Thickness Of Transition Layer Research Articles

Microstructure and mechanical properties of CP780 steel - 7075 aluminum alloy laser welded joint assisted by rotating magnetic field

Abstract This study uses a rotating magnetic field for laser welding on 1 mm thick CP780 high-strength steel and 1.5 mm thick 7075 aluminum alloy. The effects of different welding parameters (B = 0 mT, B = 65 mT with V = 0°/s, B = 65 mT with V = 10°/s) on the morphology, microstructure, and tensile properties of welded joints are analyzed. At B = 0 mT, the weld shape is V-shaped, with the intermetallic compounds primarily consisting of needle-like brittle Al-rich (Fe, Si)Al2 phase and fewer granular ductile Fe-rich (Fe, Si)Al phase, resulting in poor mechanical properties. With the application of the rotating magnetic field, the laser energy becomes more concentrated, forming a ‘T’ shape weld. The rotating magnetic field (B = 65 mT with V = 10°/s) generates a constantly changing Lorentz force, promoting molten pool flow and enhancing Fe diffusion within the weld. This process reduces needle-like brittle Al-rich (Fe, Si)Al2 phase and increases granular ductile Fe-rich (Fe, Si)Al phase. It also accelerates the weld cooling rate and inhibits the reaction time and grain growth of intermetallic compounds, thereby reducing the thickness and content of the intermediate transition layer and significantly improving mechanical properties. A comprehensive comparison shows that the best mechanical properties are achieved at B = 65 mT with V = 10°/s. This study offers new insights and a theoretical foundation for achieving cost-effective, high-performance welded joints in advanced high-strength steel and high-strength aluminum alloy for automobiles, thereby facilitating lightweight vehicle development.

Enhancing acid corrosion resistance in alkaline-activated materials with water treatment residue and blast-furnace slag

This study investigates the acid corrosion resistance of an alkaline-activated material (AAM) composed of ground granulated blast-furnace slag (GGBFS) and water treatment residue (WTR) as precursors. WTR, a byproduct of the drinking water treatment process rich in aluminium and silicon, proves to be a suitable precursor for AAM after cost-effective pre-treatment involving calcination and grinding. As its low-Ca content and aluminosilicate nature of the treated WTR, the AAM incorporating WTR exhibits significant potential for improving acid resistance. This is attributed to the formation of less acid-reactive N-A-S-H gels than C-A-S-H gels in high-Ca AAMs, indicating its applicability in concrete sewage pipes where microbiologically generated acid corrosion is prevalent. In the paper, a comprehensive analysis, including mechanical performance, ion leaching behaviour, and microstructural characteristics, was conducted on mortar samples containing varying WTR/GGBFS ratios before and after exposure to sulfuric acid. Incorporating WTR up to 40 % effectively reduced acid-induced strength loss compared to neat-GGBFS AAM. The obtained results reveal that high-Ca AAMs facilitate gypsum formation during acid attack, leading to mechanical degradation. The inclusion of WTR induces a Si-rich transition layer between the corroded and intact matrix, mitigating sulfate diffusion. The release of aluminium from WTR promotes secondary precipitation of aluminosilicate, beneficially increasing the thickness of the transition layer. This thicker transition layer in the higher WTR samples is advantageous in reducing the likelihood of cracks and reducing the sulfate transportation into the intact matrix.

A mechanical TiAl/TiAlN multinanolayer coating model based on microstructural analysis and nanoindentation

A finite element model reproducing the mechanical behaviour during nanoindentation tests on Ti0.67Al0.33/Ti0.54Al0.46N multilayer coatings was developed. Coatings with two different nanoperiods (10 and 50 nm) were deposited by radio-frequency magnetron sputtering from a single sintered titanium/aluminium target using the reactive gas pulsing process. X-ray diffraction and transmission electron microscopy confirmed the multilayer stacking of the coatings. The finite element models of coatings with these two stacking periods were built considering successive hypotheses: equal thicknesses for metal and nitride nanolayers stacked without transition layer, equal thicknesses stacking with a transition layer between each metal and nitride nanolayer and finally imbalanced thicknesses stacking with a transition layer. The elastic and plastic properties of the stacked nanolayers were determined on thick monolithic coatings of metal and nitride using indentation testing and the finite element model updating method respectively. The elastic-plastic properties of the interface were introduced in the multilayer model as a rule of mixtures of the metal and nitride properties using two hypotheses: parallel or serial. For 50 nm-period film, the interface has a negligible effect on the overall indentation response. On the other hand, for the 10 nm period, the imbalanced stacking model with precise knowledge of the transition layer thickness obtained by N K-edge electron energy loss spectroscopy is required to reproduce the experimental indentation curve. Compared to classical analytical models accounting for hardness, not only the hardnesses but also the indentation moduli appear to be well predicted and evaluated in this work.

Microstructure and mechanical properties of Mg/Al laminated composite: The effect of transition layer thickness

This study successfully prepared Mg/Al laminated composites with various thicknesses of pure Cu transition layer via extrusion, overcoming the challenge of forming of Mg/Al composite plates through stacked extrusion technology. The effects of varying Cu layer thicknesses on the microstructure, mechanical properties, and fracture behaviors were systematically investigated. Microstructure analysis showed an uneven Cu layer distribution at the interface of the composite plate, characterized by alternating thicker and thinner layers, which stemmed from the low fluidity of pure Cu during extrusion. Although the thicker Cu layer significantly inhibited the diffusion of Mg and Al elements, there was still a significant enrichment of Mg-Al intermetallic compounds (IMCs) in the thinner Cu layer. There hard and brittle IMCs caused cracking during the deformation process. Increasing Cu layer thickness did not significantly affect the microstructure but contributed to the decrease of strength owing to increased stress concentration. Moreover, the thicker Cu layer exacerbated its uneven distribution and Mg-Al IMCs enrichment at the interface, resulting in a pattern of first decreasing and then increasing elongation and shear strength of the laminated composite.

Enhance the tribological performance of soft AISI 1045 steel through a CrN/W-DLC/DLC multilayer coating

Special equipment vehicles typically operate in complex environments, leading to wear and failure of the chassis's rotary seal shaft predominantly made of soft AISI 1045 steel. An effective approach to prolong the service life is to apply a hard coating on the working surface. Previous research have primarily concentrated on the coating for hard high-speed steel. However, the significant disparity in physical characteristics between soft AISI 1045 steel and the hard coating results in a weak interface adhesion. This study produces a CrN/W-DLC/DLC multilayer coating on the soft AISI 1045 steel with strong interfacial adhesion and superior friction and wear property through modulation of the CrN transition layer thickness. The multilayer coating consists of five layers, a CrN transition layer, a Cr layer, a Cr/WC alternating layer, a W-DLC/DLC alternating layer, and the topmost DLC layer. The thickest CrN interlayer coating achieves the Lc2 and Lc3 value of 13.9 ± 0.2 N and 20.4 ± 0.9 N. The optimized CrN/W-DLC/DLC coating reduces the internal stress of the DLC coating and enhances its adhesion. Importantly, the average friction coefficient and wear cross-sectional area of the CrN/W-DLC/DLC multilayer coatings decrease accordingly. The thickest CrN interlayer coating exhibits superior outstanding wear resistance evidenced by an average friction coefficient of 0.119, a steady-state friction coefficient of 0.097 and a wear volume of 1.508 × 106 μm3. The presence of a high proportion of sp2 bonds in the thickest CrN interlayer coating, which are susceptible to graphitization, along with a thicker transition layer that enhances the coating's support, leads to narrower wear traces. The primary wear mechanisms observed in the friction and wear test of CrN/W-DLC/DLC coatings are oxidative wear and tribo-abrasive wear. The work provides a significant promise for application in vehicle rotary seal components and a theoretical reference for enhancing the wear resistance of the seal surface.

Microstructure, mechanical and corrosion behavior of CrNx/Al2O3 multilayer films deposited by magnetron sputtering

A novel design was adopted to improve corrosion resistance of 2024 Al alloys by magnetron sputtering CrNx based multilayer films with Al2O3 intercalation. The multilayer films were composed of inhomogeneous structure, i.e., thick CrNx transition layer (∼2 μm) + CrNx/Al2O3 multilayer (∼1 μm). The effect of Al2O3 interlayer and modulation period on microstructure and performance of multilayer films were investigated. The nitride layer was dominated by Cr2N and CrN with minor Cr, while the Al2O3 layer displayed in the amorphous form. The intercalation of Al2O3 blocked the columnar growth in CrNx layers and refined the grains. As the period increased, the cluster particle size decreased and the mechanical properties increased, with the maximum hardness and modulus at CN-8 (19.13 GPa and 282.2 GPa). In addition, the multilayer structure enhanced the bonding between the film and the substrate, and has an improvement on the hard and brittle properties of the film. The multilayer films showed improved corrosion resistance than the CrNx mono-layer in 3.5 wt% NaCl solution. The film with CrNx-top layer showed superior corrosion resistance than the film with Al2O3-top layer. The increasing period also enhanced corrosion resistance, showing an excellent corrosion potential and corrosion current density (Ecorr=-0.538 V, icorr=0.96 μA·cm−2) at CN-8.

The Allen–Cahn model with a time-dependent parameter for motion by mean curvature up to the singularity

In this article, we investigate the temporal evolution of arbitrary, simple, closed two-dimensional (2D) and three-dimensional (3D) interfaces under motion driven by mean curvature up to a singularity. To facilitate this investigation, we propose a novel Allen–Cahn (AC) model with a time-dependent interfacial thickness parameter. The original AC equation was developed to model the phase separation of a binary mixture. It is well known that a level set or interface of the solution of the AC equation obeys the dynamics of motion by curvature as the interfacial thickness parameter approaches zero. Generally, it is difficult to find a closed-form analytic solution of the AC equation with any initial condition. Therefore, we need to estimate the solution of the AC equation through computational approaches such as finite difference method (FDM), finite element method (FEM), Fourier-spectral method (FSM), and finite volume method (FVM). Any simple, closed curves and convex surfaces eventually shrink to a point due to motion by mean curvature. Therefore, it becomes necessary to use adaptive mesh techniques to resolve this small size problem. However, even though we use adaptive mesh techniques, we still confront the relatively thick interfacial transition layer when the curves or interfaces become very small. To avoid this problem, we can start with a very small mesh size for a small value of the interfacial parameter, which results in an extremely high computational cost even when using adaptive mesh techniques. To resolve these issues, we present the AC equation with a time-dependent interfacial parameter and develop an adaptive mesh refinement system. To show the superior performance of the proposed mathematical equation and its computational algorithm, we present various numerical experiments and investigate the motion by mean curvature up to the singularity of curves in 2D space and interfaces in 3D space.

In situ preparation of SnO2/Pd@TiO2 bilayer sensor for highly sensitive and fast detection of H2S based on electrohydrodynamic jet printing

A micron-scale bilayer H2S sensor fabricated by electrohydrodynamic (EHD) jet printing in situ was evaluated. The prepared sensor consisted of a Pd@TiO2 cover layer (porous catalytic sensing layer), a SnO2 bottom layer (electron transport layer) and a Sn-Ti transition layer between them. The addition of TiO2 nanoparticles to the cover layer led to a porous structure after one-step sintering. The increase in specific surface area and the formation of heterojunction effectively improved the sensor sensitivity. The PdO nanoparticles loaded on the surface of TiO2 nanoparticles further improved the performance due to its catalysis. Since the kinetic energy of droplets of the same size generated by EHD inkjet printing is about 48 times that of inkjet printing, the film density is much higher than that of inkjet printing. The relatively dense bottom layer, and the thick and stable transition layer improved the long-term stability of the sensor. The detection limit of the sensor is 6 ppb, with linear range of 0.02–10 ppm H2S. The response and recovery times are 7 s and 45 s (2 ppm H2S), respectively. After 9 months of intermittent measurement, the response of the sensor to 2 ppm H2S decreased by only 10.6%.

Transforming WLP Applications: Introducing Cutting-Edge Next-Generation Nanotwinned Copper Processes to Revolutionize Hybrid Bonding

We discuss two electrochemical plating approaches for nanotwinned copper (ECP nt-Cu) - Gen 1 and Gen 2. These two approaches allow control over columnar width and transition layer thickness on Cu substrates, enabling the filling of nanotwinned Cu for bonding applications. Both approaches produce stable nt-Cu structures with minimal transition layers when electroplated on (111) Cu substrate. However, grain size, transition layer thickness on polycrystalline substrates and feature-filling behavior differ. The researchers suggest that the choice between Gen 1 and Gen 2 depends on the feature size, aspect ratio and applications. In addition, further exploration into other additives may improve bottom-up filling capabilities, enabling more versatility for applications. Both approaches enable the filling of nanotwinned Cu inside bottom-seeded and complete-seeded features, with 100% nanotwin growth parallel to the substrate for bottom-seeded features. However, nanotwin growth percentage and direction depend on feature aspect ratio and size for complete-seeded features. Gen 2 tends to have less sidewall growth due to its smaller grain size and is more compatible with other additivies, making it promising for high aspect ratio small features.

The mechanical property and microstructural thermal stability of gradient-microstructured nanotwinned copper films electrodeposited on the highly (111)-orientated substrates

Three different substrates with varying (111) textures were used to study the epitaxial growth behavior of nanotwinned copper (nt-Cu) films during direct current electroplating. The (111) proportions for substrates are 78.5%, 97.5%, and 100%, while for the electrodeposits they are 69.3%, 92.7%, and 98.3%, showing a positive correlation between the (111) proportions of the substrates and the electrodeposits. Secondary ion microscopy (SIM) reveals a transition layer consisting of fine grains forms between the columnar nanotwinned grains region and the substrate, exhibiting a gradient microstructure within the nt-Cu films. The thickness of the transition layer shows a reducing tendency as the (111) proportion of substrate increases. Furthermore, to investigate the mechanical properties of the transition layer, a nano-indentation test was performed on the cross-section of gradient-microstructured films. The average hardness of the transition layer near the substrate is 3–4 GPa, which is approximately two times higher than that of the columnar nanotwinned region. The excellent hardness is probably induced by the decrease in grain size and the presence of high-density twin boundaries within the grains. An in-situ annealing test at 300 °C was performed on these three electrodeposits to assess their microstructural thermal stability. It is noticed that the thickness of transition layer would affect the competition of grain growth between substrate grains and columnar nanotwinned grains during aging. Higher microstructural thermal stability could be achieved with fewer grains in the transition layer. Overall, this study reveals the high mechanical properties and microstructural thermal stability of the transition layer, which should be helpful in understanding and promoting the application of nt-Cu thin films.

Transforming WLP Applications: Introducing Cutting-Edge Next-Generation Nanotwinned Copper Processes to Revolutionize Hybrid Bonding

We discuss two electrochemical plating approaches for nanotwinned copper (ECP nt-Cu)—Gen 1 and Gen 2. These two approaches allow control over columnar width and transition layer thickness on Cu substrates, enabling the filling of nanotwinned Cu for bonding applications. Both approaches produce stable nt-Cu structures with minimal transition layers when electroplated on (111) Cu substrate. However, grain size, transition layer thickness on polycrystalline substrates, and feature-filling behavior differ. The researchers suggest that the choice between Gen 1 and Gen 2 depends on the feature size, aspect ratio, and applications. In addition, further exploration into other additives improves bottom-up filling capabilities, enabling more versatility for applications. Both approaches enable the filling of nanotwinned Cu inside bottom-seeded and complete-seeded features, with 100% nanotwin growth parallel to the substrate for bottomseeded features. However, nanotwin growth percentage and direction depend on feature size and aspect ratio for complete-seeded features. Gen 2 tends to have less sidewall growth due to its smaller grain size and is more compatible with other additives, making it promising for high aspect ratio small features.

Effect of layer thickness for the bounce of a particle settling through a density transition layer.

We study numerically a spherical particle settling through a density transition layer at moderate Reynolds numbers Re_{u}=69∼259 for the upper fluid. We investigate how the transition layer thickness affects the particle's bouncing behavior as it crosses the interface. The previous intuitive understanding was that the bounce occurs when the relative thickness of the transition layer, L/D, which is characterized by the ratio of the layer thickness L to the particle diameter D, is small. Indeed, we report no bounce phenomenon for very thick interfaces, i.e., L/D>10 in the current parametric range. However, we argue that the bounce can also be inhibited when L/D is too small. Upon a fixed upper layer Reynolds number Re_{u}=207 with varying L/D, we examine the flow evolution of these cases. We propose that this inhibition is attributed to two mechanisms. First, as the interface thickness decreases, the detachment of the attached lighter fluid from the upper layer occurs more rapidly, resulting in a faster decrease in buoyancy. Second, in the case of a very thin interface (L/D=0.5-3.0), the residual light fluid accumulates and undergoes a secondary detachment, separating from the particle at an angle relative to the central axis. This secondary detachment reduces the drag force and effectively prevents the particle from experiencing a rebound motion.

Modulating microstructure and thermal properties of diamond/SiNx/GaN multilayer structure by diamond growth temperature

Numerous growth conditions affect thermal properties in diamond/SiNx/GaN multilayer structures, where diamond growth temperature is an important parameter and has not been adequately studied in the past. This article studies the relationship between the microstructure and thermal properties of diamond/SiNx/GaN multilayer structures under different diamond growth temperatures (740 °C–860 °C). The thermal boundary resistance of the diamond/GaN (TBReff, Dia/GaN) and thermal conductivity of the diamond (kDiamond) are measured using transient thermoreflectance (TTR). The lowest TBReff, Dia/GaN and highest kDiamond are achieved simultaneously at a growth temperature of 800 °C, and the difference in TBReff, Dia/GaN and kDiamond at different temperatures is up to 3–4 times. At the low growth temperature (740 °C), the thick transition layer is formed due to the insufficient ability of etching amorphous carbon and a significant carbon diffusion, resulting in significantly increased TBReff, Dia/GaN. At the high growth temperature (860 °C), the lattice distortion of GaN at the interface and the graphite phase in the transition layer contributed to the increase of TBReff, Dia/GaN. The thin diamond layer thickness and secondary nucleation result in low kDiamond except for 800 °C. The device simulation using the experimental kDiamond and TBReff, Dia/GaN at 800 °C predicts a 23 % reduction in maximum device temperature (Tmax) when the surface of GaN HEMTs is grown with a thin diamond layer.

Improved passivation effect of additively manufactured WE43 porous scaffolds treated by high temperature oxidation in pure oxygen atmosphere

WE43 is a well-recognized magnesium alloy and has been successfully used in clinical biodegradable implants. High temperature oxidation (HTO) has been developed to inhibit fast degradation of WE43 alloy fabricated by laser powder bed fusion (L-PBF). This study involves constructing WE43 porous scaffolds via L-PBF, followed by HTO treatment using air (abbreviated as HTO-A) and pure oxygen (abbreviated as HTO-O) respectively. Electrochemical and immersion tests are performed to evaluate the oxidizing atmosphere’s influence on degradation. Compared with HTO-A, HTO-O achieves a denser and more continuous oxide layer and a thicker transition layer. The weight loss of HTO-O scaffold was 20.13 % after 14 days of immersion in Hank's solution, which was much lower than that of HTO-A scaffold (53.70 %), indicating that undergoing HTO treatment in pure oxygen markedly enhances the scaffold's corrosion resistance.

Length-scale effect on the hardness of metallic/ceramic multilayered composites: A machine learning prediction

The length-scale effect on the hardness of Al/Si3N4 multilayered composites were investigated via combined experimental and machine learning approaches. It was found that the hardness decreases with increase of the individual layer thickness, in agreement with the classic Hall-Petch relation. However, the hardness decrease became moderate when the individual layer thickness was less than 80 nm. The individual critical layer thickness of metallic/ceramic multilayered composites for the change in deformation mechanism was obtained by machine learning methods. The prediction results indicated that the individual critical transition layer thickness was mainly determined by the metal layer, and the corresponding critical transition hardness was positively correlated with the elastic modulus of the ceramic layer. Importantly, it was confirmed that the hardness of other metallic/ceramic multilayered composite systems could be predicted by the machine learning approach, especially the optimized random forest regression (RFR) model.

WC-18Co reinforced Iron matrix composites: Microstructure and interface characteristics

Particle reinforced iron matrix composites have gained considerable attention as advanced structural materials. In this study, large-sized WC-18Co reinforced iron matrix composites were prepared using the casting infiltration method. We investigated the microstructure and interface characteristics of WC-18Co/FMC, analyzed the stress state at the interface, and tested the mechanical and tribological properties of the composite material. The research findings reveal that WC-18Co/FMC is a multiphase system composed of WC, M3W3C (M = Fe, Co), and precipitates. The strong interface reaction results in the formation of a thick transition layer between WC-18Co and the matrix. Grain refinement occurs around the reinforcing particles. During solidification, the difference in thermal expansion coefficients between WC-18Co and FMC induces thermal stress, leading to compressive residual stress on both sides of the interface. The compressive stress state inhibits crack initiation and propagation, enhancing the bonding strength. Alternating stresses at the interface enhance dislocation motion, grain slip, and twinning phenomena in the transition layer. Nanoscale compounds embedded in the transition layer impede dislocation slip, resulting in dislocation entanglement and pile-up. WC-18Co/FMC exhibits a 60.66% increase in hardness compared to FMC. Under impact energies of 1 J, 3 J, and 5 J, the wear resistance improves by factors of 2.985, 2.358, and 2.072, respectively. The significant improvement in the composite material's performance is attributed to strengthening mechanisms such as the multiphase system, grain refinement, nanoscale precipitates, and residual stress strengthening.

Effect of bias-enhanced nucleation on the microstructure and thermal boundary resistance of GaN/SiNx/diamond multilayer composites

The low effective thermal boundary resistance (TBReff) at the GaN/diamond interface is very important for the development of high-power, high-frequency and high-temperature GaN-on-diamond devices. The nucleation and growth of diamond are key processes for modulating the TBReff. This work proposed the bias enhanced nucleation technique to adjust the nucleation of GaN/SiNx/diamond multilayer composites in the MPCVD process at different bias voltages (400–700 V), thereby adjusting TBReff. Pulse bias is beneficial to a stable plasma environment and to obtain a complete GaN/diamond interface structure. The transient thermoreflectance characterization indicated that the GaN/SiNx/diamond multilayer composite prepared under 700 V bias nucleation condition had the lowest TBReff (26 ± 10 m2K/GW), whereas the GaN/SiNx/diamond multilayer composite at 600 V bias had the highest TBReff (83 ± 18 m2K/GW). The role of bias enhanced nucleation process in the TBReff was systematically analyzed by electron microscopies (TEM and SEM) and Raman spectroscopy. The GaN/SiNx/diamond multilayer composite prepared at 600 V showed a thick mixed transition layer containing multiphase structures and rough interfaces due to efficient subsurface ion implantation, resulting in high TBReff. In contrast, at 700 V, a thinner nucleation zone and smoother interface result in the lowest TBReff. This work demonstrated the potential of adjusting TBReff at the GaN/diamond interface by using bias enhanced nucleation technique to modulate the diamond nucleation and growth processes.

Synthesizing SiC layer on diamond by heat treatment and its effects on density and thermal conductivity of diamond/W composite

In order to improve the thermal conductivity of W composites as plasma-facing materials, the interface bonding and interfacial thermal resistance of the composites are the key issues to be solved. Based on our previous study, although Si coating on diamond surface can improve the interface bonding and thermal conductivity of the composite, there still existed the interfacial reaction between W and diamond, which produced more low thermal conductivity compounds (WC/W2C) and added the interfacial thermal resistance of the composites. To further improve the interface bonding and increased the thermal conductivity of diamond/W composites, the Si-coated diamonds were used to prepare the Si-SiC dual layer on diamond via vacuum heat treatment and then to fabricate diamond/W composites (HT-coated diamond/W composite). The effects of temperature and holding time of the heat treatment on coating and its interface bonding with the composites were investigated by scanning electron microscopy, X-ray diffraction and transmission electron microscopy. The results showed that a stable and dense Si-SiC-diamond structure was formed after heat treatment at 1200 °C for 1 h, and the thickness of SiC transition layer was about 20 nm. Thermodynamic analysis demonstrated the reaction rate of SiC increased gradually first and then sharply from 1000 °C to 1400 °C. The integrity of the coating on the diamond surface was strongly impacted by residual compressive stress of the SiC layer, and its value increased with the SiC thickness. The Si-SiC dual layer evidently improved the interface bonding and thermal conductivity of diamond/W composite under the combined influence of reaction diffusion at SiC-W interface, inter-diffusion at W-Si interface, and the orientation relationship at diamond-SiC interface. Theoretical thermal analysis proved that HT-coated diamond/W composite possessing lower interface thermal resistance than that of Si-coated diamond/W composite and raw diamond/W composite achieved higher thermal conductivity of 205 W m−1 K−1.

Effect of Al2O3 Transition Layer Thickness on the Microstructure and Ferroelectric Properties of Lead Zirconate Titanate

Effect of Al2O3 Transition Layer Thickness on the Microstructure and Ferroelectric Properties of Lead Zirconate Titanate

Zavisimost' dielektricheskoy pronitsaemosti i elektrokaloricheskogo effekta ot razmera granuly segnetoelektricheskoy keramiki

We consider the problem of determining the permittivity and the electrocaloric effect in the model of a ferroelectric ceramics grain. We assume that a grain consists of a spherical ferroelectric core coated with a dielectric shell and placed into a dielectric matrix. The transition layer thickness is assumed small as compared to the grain size. The dependence of the polarization on the electric field in the core is given by the nonlinear Ginzburg–Landau equation. The polarization reversal is induced by a change in the electric field that is considered uniform at large distance from the grain. The electrostriction effect in the core–shell–matrix three-phase system produces an elastic field described by linear equations. To take into account the effect of domain walls on the physical characteristics of the ceramics in the given model, we propose that the Kittel–Mitsui–Furuichi approach be used. The proposed computational algorithm makes it possible to refine the dependence of the number of domains on the spherical grain size. The electrocaloric effect in the grain is represented by the combination of the primary and secondary effects that appear due to ordering of dipole moments of the ferroelectric with the perovskite structure; by way of example, we consider the barium titanate ceramics. For this material, we report on the results of calculations of the dependences of the permittivity and individual electrocaloric effect components on the grain size.