Larger Average Grain Research Articles

Iron-ion irradiation effects on microstructure of yttrium oxide coating fabricated by magnetron sputtering

Ceramic coatings have been investigated as tritium permeation barrier for several decades; however, there is little knowledge about irradiation effects on the coatings. In this study, yttrium oxide coatings were fabricated on reduced activation ferritic/martensitic steel substrates by radio frequency reactive magnetron sputtering, and their microstructures were investigated after iron-ion irradiation under various parameters with damage concentration of up to 20 displacement per atom. The formation of voids and an amorphous layer was confirmed in all the irradiated samples. In addition, it was found that irradiation-induced grain growth proceeded with damage concentration, and the increase of grain size was proportional to damage concentration. Furthermore, a layer with few voids formed between the crystallized and amorphous layers for the irradiated samples with higher incident energy or higher dose. Defect recovery and heat-driven grain growth and/or crystallization occurred for the sample irradiated at 500 °C, resulting in a larger average grain size than those irradiated at room temperature. Further consideration of irradiation effects to the coatings under fusion-relevant irradiation conditions is necessary.

Twinning and slip behaviors and microstructural evolutions of extruded Mg-1Gd alloy with rare-earth texture during tensile deformation

An extruded Mg-1Gd alloy with a non-basal texture, whose basal poles are tilted 60.9° from the extrusion direction (ED), exhibits a high room-temperature tensile elongation of 37.2%. This study investigates the active deformation mechanisms and microstructural evolutions of this highly ductile extruded alloy during tensile deformation through in situ electron backscatter diffraction analysis. When tensile strain is applied along the ED, a small amount of {10-12} twins is formed at the early stage of deformation, and the twins gradually grow with increasing applied strain. However, {10-11} twins and {10-11}-{10-12} twins, which are generally observed in extruded Mg alloys with a typical basal fiber texture, are not formed during deformation. The tilted initial texture is favorable for basal slip, and therefore, basal slip is vigorously activated during tension. As a consequence, the average angle between the c-axis of the grains and the ED increases from 60.9° to 66.3° as the applied tensile strain increases from 0% to 30%. Prismatic slip is also activated during tension, which is confirmed by the gradual increase in the rotation angle of the prismatic poles around the <0001> axis during deformation. The activation of prismatic slip causes a significant reduction in the texture intensity of the alloy during deformation. The high ductility of the Mg-1Gd alloy is attributed mainly to the activation of {10-12} twinning, which is beneficial to elongation, instead of the activation of {10-11} twinning, which is detrimental to elongation, and the promoted activation of basal and non-basal slips. Furthermore, microstructural characteristics such as the fully recrystallized structure, large average grain size, and absence of second-phase particles also contribute to the high ductility of the alloy.

Reduced leakage current, enhanced ferroelectric and dielectric properties in Mn-doped BiFeO3 thin film composited with TiO2 layers

Abstract The 2 mol% Mn-doped Bi1.05FeO3 (abbreviated as BFOMn, S0), BFOMn composited films with TiO2 layer at the surface of BFOMn (S1), and on the interface between BFOMn film and substrate (S2), as well as at the both sides of the BFOMn film (S3) were prepared on indium tin oxide (ITO)/glass substrates through a chemical solution deposition process. The effects of TiO2 layers deposited at different positions on microstructure, insulating, ferroelectric and dielectric performances are fully investigated. The crystallized perovskite structures without any secondary phases are well maintained in all samples. Increased grain sizes can be achieved with the introduction of TiO2. Among these films, S3 has large average grain size and possesses decreased leakage current density of 7.2 × 10−5 A/cm2 under 400 kV/cm, relatively large remanent polarization (Pr) value of 82.3 μC/cm2 under 3333 kV/cm at 10 kHz, larger dielectric constant (∼ 330) and smaller dissipation factor (∼ 0.04) at 100 kHz. These results demonstrate that introducing TiO2 layers into appropriate positions can be a feasible way to improve the microstructure and enhance the electrical properties of BFO-based films.

Enhanced multiferroic properties of Bi0.85Nd0.15FeO3 ceramics with excess Bi2O3

Multiferroic Bi(1+x)×0.85Nd0.15FeO3 (BNF) ceramics with various Bi contents are prepared by conventional solid state reaction, and the effects of excess Bi on the structure, morphology, dielectric, ferroelectric, and magnetic properties are investigated. XRD patterns show the coexistence of rhombohedral and orthorhombic phase in all BNF ceramics due to the doping of Nd3+ ions. Bi2Fe4O9 and Bi2O3 impurity can be observed in x = 0 and x = 5%, 7.5% ceramics, respectively. Surface morphologies are closely related to the Bi content and x = 2.5% sample exhibits the largest average grain size of ∼6.72 μm. The leakage current density has been decreased by 3–4 orders of magnitudes through excess Bi. The x = 2.5% sample shows good ferroelectric property with typical hysteresis loop and a large remnant polarization of about 42 μC/cm2 at 150 kV/cm. The P-E hysteresis deteriorates in x = 5% and x = 7.5% ceramics. The PbZrO3-like superstructure related to 1/4(hh0)p diffraction spots in SAED pattern can be found in all BNF ceramics and the number of grain with superstructure observed in each sample decreases as the Bi content increases. As Bi content increases, the remnant magnetization decreases at first, and then increases. Conversion-electron Mossbauer study have ruled out the impacts of Fe2+, Fe4+, or γ-Fe2O3 on the magnetic properties, suggesting that the weak ferromagnetism comes from the destroy of spin cycloid through substitution of Bi3+ ions with Nd3+ ions. Excessive Bi3+ ions have weakened the effect of Nd3+ ions on suppression of spin cycloid and resulted in the degradation of magnetic properties. The slight improvement of magnetic properties in x = 7.5% sample is considered to attribute to Fe vacancies induced by excessive Bi.

Friction stir welding of Monel alloy at different heat input conditions: Microstructural mechanisms and tensile behavior

The mechanisms governing the microstructural evolution during friction stir welding of Monel at different heat inputs and the corresponding mechanical properties were investigated. In the low heat input condition, both continuous and discontinuous dynamic recrystallizations caused the formation of fine grains with an average grain size of 1.7 μm and closely random texture. A high heat input condition resulted in larger average grain size of 23.5 μm with shear texture by only the continuous dynamic recrystallization. Low heat input led to the simultaneous increase of strength and elongation. The origins of the tensile behavior of the joints have been discussed.

Magnetic properties and microstructures of a Ni-Zn ferrite ceramics co-doped with V2O5 and MnCO3

The present work investigated the effect of the addition of V2O5 and MnCO3 on the microstructure and magnetic properties of Ni-Zn ferrite ceramic samples prepared by a conventional ceramic sintering method at different temperatures. With this aim, a series of samples were prepared by varying the loadings of V2O5-MnCO3 (un-doped, 0.4–0.1 wt%, 0.1–0.4 wt%, 0.2–0.3 wt%, 0.3–0.2 wt%, and 0.5–0.1 wt%, denoted as sample 1, sample 2, sample 3, sample 4, sample 5, and sample 6, respectively). The initial permeability and power loss of the different Ni-Zn ferrites were investigated with respect to the sintering temperature. The V2O5 and MnCO3 dopants significantly improved the initial permeability and power loss characteristics of the Ni-Zn ferrite at frequencies ≥0.5 MHz. When sintered at 1100 °C, sample 2 showed a maximum initial permeability of 931.23 H/m at a frequency of 1 MHz combined with a minimum power loss of 339.2 kW/m3. Co-doping with V2O5 and MnCO3 also resulted in the sintered samples with larger average grain sizes and higher density, while the sintering temperature of Ni-Zn ferrites was significantly reduced.

Influence of Li&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;CO&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt; and ZnO Nanoparticle on Microstructure and Magnetic Properties of Low-Temperature Sintering LiZnTiBi Ferrites for High-Frequency Applications

LiZnTi ferrite ceramics with high saturation flux density (Bs), large remanence ratio (Br/Bs) and high saturation magnetization (4πMs) is a vital material for high frequency devices. In the present work, we prepared uniform and compact LiZnTiBi ferrite with large average grain size (>30μm) at 900°C. Firstly, the hybrid materials, including Li2CO3, ZnO, TiO2, Bi2O3 and Fe2O3, were pre-sintered at 850°C at O2 atmosphere. Next, composite additives composited of Li2CO3 and ZnO nanoparticles were added to control grain growth. The influences of the Li2CO3 and nano-ZnO (LZ) on the microstructure and magnetic properties of LiZnTiBi ferrite, especially for grain size, have been analyzed. SEM images demonstrated that moderate LZ additives (x=0.75 wt%) can prevent abnormal grains. Also, the ferrite samples possess compact microstructures. The phenomenon indicated that the LZ additive is a good sintering aid for low-temperature sintering LiZnTiBi ferrites. XRD patterns showed that all samples have a pure spinel phase. The magnetic properties, including Bs, Br/Bs and 4πMs, have weak change when LZ additives were added. However, due to smaller average grain size, the coercivity (Hc) gradually increased. Thus, a low-temperature sintering LiZnTiBi ferrite with high saturation flux density (Bs=311.10 mT), large remanence ratio (Br/Bs=0.86), low coercivity (Hc=244.6 A/m) and high saturation magnetization (Ms=75.40) was obtained when 1.00 wt% LZ additive was added. More important, the LiZnTiBi ferrite possessed uniform average grain. Such a sintering method (i.e., adding composite additive to control abnormal grain) should also promote synthesis of other advanced ceramics for practical applications.

Molecular Dynamics Simulation of Nanoscale Abrasive Wear of Polycrystalline Silicon

In this work, molecular dynamics simulations of the nanoscratching of polycrystalline and singlecrystalline silicon substrates using a single-crystal diamond tool are conducted to investigate the grain size effect on the nanoscale wear process of polycrystalline silicon. We find that for a constant indentation depth, both the average normal force and friction force are much larger for single-crystalline silicon compared to polycrystalline silicon. It is also found that, for the polycrystalline substrates, both the average normal force and friction force increase with increasing grain size. However, the friction coefficient decreases with increasing grain size, and is the smallest for single-crystalline silicon. We also find that the quantity of wear atoms increases nonlinearly with the average normal load, inconsistent with Archard’s law. The quantity of wear atoms is smaller for polycrystalline substrates with a larger average grain size. The grain size effect in the nanoscale wear can be attributed to the fact that grain boundaries contribute to the plastic deformation of polycrystalline silicon.

Regulation of Substrate-Target Distance on the Microstructural, Optical and Electrical Properties of CdTe Films by Magnetron Sputtering.

Cadmium telluride (CdTe) films were deposited on glass substrates by direct current (DC) magnetron sputtering, and the effect of substrate-target distance (Dts) on properties of the CdTe films was investigated by observations of X-ray diffraction (XRD) patterns, atomic force microscopy (AFM), UV-VIS spectra, optical microscopy, and the Hall-effect measurement system. XRD analysis indicated that all samples exhibited a preferred orientation along the (111) plane, corresponding to the zinc blende structure, and films prepared using Dts of 4 cm demonstrated better crystallinity than the others. AFM studies revealed that surface morphologies of the CdTe films were strongly dependent on Dts, and revealed a large average grain size of 35.25 nm and a high root mean square (RMS) roughness value of 9.66 nm for films fabricated using Dts of 4 cm. UV-VIS spectra suggested the energy band gap (Eg) initially decreased from 1.5 to 1.45 eV, then increased to 1.68 eV as Dts increased from 3.5 to 5 cm. The Hall-effect measurement system revealed that CdTe films prepared with a Dts of 4 cm exhibited optimal electrical properties, and the resistivity, carrier mobility, and carrier concentration were determined to be 2.3 × 105 Ω∙cm, 6.41 cm2∙V−1∙S−1, and 4.22 × 1012 cm−3, respectively.

Boosting the efficiency of carbon-based planar CsPbBr3 perovskite solar cells by a modified multistep spin-coating technique and interface engineering

All-inorganic CsPbBr3 perovskite solar cells (PSCs) have attracted tremendous attentions in the photovoltaic field these days in view of their outstanding stability, especially thermal stability. However, the bromide-rich perovskite, such as CsPbBr3, always suffer from a low phase-purity and poor morphology synthesized by traditional two-step deposition route. Herein, we demonstrate a facile multistep spin-coating strategy to fabricate high-quality CsPbBr3 films on the low-temperature processed compact TiO2 (c-TiO2) electron transport layer (ETL) of the carbon-based PSCs. As-prepared films exhibit more homogeneous with higher CsPbBr3-phase purity and larger average grain sizes up to 1 µm, compared to those prepared through traditional two-step deposition process. The champion power conversion efficiency (PCE) of the planar CsPbBr3 PSC is boosted from 7.05% to 8.12%, getting an increase by 15.2%, due to the increased crystallinity and light-harvesting ability as well as reduced trap states of the CsPbBr3 film. To further enhance the device performance, a SnO2 thin layer with much higher carrier mobility than TiO2 is introduced to passivate the c-TiO2 ETL. It is found that the SnO2 layer can not only improve the surface morphology of the ETL, but also reduce the current shunting pathways in the c-TiO2. The TiO2/SnO2 bilayered ETL possesses a superior electron extraction capability, beneficial to the charge transport and suppression of the interfacial trap-assisted recombination. The best-performing TiO2/SnO2-based CsPbBr3 PSC delivers an excellent fill factor of 0.817 and a high PCE of 8.79%, which is the highest efficiency for planar CsPbBr3 PSCs reported to date. More importantly, the unencapsulated all-inorganic PSCs show a promising humidity and thermal stability with no decline in efficiency when stored in ambient air at room temperature (25 °C) for over 1000 h and 60 °C for one month, respectively. Our work pave the ways for practical applications of cost-effective, highly efficient and stable all-inorganic PSCs.

Study on Fabrication of ZnO Waveguide Layer for Love Wave Humidity Sensor Based on Magnetron Sputtering.

The ZnO waveguide layer for the Love wave humidity sensor was fabricated by radio frequency (RF) magnetron sputtering technique using ZnO as the target material. To investigate the effect of RF magnetron sputtering temperature on the ZnO waveguide layer and Love wave device, a series of Love wave devices with ZnO waveguide layer were fabricated at different sputtering temperatures. The crystal orientation and microstructure of ZnO waveguide was characterized and analyzed, and the response characteristics of the Love wave device were analyzed by network analyzer. Furthermore, a humidity measurement system is designed, and the performance of the Love wave humidity sensor was measured and analyzed. The research results illustrate that the performance of the ZnO waveguide layer is improved when the sputtering temperature changes from 25 °C to 150 °C. However, when the sputtering temperature increases from 150 °C to 200 °C, the performance of the ZnO waveguide layer is degraded. Compared with the other sputtering temperatures, the ZnO waveguide layer fabricated at 150 °C has the best c-axis orientation and the largest average grain size (53.36 nm). The Love wave device has the lowest insertion loss at 150 °C. In addition, when the temperature of the measurement chamber is 25 °C and the relative humidity is in the range of 10% to 80%, the fabricated Love wave humidity sensor with ZnO waveguide layer has good reproducibility and long-term stability. Moreover, the Love wave humidity sensor has high sensitivity of 6.43 kHz/RH and the largest hysteresis error of the sensor is 6%.

Effects of calcination temperature and flux doping on the microstructure and magnetic properties of low-temperature-fired NiCuZn ferrites

The correlative influences of calcination temperature and Bi2O3 doping content on the microstructure and magnetic properties of the low-temperature-fired NiCuZn ferrites were investigated. For ferrites with relatively low calcination temperatures, such as 750 °C and 850 °C, Bi2O3 doping easily triggered inhomogeneous grain growth. Controlling the flux amount to lower than the ‘critical’ value, which triggered abnormal grain growth, was preferred to obtain good magnetic properties. For ferrites with relatively high calcination temperatures, such as 950 °C and 1050 °C, flux doping was not prone to stimulating abnormal grain growth. Thus, the optimum doping content could be added when the highest sintered density was detected. With excessive Bi2O3 concentrations, low-temperature-calcined ferrites could produce homogeneous microstructures with a relatively large average grain size. By contrast, high-temperature-calcined ferrites could form homogeneous microstructures with a relatively small average size, which favoured a high Q-factor and was more favourable for high frequency applications.

Efficient and stable planar p-i-n perovskite solar cells by doping tungsten compound into PEDOT:PSS to facilitate perovskite crystalline

The photovoltaic efficiency and stability of planar p-i-n perovskite solar cells (PVSCs) are largely dependent on charge carrier dynamics and surface properties of hole transport layers (HTLs). Herein we introduce ammonium metatungstate hydrate (AMH) into poly(3,4-ethylenedio-xythiophene): poly(styrenesulfonate) (PEDOT:PSS) for the first time. The results showed that AMH dopant could not only enhance the conductivity of PEDOT:PSS film without impact its transmissivity, but also change the surface property of HTL after the annealing process of composite HTL. The composite HTL yields the perovskite with large average grain size, smooth and dense film. Consequently, the average power conversion efficiency (PCE) of 14.61% was achieved in PVSCs based on the optimal concentration of AMH modified PEDOT:PSS, with improved short-circuit current (JSC) and fill factor (FF). Meanwhile, the ambient stability of AMH modified devices is also enhanced by more than 3 times compared with the control devices.

Strategic improvement of Cu2SnS3 thin film by different heating rates and photoluminescence investigation

Cu2SnS3 (CTS) thin films have been synthesized on molybdenum-coated soda lime glass substrates by sulfurization the Cu-Sn alloy precursors grown by radio-frequency magnetron sputtering technique. Strategic improvement has been carried out on the composition, structural, morphological and optical properties of CTS thin films sulfurized by rapid heating rate and slow heating rate. The annealing heating rate can adjust the ratio of Cu/Sn, improve the crystallinity and surface morphology. The ratio of Cu/Sn is close to the stoichiometric composition of CTS under slow heating rate with more loss of Sn. Structural characterization exhibits the CTS thin film sulfurized by slow heating rate has a better crystallinity without secondary phase. The CTS thin film obtained at slow heating rate presents a larger average grain size and smooth surface. The optical band gap of CTS thin films is at the vicinity of 0.87 eV. Photoluminescence (PL) spectroscopy has been used to study the carrier recombination mechanism and the electronic structure of CTS thin film by excitation power and temperature dependent measurements. The peak observed from PL spectra of CTS thin film conforms to the donor-acceptor pair recombination luminescence.

Effects of selenium atmosphere on grain growth for CZTSe absorbers fabricated by selenization of as-sputtered precursors

Pure kesterite Cu2ZnSnSe4 (CZTSe) absorbers with a large average grain size are vital for high-efficiency CZTSe solar cells, which are greatly influenced by the annealing atmosphere. Sputtered CZTSe precursors were annealed in the presence and absence of a selenium-containing atmosphere, and these materials were incorporated into solar cells. When annealed in an Ar atmosphere, the CZTSe absorbers were found to be composed of small grains with the presence of voids and secondary phases. When H2Se was added into the chamber at a temperature of 550 °C, the CZTSe grains increased in size and the presence of the voids and secondary phases reduced. When H2Se was added at a lower temperature (300 °C) earlier in the annealing process, the average grain size increased further and device efficiencies were higher. When H2Se was continuously added into the chamber during the whole selenization process, the average grain size increased to approximately 2 μm, the undesired secondary phases were not detected and the efficiency of the CZTSe devices reached a maximum of 6.78%. This work showed that exposing the CZTSe precursors to a selenium atmosphere during annealing increased the average grain size and reduced the presence of undesirable secondary phases, thus improving the performance of CZTSe absorbers and solar cells.

Dielectric properties of CaCu2.9Zn0.1Ti4O12 ceramics by addition of Al2O3 nanoparticles

The CaCu3Ti4O12 (CCTO) and (1−x) CaCu2.9Zn0.1Ti4O12–xAl2O3 (0 ≤ x ≤ 0.02) ceramics were prepared via a conventional solid-state method. X-ray diffraction shows that (1−x) CaCu2.9Zn0.1Ti4O12–xAl2O3 ceramics sintered at 1110 °C for 6 h has a CCTO single phase. For the SEM studies of (1−x) CaCu2.9Zn0.1Ti4O12–xAl2O3 ceramics, the 0.985 CaCu2.9Zn0.1Ti4O12–0.015 Al2O3 ceramics has the largest average grain size, followed by CaCu2.9Zn0.1Ti4O12, 0.99 CaCu2.9Zn0.1Ti4O12–0.01 Al2O3, 0.98 CaCu2.9Zn0.1Ti4O12–0.02 Al2O3, CCTO, finally 0.995 CaCu2.9Zn0.1Ti4O12–0.005 Al2O3. When x = 0.015, the dielectric constant is 54,774, the dielectric loss is 0.18 at 1 kHz at room temperature, the grain boundary resistance (Rgb) is 4.7 × 104 Ω and the grain resistance (Rg) is 5.42 Ω. The variation of the loss tangent (tanδ) value of all the samples is consistent with the change of grain boundaries resistance. The results indicate that the nano-Al2O3 doping, which can increase the dielectric constant, has a promising application in enhancing dielectric properties of CCTO.

Study on the Effect of Oxygen Defects on the Electrical and Optical Properties of Thin Films.

SnO2 thin films grown directly on the Si substrate had larger average grain sizes as the power intensity increased, but the average grain size of the SnO2 thin films grown in oxygen atmosphere decreased as the power intensity increased. Hall measurement of pure SnO2 thin films showed that the carrier density increased with increasing power. However, upon annealing the SnO2 thin films, the carrier density decreased with increasing power owing to the formation of oxygen vacancies and the SiO2 layer between the Si substrate and SnO2 thin films. The photoluminescence (PL) of the SnO2 thin film grown in the oxygen atmosphere changed, and it was affected by the oxygen defects at the surface and interfaces of the thin film.

Photoconductive ZnO Films Printed on Flexible Substrates by Inkjet and Aerosol Jet Techniques

Zinc oxide (ZnO) thin films have remarkable versatility in sensor applications. Here, we report simple ink synthesis and printing methods to deposit ZnO photodetectors on a variety of flexible and transparent substrates, including polyimide (Kapton), polyethylene terephthalate, cyclic olefin copolymer (TOPAS), and quartz. X-ray diffraction analysis revealed the dependence of the film orientation on the substrate type and sintering method, and ultraviolet–visible (UV–Vis) absorption measurements revealed a band edge near 380 nm. van der Pauw technique was used to measure the resistivity of undoped ZnO and indium/gallium-codoped ZnO (IGZO) films. IGZO films showed lower resistivity and larger average grain size compared with undoped ZnO films due to addition of In3+ and Ga3+, which act as donors. A 365-nm light-emitting diode was used to photoirradiate the films to study their photoconductive response as a function of light intensity at 300 K. The results revealed that ZnO films printed by aerosol jet and inkjet techniques exhibited five orders of magnitude photoconductivity, indicating that such films are viable options for use in flexible photodetectors.

Understanding the Effect of Delay Time of Solvent Washing on the Performances of Perovskite Solar Cells.

Uniform and dense perovskite films were realized by the one-step solution-processing method combined with toluene washing. The influence of the delay time applied for toluene washing on the film quality of CH3NH3PbI3 (MAPbI3) was investigated in a comprehensive manner. The optimal delay time was experimentally observed at the critical point when the color of the film changes from transparent to hazy. A detailed X-ray diffraction study suggested that such a color change was caused by the emergence of the MAPbI3 crystal nucleus. This finding provides a convenient method to determine the optimal time accurately. With the optimal delay time, the most uniformly distributed MAPbI3 grains with the largest average grain size and the smoothest surface were obtained. Owing to the realization of homogeneous MAPbI3 films combined with full coverage of perovskite on the substrate achieved by toluene washing at the critical point, open-circuit voltage, short-circuit current, fill factor, and power conversion efficiency of 1.11 V, 18.24 mA/cm2, 77.47, and 15.54% were obtained.

Correlation between the microstructure and permeability stability of ferrite materials

Permeability stability is very important for ferrite materials used in modern electronic devices. In this study, different contents of Bi2O3–B2O3–SiO2–ZnO (BBSZ) glass were added to NiCuZn ferrite materials to obtain samples with different average grain sizes and grain boundary thicknesses. On the premise of obtaining the same permeability, this study determined that ferrite sample with a large average grain size and thick grain boundary width presented better permeability stability characteristics, including frequency stability, temperature stability, and DC-bias-superposition stability, than the sample with a small average grain size and thin grain boundary. This study subsequently established a model and theoretically demonstrated why the sample with a larger average grain size and thicker grain boundary width possessed superior permeability stability characteristics. This investigation provides a good guide for developing superior stable ferrite materials by improving microstructure characteristics.