semiconductor nanostructures co-doped with rare-earth and transition metals has attracted substantial attention for spintronics application. In this work, Pr (1%) and Fe (1%, 3%, and 5%) co-doped ZnO nanoparticles (NPs) were synthesized via co-precipitation method, and their structural, morphological, optical, photoluminescence, and magnetic properties were investigated. The single-phase wurtzite hexagonal crystal structure of all samples was detected via X-ray diffraction. Morphological analysis revealed spherical shape of the NPs with an average size in 20–50 nm range. The ultraviolet (UV)–visible measurements showed a redshift in the UV band and a slight change in the bandgap of the co-doped NPs. Fourier transform infrared analysis proved the existence of different functional groups in all synthesized NPs. X-ray photoelectron spectroscopy confirmed that Pr and Fe ions incorporated in the host ZnO lattice exhibit Pr³⁺ and Fe³⁺ oxidation states, respectively. Photoluminescence analysis showed that incorporated ions induce characteristic emission bands and structural defects in the synthesized NPs. Magnetic characterization indicated that the ZnO NPs exhibit a diamagnetic nature. However, the (Pr, Fe) co-doped NPs exhibit ferromagnetism at room temperature because of the interactions between Pr³⁺ and Fe³⁺ ions and trapped electrons mediated by bound magnetic polarons. Excellent optical and magnetic properties of synthesized samples may render them promising candidates for spintronics applications.     

青霉素亚砜结晶生长与成核动力学

利用Mydlarz 和 Jones 模型（MJ2）,对乙酸丁酯中青霉素亚砜的成核与生长动力学进行研究。通过矩量法对MJ2模型进行处理后,利用晶体产品的粒度分布计算得到青霉素亚砜的生长速率与成核速率,然后利用最小二乘法拟合回归求解出成核与生长动力学方程参数。通过实验设计考察了过饱和度、温度与搅拌速度对青霉素亚砜晶体成核和生长过程的影响。研究表明青霉素亚砜晶体生长速率随过饱和度比的增加呈现指数型增长,确定青霉素亚砜晶体生长属于晶体表面生长控制过程。由于高速搅拌会增加青霉素亚砜晶体的破碎,促进了二次成核过程,随着搅拌速度的增加,晶体生长速率出现小幅下滑,而成核速率则明显升高。青霉素亚砜成核与生长动力学研究将有助于工业生产过程优化。     

Grain growth kinetics in microwave sintered graphene platelets reinforced ZrO2/Al2O3 composites

The grain growth kinetics and mechanical properties of graphene platelets(GPLs) reinforced ZrO₂/Al₂O₃(ZTA) composites prepared by microwave sintering were investigated. The calculated grain growth kinetics exponent n indicated that the GPLs could accelerate the process of the Al₂O₃ columnar crystal growth. And the grain growth activation energy of the Al₂O₃ columnar crystal indicated that the grain growth activation energy of the GPLs doped ZTA composites is much higher than those of pure Al₂O₃ and ZTA in microwave sintering. The optimal mechanical properties were achieved with 0.4?vol% GPLs, whose relative density, Vickers hardness and fracture toughness were 98.76%, 18.10?GPa and 8.86?MPa?m^1/2, respectively. The toughening mechanisms were crack deflection, bridging, branching and pull-out of GPLs. The results suggested that GPLs-doped are good for the Al₂O₃ columnar crystal growth in the ZTA ceramic and have a potentially improvement for the fracture toughness of the ceramics.     

Structural evolution,grain growth kinetics and microwave dielectric properties of Li2Ti1-x(Mg1/3Nb2/3)xO3

Li₂Ti_1-x(Mg_1/3Nb_2/3)_xO₃ ceramics were prepared by conventional solid state process. Their structural evolution, grain growth kinetics and microwave dielectric properties have been studied in this paper. The results show that continuous solid solution could be formed within the experiment compositional range. The structure changed from long range ordered monoclinic into short range ordered cubic phase as the increase in x. Small levels of substitution for Ti⁴⁺by (Mg_1/3Nb_2/3)⁴⁺ slightly decreased the dielectric permittivity, while considerably improved the Q × f value. The temperature coefficient of resonant frequency changed from positive into negative value. The grain growth kinetics during sintering process and Q × f value of the sintered body were affected by different calcining temperature of mixed powders. Excellent combined microwave dielectric properties with ε_r ～21.0, Q × f ～ 200 000 GHz and τ_f value of ?1 ppm/ °C could be obtained after optimizing calcining temperature for the x = 0.24 composition after sintering at 1250 °C/2 h.     

Microstructure-related piezoelectric properties of a ZnO film grown on a Si substrate

We investigated the effect of grain size on the piezoelectric properties of ZnO using films of different grain sizes and a fixed thickness of 800 nm deposited on a Si substrate by pulsed laser ablation in the temperature range of 300–700 °C. All of the deposited films have a crystal structure with a c-axis orientation. The grain size of the grown films, characterized by transmission electron microscopy (TEM), increases with the deposition temperature. In contrast, their piezoelectric efficiency (PE, d₃₃), characterized by piezoelectric force microscopy (PFM), was found to initially increase with the deposition temperature up to 500 °C, after which it decreased with further increases in temperature. The maximum PE value is observed for the film deposited at 500 °C with a grain size of approximately 60 nm. The peculiar PE behavior observed was theoretically explained by a competition between the contribution of the c-axis orientation favoring a larger d₃₃ value due to the enhanced static asymmetry and the strong grain size effect that influences the piezoelectric polarization as a result of domain motion.     

Hot pressing of nanocrystalline zinc oxide compacts: Densification and grain growth during sintering

Sintering behavior of nanocrystalline zinc oxide (ZnO) powder compacts using hot pressing method was investigated. The sintering conditions (temperature and total time) and results (density and grain size) of two-step sintering (TSS), conventional sintering (CS) and hot pressing (HP) methods were compared. The HP technique versus CS was shown to be a superior method to obtain higher final density (99%), lower sintering temperature, shorter total sintering time and rather fine grain size. The maximum density achieved via HP, TSS and CS methods were 99%, 98.3% and 97%, respectively. The final grain size of samples obtained by HP was greater than that of TSS method. However, the ultra-prolonged sintering total time and the lower final density (88 ks and 98.3%) are the drawbacks of TSS in comparison with the faster HP (17 ks and 99%) method.     

Structural and optical properties of a radio frequency magnetron-sputtered ZnO thin film with different growth angles

This study introduces optical properties of a columnar structured zinc oxide [ZnO] antireflection coating for solar cells. We obtained ZnO films of columnar structure on glass substrates using a specially designed radio frequency magnetron sputtering system with different growth angles. Field-emission scanning electron microscopy was utilized to check the growth angles of the ZnO films which were controlled at 0°, 15°, and 30°. The film thickness was fixed at 100 nm to get a constant experiment condition. Grain sizes of the ZnO films were measured by X-ray diffraction. A UV-visible spectrometer was used to measure the transmittance and reflectance of the ZnO film columnar structures as a function of the growth angles.     

Analysis of structural,optical and magnetic properties of Fe/Co co-doped ZnO nanocrystals

In this paper, the structural, optical and magnetic properties of pure ZnO and Fe/Co co-doped ZnO nanoparticles are presented. Rietveld refinement of XRD pattern revealed the single phase wurtzite structure for prepared samples. FTIR study confirmed the formation of tetrahedral coordination between zinc and oxygen ions. SEM and TEM techniques were used to examine the morphology of samples. The absorption spectra showed the decrease in optical energy band gap with Fe/Co co-doping in ZnO. PL spectra demonstrated five peaks correspond to the ultraviolet region, violet, violet-blue, blue-green and green in the visible region. Emission peak in the UV region is attributed to near band-edge excitonic emission. Other four emission peaks in PL spectra are related to different defect states. M-H curve showed room temperature ferromagnetic (RTFM) behaviour of doped ZnO sample. This paper enhances the understanding of structural, optical and magnetic properties of Fe/Co co-doped ZnO nanocrystals for application in spintronics, solar cells, and ceramics.     

Effect of silica doping on the densification and grain growth in zinc oxide

The ability of silica (SiO₂) in controlling the densification and grain growth behavior of nano crystalline zinc oxide (ZnO) has been systematically studied. It has been observed that SiO₂ acts as a sintering inhibitor in the ZnO–SiO₂ system up to 4 wt.% limiting value beyond which densification behavior of the system remains almost unchanged, especially above 1100 °C. The addition of SiO₂ to ZnO retards grain growth which in turn results a finer ultimate grain size as compared to the undoped ZnO. However, stabilization in grain size occurs at ≥4 wt.% SiO₂ addition. It has been observed that SiO₂ incorporation changes the grain growth mechanism up to 4 wt.% addition, beyond which no remarkable changes was noticed. The grain growth (n) shows distinctly different slopes as a function of sintering time for the SiO₂ doped ZnO systems than undoped ZnO. The different slopes tend to indicate that different diffusion mechanisms and probably the formation of a secondary phase (Zn–Si–O) at the grain boundary control the densification and grain growth. The thermal expansion coefficient of the system has been found to decrease substantially beyond 4 wt.% SiO₂ addition to ZnO.     

Enhancing the magnetic and antibacterial properties of ZnO nanopowders through Mn+Co doping

Undoped and doubly (Mn+Co) doped ZnO nanopowders were synthesized with different doping levels of Co (1, 2, 3, 4 and 5 at%) and constant Mn doping level (10 at%) using a simple soft chemical route. XRD profiles confirmed that the synthesized material is nanocrystalline ZnO with hexagonal wurtzite structure. No peaks other than the characteristic ZnO peaks were observed in the XRD pattern confirming the absence of any secondary phase. Antibacterial activities of synthesized ZnO nanopowders were tested against Staphylococcus aureus bacteria using agar well diffusion method. It was found that the antibacterial efficiency of the doubly doped ZnO nanopowders was remarkably high when the Co doping level was 5 at%. The obtained PL, SEM and TEM results are corroborated well with the antibacterial activity. Magnetic measurements showed that undoped ZnO sample exhibits diamagnetic behavior and as the Co doping level increases, the nanopowder behaves as a ferromagnetic material.     

Ni/ZnO吸附剂上汽油反应吸附脱硫本征动力学

采用小型固定床反应器,对制备的Ni/ZnO吸附剂的动力学进行测定,动力学实验基本条件为:以噻吩和正辛烷混合物作为模拟汽油,反应压力(0.4~0.8)MPa,反应温度(330~370)℃,氢油体积比70∶1,空速5h-1。在消除吸附剂内、外扩散影响的条件下,通过设计正交实验,得到固定床反应条件下的动力学实验数据。根据幂函数型速率方程,对实验数据进行多元非线性拟合,得到动力学方程为:r=0.0229×e-22528.51/RTp0.0013Hp0.053Sc0.95ZnO,并对模型进行统计检验。结果表明,该模型对表面反应控制阶段具有较好的适用性。     

Electric and microstructural characteristics of bulk ZnO fabricated by underwater shock compaction

An underwater shock compaction of pure zinc oxide (ZnO) powder has been performed. This technique uses an underwater shock wave generated by detonation of an explosive. Shock pressure used in this work was about 10 GPa. The morphology and structure of shock-consolidated ZnO was investigated by X-ray diffraction (XRD) method and scanning electron microscopy (SEM). The density and impedance characteristics of shock-consolidated ZnO were measured by Archimedes method and Nyquist plot method, respectively. The shock-consolidated ZnO without visible cracks was successfully obtained. It was confirmed that the shock-consolidated ZnO had 99% of theoretical density without grain growth and high grain boundary resistivity in comparison with the commercial sintered ZnO.     

Morphological,magnetic and EPR studies of ZnO nanostructures doped and co-doped with Ni and Sr

Herein, were analyzed the effects of Sr and Ni addition on the morphological, electronic and magnetic properties of ZnO nanoparticles synthesized by the sol gel route. Morphological analysis showed agglomerated particles with nonuniform shapes (polyhedral, hexagonal and spherical) and the average size distributions were calculated counting more than 100 nanoparticles (sizes between 43 and 75 nm). For pure ZnO sample, the selected area electron diffraction (SAED) showed bright and concentric discontinuous diffraction rings, while the co-doped samples, presented patterns well-organized concentric circular rings, typical of reflection of regularly arranged atoms. The electron paramagnetic resonance (EPR) was employed to analyze the intrinsic defects due to the dopant inclusion. In addition, the EPR spectra were simulated using the spin quantum number (S = 1) for Ni²⁺ to understand the experimental results. Ni ions were used as a local probe in the comparative study by EPR, capturing subtle modifications in the zero-field interactions due to induced strain in the lattice. Microscopically the changes observed, through the EPR study, result from the reduction of the axial distortion of the ligand field and increasing in the distortion perpendicular to the principal axis. Magnetic study showed a typical significant diamagnetism at 300 K, while a paramagnetic contribution was more evident at 4 K. The work contributes to clarify the complex magnetic response in ZnO nanoparticles doped and co-doped with Sr and Ni.     

Anisotropic growth kinetics and electric properties of PZT-5H single crystal by solid-state crystal growth method

The PZT-5H single crystal growth on [111]c-, [110]c-, and [001]c-oriented seed crystal by solid-state crystal growth (SSCG) method was investigated. The growth rate of PZT-5H single crystal strongly depends on seed crystal orientation and annealing time. The mean growth distance is 682, 620, and 93 μm for [111]c-, [110]c-, and [001]c-oriented PZT-5H single crystal grown at 1150°C for 8 h, respectively. The growth kinetics of SSCG-grown PZT-5H single crystal was discussed. It is found that the growth of single crystal is driven by the solubility difference between the matrix grains and single crystal growth front interface, arising from the local curvature and the crystallographic directions dependent solubility. The growth of [001]c-oriented PZT-5H single crystal was mainly contributed from the difference solubility arising from the local curvature of growth front interface, while the growth of [111]c- and [110]c-oriented PZT-5H single crystal was mainly contributed from the difference solubility between {111} and {110} plane of single crystal and matrix grains. The piezoelectric coefficient d₃₃ of up to 1028pC/N (about 50% larger than that of the same component ceramic) was obtained in a [110]c-oriented PZT-5H single crystal with a Curie temperature of about 230°C. The large field piezoelectric constants d₃₃* of up to 1160 pm/V (about 50% larger than that of the same component ceramic) at 15 kV/cm was also obtained in [110]c-oriented PZT-5H single crystal with a large strain of 0.18%. This work deepens our understanding on the growth kinetics of SSCG and pushes the way of growth of soft PZT single crystal by SSCG.     

Controllable electrochemical synthesis of La/ZnO hierarchical nanostructures and their optical and magnetic properties

Here we presented a facile electrochemical deposition route for the controllable preparation of La³⁺/ZnO hierarchical nanostructures, such as flower-like nanostructures consisted of nanorods, flower bundles, and hexagonal nanorods with nests at the top. These prepared La³⁺/ZnO deposits were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV-vis spectrophotometer, and photoluminescence spectroscopy. The formation process of La³⁺-doped ZnO and the growth mechanisms of La³⁺/ZnO hierarchical nanostructures were discussed. The UV and PL spectra measurements show that the surface morphologies of La³⁺/ZnO deposits have an obvious effect on their optical properties and we can easily adjust their optical properties as well as La³⁺/ZnO nanostructures by changing electrochemical deposition parameters. In addition, the magnetic properties of La³⁺/ZnO deposits were also investigated.     

Impact of the Zr-substitution on phase composition,structure, magnetic,and microwave properties of the BaM hexaferrite

Rapid developments in information technologies and a large rise in electrical and electronic equipment have generated different forms of electronic environmental contamination. Microwave absorption materials are important to avoid the damage that can be caused by electromagnetic radiation. A necessary condition for the absorption of the most incoming radiation is balanced wave impedance at the air/shield interface, which depends on the studied materials' magnetic and electrical properties. The paper introduces the preparation of BaFe_12-xZr_xO₁₉ (x = 0.1, 0.3, 0.6, 0.9, and 1.2) using a solid-state reaction technique. The studied samples were examined by X-ray diffraction, scanning electron microscopy, vibrating sample magnetometer, and a vector network analyzer. The studied samples showed that controlling the grain size and the prepared samples' magnetic properties play an important role in enhancing the microwave radiation absorption. The examined samples can be a promising absorption material in electromagnetic shielding applications.     

Nb5+ ion substitution assisted the magnetic and gyromagnetic properties of NiCuZn ferrite for high frequency LTCC devices

Nowadays, developing nickle zinc ferrites with excellent magnetic and gyromagnetic properties are of great importance for solving the matching problem of 5G communication system. However, much is discussed about soft magnetic properties, but little is reported gyromagnetic properties that is critical for microwave device applications. Herein, Nb⁵⁺ ions substituted Ni_0.29Cu_0.18Zn_0.53Nb_xFe_2-xO₄ (x = 0.00-0.05), possessing high saturation magnetization, approriate initial permeability, high cut-off frequency and low ferromagnetic resonance linewidth (@9.55 GHz), were synthesized by low-temperature firing (900 °C). The phase structure and morphology evolutions were studied in detail. The results of morphology observations revealed that Nb⁵⁺ substitution has significant role in determining produce compact and uniform microstructures of NiCuZn ferrites via suppress the grain growth, which further corresponding enhance the magnetic and gyromagnetic properties. As a result, a uniform and compact grain size can be obtained, corresponding to the change of magnetic and gyromagenetic properties have different trends. Enhanced magnetic and gyromagnetic performance including high initial permeability (μ' = 203 @1 MHz), saturation magnetization (4πM_s = 3966 Gauss) and low ferromagnetic resonance linewidth (ΔH = 203 Oe) of the NiCuZn ferrites is achieved though adjusting Nb⁵⁺ ions substitution. More importantly, this work not only for low temperature co-fired ceramic (LTCC) technology but also for high frequency and microwave frequency devices including phase shifter and radars.