Re-annealing Treatment Research Articles

Local charge regulation via selenium vacancies engineering in dielectric cobalt diselenide with enhanced microwave absorption

The weak electromagnetic loss capability of the single semiconductor material is difficult to meet the complicated electromagnetic environment nowadays, so vacancy engineering is employed to optimize the dielectric loss capability of CoSe2. Selenium vacancies are introduced into CoSe2 by re-annealing treatment, and the test results show that the selenium vacancies concentration enlarged with annealing temperature. The formation of selenium vacancies introduces a localized state in CoSe2, which enhances the capability of CoSe2 to trap charge carriers, and the increased conductivity contributes to the enhancement of the dielectric loss capability. Density Functional Theory (DFT) calculations demonstrate that the selenium vacancies disrupt the original charge equilibrium distribution of the CoSe2, and the non-recombined positive and negative charge centers induce a strong electric dipole polarization loss. Benefiting from the optimization of CoSe2 dielectric loss by the selenium vacancies engineering, RLmin of CoSe2-600 reaches −30.73 dB and the effective absorption bandwidth reaches 4.00 GHz at 1.8 mm. This study provides a simple and effective solution to optimize the microwave absorption performance of single-component microwave absorption materials.

Defect elimination to enhance photoluminescence and optical transparency of Pr-doped ceramics for self-calibrated temperature feedback windows

Pr-doped metal oxide polycrystalline transparent ceramics are highly desirable for photothermal window systems served in extreme environments, however, obtaining efficient photoluminescence together with high transparency in these ceramics is still posing serious challenges, which undoubtedly limits their applications. Here, Pr-doped Y₂Zr₂O₇ (YZO) transparent ceramics, as an illustrative example, are prepared by a solid-state reaction and vacuum sintering method. Owing to the elimination of defect clusters [ Pr_Y⁴⁺-O^2- - Pr_Y⁴⁺] and [Pr_Y⁴⁺ - e'] without introduction of impurities and additional defects, the fabricated YZO:Pr ceramics exhibit high transparency (74 %) and efficient photoluminescence (39-fold enhanced) after air annealing plus vacuum re-annealing treatment. Moreover, upon 295/450 nm excitation, the emission bands (blue, green, red, and dark red) from YZO:Pr ceramic present different temperature-dependent properties due to the thermal quenching channel generated by the intervalence charge transfer state (IVCT) between Pr³⁺ and Zr⁴⁺ ions. Furthermore, a self-calibrated temperature feedback window with same FIR model (I₆₁₃/I₅₀₃) under different excitation light sources (295 nm and 450 nm) is designed. The developed photothermal window operated in a wide temperature range (303 - 663 K) shows relatively high sensitivities (<em>S</em>_a and <em>S</em>_r reach 0.008 K^-1 at 663 K and 0.47 % K^-1 at 363 K, respectively), high repeatability (&gt; 98 %), and low temperature uncertainty (&lt; 3 K). This work presents a paradigm for achieving enhanced photoluminescence along with elevated transparency of lanthanides doped ceramics through vacuum re-annealing treatment engineering and demonstrates their promising potential for photothermal window systems.

Sintering temperature and atmosphere effects on electric and magnetic properties of multilayer FeSiCr alloy inductors

This study investigates the electric and magnetic properties of multilayer inductors made of FeSiCr alloy powders sintered at different temperatures and atmospheres. For FeSiCr alloy sintered in air, the semiconducting AgCrO2 phase formation has a great impact on the insulation resistance and withstands pulse voltage. The inductance for samples sintered in the air decreased with increasing sintering temperature. The insulation resistances were low for the samples sintered under a nitrogen atmosphere. However, re-annealing treatment in the air can increase insulation resistance. The inductance sequence for samples sintered under nitrogen atmosphere is 750 °C > 650 °C > 850 °C. Multilayer FeSiCr alloy inductors can be sintered under a nitrogen atmosphere to increase the inductance by suppressing nonmagnetic phase formation and improve the Q value by increasing the silver conductor continuity. After sintering, multilayer inductors can be re-annealed in the air to increase the resistance, and hence increase the ability to withstand pulse voltage.

Cu,N-Codoped Carbon Nanodisks with Biomimic Stomata-Like Interconnected Hierarchical Porous Topology as Efficient Electrocatalyst for Oxygen Reduction Reaction.

Metal,N-codoped carbon (M-N-C) nanostructures are promising electrocatalysts toward oxygen reduction reaction (ORR) or other gas-involved energy electrocatalysis. Further creating pores into M-N-C nanostructures can increase their surface area, fully expose the active sites, and improve mass transfer and electrocatalytic efficiency. Nonetheless, it remains a challenge to fabricate M-N-C nanomaterials with both well-defined morphology and hierarchical porous structures. Herein, high-quality 2D Cu-N-C nanodisks (NDs) with biomimic stomata-like interconnected hierarchical porous topology are synthesized via carbonization of Cu-tetrapyridylporphyrin (TPyP)-metal-organic frameworks (MOFs) precursors and followed by etching the carbonization product (Cu@Cu-N-C) along with re-annealing treatment. Such hierarchical porous Cu-N-C NDs possess high specific surface area (293 m2 g-1 ) and more exposed Cu single-atom sites, different from their counterparts (Cu@Cu-N-C) and pure N-C control catalysts. Electrochemical tests in alkaline media reveal that they can efficiently catalyze ORR with a half-wave potential of 0.85 V (vs reversible hydrogen electrode), comparable to Pt/C and outperforming Cu@Cu-N-C, N-C, Cu-TPyP-MOFs, and most other reported M-N-C catalysts. Moreover, their stability and methanol-tolerant capability exceed Pt/C. This work may shed some light on optimizing 2D M-N-C nanostructures through bio-inspired pore structure engineering, and accelerate their applications in fuel cells, artificial photosynthesis, or other advanced technological fields.

Investigation of switching behavior of acceptor-doped ferroelectric ceramics

Switching behavior is a general feature in ferroelectrics. The related fatigue effects influenced by defect dipoles in ferroelectrics are still controversial that is focused on the positive and negative effects of oxygen vacancies. Here, we report the polarization switching behavior of acceptor-doped ceramics using the first-order reversal curve (FORC) approach, especially for the abnormal self-rejuvenation effect and the enhanced fatigue endurance in acceptor-doped ceramics. The reversible and irreversible components under electric field in the ceramics were distinguished by the FORC distribution of ideal “hysteron”. The abnormal self-rejuvenation behavior stemmed from dispersive response of hysteron for undoped samples while from the redistribution of defect dipoles for acceptor-doped samples. The self-rejuvenation was induced mainly by the irreversible component. For the fatigue effect, the pinning of domain walls was not the main reason. The re-annealing treatment for a fatigued sample weakened the interactions between the spontaneous polarizations and defect dipoles, but enhanced the dispersion of coercive field. The enhancement of fatigue endurance came from the phase stability of structure in acceptor-doped ceramics, while complex phase evolution existed in undoped ceramic with weak fatigue endurance. Our study shed new light on the interactions between spontaneous polarization and defect dipoles under repetitive AC electric field.

Investigation of Switching Behavior of Acceptor-Doped Ferroelectric Ceramics

Switching behavior is a general feature in ferroelectrics. The related fatigue effects influenced by defect dipoles in ferroelectrics are still controversial that is focused on the positive and negative effect of oxygen vacancies. Here, we report the polarization switching behavior of acceptor-doped ceramics using the first-order reversal curve (FORC) approach, especially for the abnormal self-rejuvenation effect and the enhanced fatigue endurance in acceptor-doped ceramics. The reversible and irreversible components under electric field in the ceramics were distinguished by the FORC distribution of ideal “hysteron”. The abnormal self-rejuvenation behavior stemmed from dispersed response of hysteron for undoped samples while from the redistribution of defect dipoles for acceptor-doped samples. The self-rejuvenation was induced only by the irreversible component. For the fatigue effect, the pinning of domain walls was not the main reason. The re-annealing treatment for a fatigued sample weakened the interactions between the spontaneous polarizations and the defect dipoles, but enhanced the dispersion of coercive field. The structure decomposition was another reason for fatigue effect. The enhancement of fatigue endurance comes from the phase stability of structure in acceptor-doped ceramics, while complex phase evolution exists in undoped ceramic with weak fatigue endurance. Our study shed new light on the interactions between spontaneous polarization and defect dipoles under repetitive AC electric field.

A BiVO4 film photoanode with re-annealing treatment and 2D thin Ti3C2TX flakes decoration for enhanced photoelectrochemical water oxidation

Bismuth vanadate (BiVO4) has been envisioned as a promising photoanode material for photoelectrochemical (PEC) water oxidation. However, the PEC performance of BiVO4 based photoanodes is usually dragged down by the poor charge transport and slow kinetics for an oxygen evolution reaction (OER). Here, a novel composite photoanode of Ti3C2TX/BiVO4 was fabricated for the first time by spin coating thin Ti3C2TX (MXene) flakes onto the surface of a BiVO4 film grown on the FTO substrate. A facile re-annealing treatment of bare BiVO4/FTO photoanode in argon can impressively boost the photocurrent density from 2.1 mA cm−2 up to 2.95 mA cm−2. Experimentally, we clearly elucidated that by re-annealing, the interfacial (BiVO4/FTO) charge recombination could be effectively suppressed due to the better contact between the BiVO4 film and FTO. The coating of thin Ti3C2TX flakes onto the BiVO4 film would further increase the photocurrent density to 3.45 mA cm−2 (measured at 1.23 V vs. reversible hydrogen electrode (RHE) under 1 sun illumination), exhibiting a photoconversion efficiency of 0.78% and a surface charge separation efficiency of 73%. The outstanding PEC performance can be mainly ascribed to the coating of the thin Ti3C2TX (MXene) flakes which function as co-catalysts, facilitating the charge transfer of the photogenerated carriers and reducing the charge recombination on the BiVO4 surface. Our findings provide a facile re-annealing strategy and a novel two-dimensional (2D) material of Ti3C2TX (MXene) as co-catalysts to improve the performance of the BiVO4 photoanode for PEC water oxidation.

The enhancement on thermoluminescence response of rare earth metal-doped CaSO4/CaF2-based thermoluminescence dosimetry driven by polytetrafluoroethylene decomposition

The effect of polytetrafluoroethylene (PTFE) addition and re-annealing treatment to thermoluminescence dosimeter (TLD) material such as CaSO4:RE (rare earth dysprosium (Dy) or thulium (Tm)) was studied at different re-annealing temperatures. The x-ray diffraction pattern showed that CaF2 phase was observed together with CaSO4:Dy at 500 °C, indicating a formation of CaSO4/CaF2:RE composite due to the reaction between CaSO4 and PTFE. Above 600 °C, the CaF2 phase become stronger than that of CaSO4 phase. The thermoluminescence (TL) peak of the composite was shifting from around 180 °C to around 140 °C as the re-annealing temperature increased from 600 to 800 °C, which correspond to TL characteristic of CaSO4 and CaF2 respectively. However, the maximum TL intensity occurred at re-annealing temperature of 700 °C. The results in this study indicate that the sensitivity of CaSO4/CaF2:RE TL response can be improved by controlling the crystallinity of the material as well as the ratio of CaSO4 and CaF2 in the composite.

PTFE Additive and Re-annealing Effect on Thermoluminescence Response of CaSO4:Dy Derived from Co-precipitation Method

Effect of re-annealing treatment in thermoluminescence response of thermoluminescent dosimeter (TLD) CaSO4:Dy and CaSO4:Dy with PTFE (Polytetrafluoroethylene) addition was investigated. CaSO4:Dy was prepared by a co-precipitation method. The PTFE was added before re-annealing treatment which the mass ratio of CaSO4:Dy and PTFE was fixed to 2:3. The re-annealing treatments of the samples were done at temperature 700 °C for 1 hr. The obtained samples were characterized using a Fourier-transform infrared (FTIR) and X-ray diffraction (XRD) to observe the molecule bonding in sample and crystal properties, respectively. From the experimental results, it was observed that the thermoluminescence intensity of CaSO4:Dy, CaSO4:Dy re-annealed at 700 °C, and CaSO4:Dy + PTFE re-annealed at 700 °C are 57.03, 75.15, and 1191.11 nC, respectively. The intensity of 700 °C-re-annealed CaSO4:Dy increased significantly after PTFE addition.

Influence of Magnetic Field Annealing Methods on Soft Magnetic Properties for FeCo-Based Nanocrystalline Alloys

Soft magnetic alloys have been widely applied to modern technology devices, such as transformer cores, choke coils and inductive devices. Magnetic field annealing can induce an uniaxial magnetic anisotropy K u [1-4] so as to improve the soft magnetic properties of alloys for the purpose of coping with different application requirements. So far, FeCo-based nanocrystalline alloys have been explored increasingly in order to improve the magnetic softness at higher temperatures[5-6]. Furthermore, the effect of magnetic field annealing on FeCo-based alloys is more pronounced compared with that of single ferromagnetic element composition [7-8]. Therefore, to explore the optimal magnetic field annealing method of FeCo-based alloys can effectively improve their soft magnetic properties to adapt to more strict application requirements at high temperature conditions. Magnetic field annealing of nanocrystalline alloy mainly includes three methods [9-11]. (a) The direct magnetic field annealing above the crystallization temperature of initial crystalline phase T x1 (magnetic field nanocrystallization). (b) Annealing above T x1 for nanocrystallization without magnetic field and then longitudinal magnetic field annealing below the Curie temperature of amorphous phase T c am. (c) After nonmagnetic field annealing above T x1 followed a magnetic field rean-nealing treatment under the same annealing condition. In order to achieve more superior magnetic softness of FeCo-based nanocrystalline alloys, the soft magnetic properties of nanocrystalline (Fe 1−x Co x ) 73.5 Si 13.5 B 9 Nb 3 Cu 1 (x=0.25,0.5,0.75) alloys under different magnetic field annealing were investigated.

Study of ferroelectric switching and fatigue behaviors in poly(vinylidene fluoride-trifluoroethylene) copolymer nano-films

The nano-films of poly (vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) copolymer, with mole ratio of VDFTrFE 70/30, are deposited on titanium-metallized silicon wafer by spin coating technique. Annealing temperature and humidity dependence of polarization switching and fatigue babivors in ferroelectric P(VDF-TrFE) copolymer thin film capacitors have been investigated. Firstly, the effect of different annealing temperature on polarization behavior is revealed. It is found that the polarization of the film is improved by increasing annealing temperatures. When the annealing temperature is higher than 100℃, with increasing switching cycles, the ferroelectric polarization characteristics exhibit a trend of increasing firstly and then decreasing, a top value appears at the number of cycles near 104. A more appropriate heat treatment temperature is 130℃. Further analyses on the crystalline structures with X-ray diffraction show that the degree of crystallinity of the films is strongly dependent on the annealing temperature. It can be seen that the diffraction peak of the ferroelectric phase ( phase) becomes very strong and sharp with increasing annealing temperatre. It is demonstrated that the effect of annealing temperature on ferroelectric properties could be explained by the changes of the degree of crystallinity in these films from the results of X-ray and the polarization behaviors. Meanwhile, the microstructure of the 140 nm film annealed at 130℃ is obtained by using scanning electron microscope, which shows that the film exhibits a worm-like, dense, well-crystallized microstructure. Secondly, for the capacitor P(VDF-TrFE) films with a thickness of 140 nm, the ferroelectric polarization hysteresis loops as functions of electric field for the films at different relative humidities are achieved. It is obvious that the polarization properties depend on the relative humidity during the film preparation process, the polarizaiton fatigue can be further enhanced through a higher relative humidity during the sample preparation. In addition, one of the most important features for ferroelectric material to be used as an alternative FeRAM is the low leakage current density. Therefore, the descriptions of the leakage current density versus different relative humidities are given. It is observed that the voltage behavior of the leakage current has a minor dependence on relative humidity. In a word, these results illustrate that the polarization properties are strongly dependent not only on the annealing temperature, but also the relative humidity in a process for the preparation of the nano-films. Furthermore, according to a re-annealing treatment to improve the crystalline degree of the ferroelectric phase, the influence of the re-annealing process on the fatigue properties of the films is also studied. The polarization fatigue can be improved obviously by a re-annealing process, and the possible origins have been discussed. To further understand the variation of crystallization properties of the samples before and after re-annealing, the crystallinity of the film are studied by the technique of Fourier transform infrared spectroscopy. It is indicated that the crystallinity of the films can partly be recovered through re-annealing treatment. These results are very helpful and provide an available way to improve the ferroelectric polarization and fatigue properties of the ferroelectric nano-films.

원자력발전소용 316 스테인리스강 배관의 부식특성에 미치는 유도가열벤딩공정의 영향

Recently, the application of bending products has been increased since the industries such as automobile, aerospace, ships, and plants greatly need the usage of pipes. For facility fabrication, bending process is one of key technologies for pipings. Induction heat bending process is composed of bending deformation by repeated local heat and cooling. Because of local heating and compressive strain, detrimental phases may be precipitated and microstructural change can be induced. This work focused on the effect of induction heat bending process on the properties of ASME SA312 TP316 stainless steel. Evaluation was done on the base metal and the bended areas before and after heat treatment. Microstructure analysis, intergranular corrosion test including Huey test, double loop electropotentiokinetic reactivation test, oxalic acid etch test, and anodic polarization test were performed. On the base of microstructural analysis, grain boundaries in bended extrados area were zagged by bending process, but there were no precipitates in grain and grain boundary and the intergranular corrosion rate was similar to that of base metal. However, pitting potentials of bended area were lower than that of the base metal and zagged boundaries was one of the pitting initiation sites. By re-annealing treatment, grain boundary was recovered and pitting potential was similar to that of the base metal.

Dielectric Properties of Nanograined BaTiO&lt;sub&gt;3&lt;/sub&gt; Ceramics Fabricated by Aerosol Deposition Method

Freestanding BaTiO3 ceramics films were fabricated using the aerosol deposition (AD) method and the size effect of nanograined BaTiO3 ceramics was demonstrated. Dense BaTiO3 thick film fabricated by the AD method was crystallized and detached from substrate by an annealing treatment at 600 °C, and then the grain size was controlled by a reannealing treatment at various temperatures. As a result, freestanding BaTiO3 thick films with various grain sizes from 24 to 170 nm were successfully obtained. Polarization–electric field (P–E) measurement revealed that BaTiO3 ceramics with grain sizes of more than 58 nm showed ferroelectricity, whereas BaTiO3 ceramics with an average grain size of 24 nm showed paraelectricity at room temperature. Dielectric measurement indicated that the permittivity decreased with decreasing grain size in the range of 170 to 24 nm.

Temperature dependence of coercive field and fatigue in poly(vinylidene fluoride-trifluoroethylene) copolymer ultra-thin films

The experimental intrinsic coercive field of ferroelectric poly(vinylidene fluoride-trifluoethylene) copolymer films, with both bottom and top gold electrodes is measured at a wide temperature range. In the lower temperature region from −20 to 25 °C, the temperature dependence of coercive field shows good agreement with the prediction by the Landau–Ginzburg (LG) mean-field theory. In the higher temperature region from 25 to 80 °C, the coercive field shows a slow decrease with the increased temperature, where the LG theory is not applicable any more. The temperature-dependent changes in the polymer chains have been analysed. A reversible ‘inherent fatigue’ is observed from the partially recovered remanent polarization after re-annealing a fatigued P(VDF-TrFE) film. FTIR spectra indicate that the interchain spacing does not change from 10 to 107 switching cycles while the degree of all-trans ferroelectric phase decreases gradually with applied switching cycles. After a re-annealing treatment, ferroelectric phase recovers and dipoles at the boundary of crystallites acquire much higher energy.

Electrochemical characteristics of LiNi 0.5Mn 1.5O 4 prepared by spray drying and post-annealing

LiNi 0.5Mn 1.5O 4 was prepared by a spray drying and post-annealing process. The re-annealing treatment in O 2 could not only decrease the Mn 3+ content, but also increased the reversible capacity and significantly improve the rate capability compared to the untreated material. Moreover, the cyclic performance of the LiNi 0.5Mn 1.5O 4 depends on both the cycling rate and operating temperature, which was ascribed to the difference between the phase transition rates between cubic I ↔ cubic II and cubic II ↔ cubic III.

Effect of reannealing treatment in alternating electric field on residual strain in sol–gel derived Pb(Zr,Ti)O3 film

Highly (100)-oriented Pb(Zr,Ti)O3 film was prepared on Pt/Ti/SiO2/Si by sol–gel route. An alternating electric field normal to the film surface was in situ applied to the as-crystallized Pb(Zr,Ti)O3 film during the reannealing treatment, and its effect on the residual strain of the film was investigated by X-ray diffraction. X-ray diffraction measurement shows that the reannealing treatment in alternating electric field has an obvious influence on the reduction of residual strain in the Pb(Zr,Ti)O3 film and platinized silicon substrate. With increase of reannealing treatment temperature in alternating electric field, the reduction of strain in the film increases.

Solid‐Phase Epitaxial Crystallization of Amorphous Ge on Si

Heteroepitaxial Ge films have been obtained by solid‐phase crystallization of amorphous Ge deposited on single crystal <100>Si substrates. The Si substrates were chemically cleaned by conventional procedures without any attempt to achieve atomically clean surfaces. Epitaxial crystallization of the amorphous Ge films were accomplished by furnace annealing at temperatures of 500°–900°C. The as‐crystallized Ge films contain dislocations and twins whose densities decrease with increasing annealing temperature. Significant reduction in twin density has been achieved by using an ion implantation and reannealing treatment. Epitaxial layers of good crystal quality have been grown by chemical vapor deposition on heteroepitaxial Ge films subjected to this treatment.

Solid-phase heteroepitaxy of Ge on 〈100〉Si

Heteroepitaxial Ge films have been obtained by solid-phase crystallization of amorphous Ge deposited on single-crystal 〈100〉Si substrates. The substrates were chemically cleaned by conventional procedures without any attempt to achieve atomically clean surfaces. The as-crystallized Ge films contain dislocations and twins. Reduction in twin density has been achieved by using an ion implantation and reannealing treatment. Epitaxial GaAs layers of good crystal quality have been grown by chemical vapor deposition on heteroepitaxial Ge films subjected to this treatment.