Core-shell Microstructure Research Articles

Enhanced Thermal Conductivity and Stability of Hydrated Salt Phase Change Microcapsules With GO/SiO2 Hybrid Shell for Battery Thermal Management

AbstractHerein, the synthesis of a novel microencapsulated phase change material via a sol–gel method is presented, featuring disodium hydrogen phosphate dodecahydrate as the core and a SiO2/graphene oxide composite as the shell. The morphology and core–shell microstructure of the synthesized microcapsules are characterized using scanning electron microscopy. The phase change performance and thermal stability are evaluated by differential scanning calorimetry and a high/low temperature test chamber, respectively. Energy dispersive X‐ray spectroscopy and Fourier transform infrared spectroscopy are employed to determine the chemical composition of the microcapsules. The findings reveal that the MEPCM exhibited a high melting enthalpy of 174.3 J g−1. The degree of supercooling is reduced by 2.1 °C, and after 600 thermal cycles, the phase change enthalpy of the microcapsules showed a minor decrease of ≈6.0%. Notably, the thermal conductivity of the microcapsules is significantly enhanced, increasing by up to 51.8%. When integrated into the thermal management systems of lithium‐ion batteries, the MEPCM effectively maintained the battery temperature below 46 °C under a 3 C charging rate. In summary, these results suggest that the hydrated salt microcapsule with its hybrid silica and graphene oxide shell is a promising material for the thermal management of lithium‐ion batteries.

Remarkable energy storage performance of BiFeO3-based high-entropy lead-free ceramics and multilayers

Electrostatic energy storage capacitors featuring fast charge–discharge capability play an indispensable role in pulsed power capacitors. However, the inverse correlation between polarization and dielectric breakdown strength (Eb) is the main obstacle limiting the access to high recoverable energy storage density (Wrec) and high efficiency (η). In this work, we designed a series of novel (1-x)BiFeO3-x(Ba0.2Sr0.2Ca0.2Bi0.2Na0.2)TiO3 (BF-xBSCBNT, x = 0.4–1.0) high-entropy lead-free relaxor ferroelectric ceramics. The synergy of refined grain size, broadened band gap, and core–shell microstructure is well-investigated by experimental results and phase-field simulations. High polarization difference is achieved by the strengthened relaxation behavior and the dominated polar nanoregions (PNRs). Both high Wrec of 6.0 J/cm3 and η of 81.1 % are achieved in the BF–0.8BSCBNT ceramics. In particular, a remarkable Wrec of 12.1 J/cm3 with a η of 86.1 % are obtained in the multilayer ceramic capacitors (MLCCs) fabricated from the x = 0.8 composition. Excellent temperature stability (<4.0 % in the range of 25–140 °C) and frequency stability (<6.2 % in the range of 1–500 Hz) are also achieved in MLCCs. The excellent energy storage performance demonstrates that high-entropy strategy is effective to develop novel lead-fee ceramics and devices for energy storage applications.

Achieving high-performance regeneration of grain boundary diffusion Nd-Fe-B sludge via an ultra-short process

The grinding sludge of grain boundary diffusion Nd-Fe-B magnet is rich in heavy rare earth and has a typical core–shell microstructure. In this work, an ultra-short process was developed to realize green, in-situ regeneration of the sludge and efficient reuse of heavy rare earth elements. The regenerated magnets showed excellent magnetic performance and good temperature stability which were fabricated after the purification of sludge, composition regulation with rare earth-rich compounds, Nd42.1FebalB0.79, NdHx, (PrNd)Hx, and sintering. Especially, the magnet prepared by using Nd42.1FebalB0.79 alloy had significant property recovery, where remanence and coercivity were restored to 12.8 kG, and 20.6 kOe, respectively, reaching 97.7 % and 162.5 % of the original magnet. The magnetization reversal behavior and the coercivity mechanism were analyzed to keep the nucleation mechanism, and the high coercivity stemmed from the repair and optimization of the grain boundary by introducing rare earth-rich alloys, the full utilization of heavy rare earth elements, and the core–shell microstructure rooted in the sludge as well.

Phototactic/Photosynthetic/Magnetic-Powered Chlamydomonas Reinhardtii-Metal-Organic Frameworks Micro/Nanomotors for Intelligent Thrombolytic Management and Ischemia Alleviation.

Thrombosis presents a critical health threat globally, with high mortality and incidence rates. Clinical treatment faces challenges such as low thrombolytic agent bioavailability, thrombosis recurrence, ischemic hypoxia damage, and neural degeneration. This study developed biocompatible Chlamydomonas Reinhardtii micromotors (CHL) with photo/magnetic capabilities to address these needs. These CHL micromotors, equipped with phototaxis and photosynthesis abilities, offer promising solutions. A core aspect of this innovation involves incorporating polysaccharides (glycol chitosan (GCS) and fucoidan (F)) into ferric Metal-organic frameworks (MOFs), loaded with urokinase (UK), and subsequently self-assembled onto the multimodal CHL, forming a core-shell microstructure (CHL@GCS/F-UK-MOF). Under light-navigation, CHL@GCS/F-UK-MOF is shown to penetrate thrombi, enhancing thrombolytic biodistribution. Combining CHL@GCS/F-UK-MOF with the magnetic hyperthermia technique achieves stimuli-responsive multiple-release, accelerating thrombolysis and rapidly restoring blocked blood vessels. Moreover, this approach attenuates thrombi-induced ischemic hypoxia disorder and tissue damage. The photosynthetic and magnetotherapeutic properties of CHL@GCS/F-UK-MOF, along with their protective effects, including reduced apoptosis, enhanced behavioral function, induced Heat Shock Protein (HSP), polarized M2 macrophages, and mitigated hypoxia, are confirmed through biochemical, microscopic, and behavioral assessments. This multifunctional biomimetic platform, integrating photo-magnetic techniques, offers a comprehensive approach to cardiovascular management, advancing related technologies.

Thin thickness electromagnetic wave absorbent: Fe3O4 decorated carbon nanofibers composite with designable 3D hierarchical architecture

Designable 3D hierarchical architecture with multi-component heterostructure has been built to form a connected network by fully utilizing the advantages of one-dimensional carbon nanofibers. Fe3O4 decorated carbon nanofibers, which exhibited core-shell microstructures, were successfully prepared by solvothermal and electrospinning technology. Their electromagnetic wave absorption (EWA) performances were explored. The morphology which determined the electromagnetic (EM) parameters can be controlled by adjusting the mass ratio of the raw material. The Fe3O4 decorated carbon nanofibers composite showed an excellent absorbing capability. At a thickness of 2.5 mm, the minimum reflection loss (RLmin) value was −28.28 dB. In particular, the widest effective absorption bandwidth (EAB) can reach up to 2.96 GHz at 1.5 mm. It was more surprising that the effective absorption (RL ≤ −10 dB) occurred when the thickness was only 1.0 mm. The absorption mechanism study revealed that the connected structure facilitated the formation of conductive networks, leading to conductive loss, multiple reflection and scatterings, and interfacial polarization loss. The defects that created during carbonization process enhanced the dipole polarization. The generated magnetic loss which mainly consisted of natural resonance and exchanged resonance loss enhanced the attenuation of EW. Moreover, good impedance matching resulting from the synergistic effect of composition and unique porous network also played an important role. The little filler loading and the thin thickness make the composite have a high EWA performance, which is promising for EWA applications.

CaTiO3 nanoparticles as functional additives for the BaTiO3-based X8R type dielectric ceramics

This research investigates the potential of Calcium titanate (CaTiO3 or CT) nanoparticles as functional additives to enhance the dielectric properties of Barium titanate (BaTiO3 or BT)-based ceramic dielectrics. To address the need for high-temperature stability in MLCC (multilayer ceramic capacitor) applications, especially within the automotive and aerospace sectors, we have explored BT-based complex perovskite solid solutions comprising various cation substitutions, including Ca2+ and Yb3+, into barium titanate (BT) as a method to suppress the dielectric property anomaly near the Curie temperature effectively. The focus is on the impact of the application of CT nanoparticles as additive materials on phase formation, microstructure development, and dielectric behavior of the resulting ceramics to align with the Extended 'Temperature Coefficient of Capacitance (TCC)' criteria defined by the EIA X8R specification. When the hydrothermally synthesized CT nanopowder was applied in the Ca-doped BT ceramics fabrications as source material of the Ca dopants, it was beneficial to achieve both temperature stability and high dielectric constant. The CT nanoparticles are believed to play multiple roles during the solid-state reaction with BT and rare earth dopant (Yb). Since the Yb3+ ions can be more easily dissolved into the CT lattice than BT with their amphoteric character, the CT nanoparticles in the BT-CT-Yb2O3 mixture can act as an intermediary, dissolving the Yb3+ first in its A- or B-site before the final solid-solution formation with the BT. The sequential substitutions of the Yb3+ and Ca2+ into BT via CT nanoparticles could affect the site occupancy of Ca2+ in the BT lattice, which is very important in determining the dielectric properties of the Ca-doped BT processed in reducing atmospheres. Through a comprehensive experimental approach, including phase composition analysis via X-ray diffraction (XRD) and microstructural examination using Field Emission Scanning Electron Microscopy (FE-SEM) and Transmission Electron Microscopy (TEM), this work reveals the significance of synthetic methodology and dopant incorporation strategy on achieving a desired core-shell microstructure and improved dielectric performance. This research underscores the efficacy of CT nanoparticles as a promising route towards the development of BT-based dielectric ceramics with superior temperature stability, offering valuable insights for the advancement of MLCC technology to cater to high-temperature applications.

A novel strategy to regulate the precipitation-strengthened high-entropy alloy fabricated by laser directed energy deposition

The optimization of the aging process is an effective strategy for achieving excellent performance in the rapidly solidified CoCrFeNiTi0.7 high-entropy alloy (HEA). Current research has clearly demonstrated that the unique design of the high-low duplex aging (HLDA) strategy plays a crucial role in achieving outstanding wear resistance in additive manufacturing of the rapidly solidified CoCrFeNiTi0.7 HEA. The microhardness of the SA-750 and HLDA samples increased to approximately 678 HV and 729 HV, respectively, compared to the as-deposited sample (LDED) with a microhardness of approximately 506 HV. Additionally, the wear rates of the SA-750 and HLDA samples were reduced by approximately 17.1% and 24.7%, respectively, compared to the LDED sample. This remarkable improvement in wear resistance can be attributed to the introduction of high-density nanoscale core-shell microstructures formed by secondary η2 and L12-γ' phases. Furthermore, when compared to the grain size of SA-750 (65.63 μm), the HLDA sample exhibited the precipitation of cellular precipitates at the grain boundary, and the grain size (68.46 μm) did not show significant growth or coarsening. This demonstrates the precise control of the matrix grain size achieved in our study. Therefore, the high-low duplex aging treatment has been validated for developing high-performance rapidly solidified CoCrFeNiTi0.7 HEA. This strategy provides a targeted approach for tissue design to tap into the maximum potential of additive manufacturing precipitation-strengthened HEAs.

Application of Johnson's approximation in finite element modeling for electric field‐dependent materials

AbstractJohnson's approximation is implemented in a finite element code to simulate the electric field dependence of a core–shell microstructure material. We show how the microstructure, based here on a 50:50 volume fraction, influences the measured effective permittivity as a function of applied voltage. Using a Johnson's parameter of β = 1.0 × 1010 Vm5/C3, verified from commercial BaTiO3‐based multilayer ceramic capacitors (MLCC), we show how the microstructure and the difference in core and shell conductivities alter the local fields generated and how this influences the voltage dependence of the effective permittivity. Systems that comprise a conductive core‐like material surrounded by a resistive shell experience little or modest voltage dependence due to the shell material providing shielding to large electric fields within the cores. Conversely, if the core material is more resistive than the shell material, substantial voltage dependence occurs with simulations showing over a 50% decrease in the effective permittivity. These simulations give improved understanding of voltage dependence and provide a method to help guide the design of future materials for MLCCs with improved performance.

The influence of sintering additives on densification and phase composition of ZrB2 – HfB2 composite

This work deals with the preparation of composites from the ZrB2-HfB2-MeX system (where: MeX = SiC, B4C, WC, MoSi2 and CrSi2). Three pressure-assisted sintering techniques were used to obtain the composites, i.e. hot-pressing (HP), spark-plasma sintering (SPS) and high pressure-high temperature (HPHT) sintering. Hot-pressing was selected as the most favourable sintering technique. The composites obtained via hot-pressing were characterized by high density and homogeneous microstructure. The work did not undermine or justify the need to reduce passivating oxide layers on boride grains. In the case of silicides, especially chromium silicide, there was a significant reduction in the sintering temperature of the ZrB2-HfB2 composites by about 500–600°C. In composites with the addition of silicides, there is a tendency to create complex solid solutions, which is visible as core-shell microstructures.

Real-Time Imaging of Interfacial Copper(II) Ion-Initiated Selective Etching in the Core Region of Single Cuprous Oxide-Bismoclite Core-Shell Microcrystals.

The core-shell microstructures are attracting much interest, most notably for their superior performance compared with their pure counterparts because of the interfacial effect. Comprehensively understanding the mechanism of the interfacial effect is critical but still elusive. Here, we report real-time dark-field optical microscopy (DFM) imaging of the selective etching in the core region of single cuprous oxide-bismoclite (Cu2O@BiOCl) core-shell microcrystals by I-. In situ DFM observations reveal that the reaction activity of Cu2O is significantly improved after coating the BiOCl shell layer, and the I- diffuses through the BiOCl shell and approaches the interface region, followed by etching the Cu2O core. During the etching process, two distinct reaction pathways, such as interfacial Cu2+-driven redox etching and confinement-governed dissolution, are identified. The interfacial Cu2+ is generated due to the coordination number difference at the core-shell interface. Moreover, according to the in situ DFM single-crystal imaging results, the ensemble adsorption capacity improvement for I- is also demonstrated in Cu2O@BiOCl core-shell microcrystals. These findings provide deep insights into the interfacial effect of core-shell microcrystals and establish a bridge between microscopic imaging and macroscopic practical application.

Evolution mechanism of the core-shell to homogeneous microstructure in immiscible alloy by semi-solid treatment under a high magnetic field

Immiscible alloys possess broad industrial applications, but the presence of immiscible gaps makes them highly susceptible to the formation of segregated microstructures, thus, a new method for obtaining a uniform distribution of fine minor separated phases needs to be explored. The present work focuses on the evolution mechanism of a CuCo immiscible alloy with a core-shell microstructure during semi-solid isothermal processing under a high magnetic field. The results showed that the microstructure changes from the core-shell structure of the initial sample to homogeneous microstructure after semi-solid treatment, regardless of whether a magnetic field is applied. The mechanism of microstructure evolution of the alloy during semi-solid treatment was revealed through in-situ experiment, in which Ostwald ripening and coalescence mechanisms led to grain coarsening, grain boundary remelting caused grain dissociation, and ultimately the grains underwent spheroidization. However, as a high magnetic field was applied, the average radius of the Co-rich particles decreased, and the particles were aligned in the direction of the magnetic field, forming a chain-like microstructure due to dipole-dipole interactions between the grains. The CuCo immiscible alloy with a uniform microstructure after semi-solid treatment exhibited a higher microhardness and saturation magnetization. This study offers a novel perspective for designing immiscible alloys with homogeneous microstructures as well as chain-like microstructures by utilizing semi-solid treatment combined with a magnetic field.

Rational design of agarose/dextran composite microspheres with tunable core–shell microstructures for chromatographic application

A new type of core-shell microsphere was prepared by a pre-crosslinking method, consisting of cross-linked agarose microspheres as the core and agarose-dextran as the shell. After optimizing the preparation process, the microspheres with a uniform particle size were obtained and characterized using cryo-scanning electron microscopy to determine their surface and cross-sectional morphology. Results from flow rate-pressure and chromatographic performance tests showed that the core-shell agarose microspheres were supported by the core microspheres and composed of composite polysaccharides, forming an interpenetrating polymer network structure as a hard shell. The core-shell agarose microspheres showed a 300.5 % increase in linear flow rate compared to composite polysaccharide microspheres prepared from shell materials and a 141.5 % increase compared to 6 % agarose microspheres. Additionally, the large pore structure of the shell combined with the fine pore structure of the core improved the material separation efficiency in the range of 0.1–2000 kDa. These findings suggest that core-shell natural polysaccharide microspheres have great potential as a separation chromatographic medium.

Construction of hierarchical ZnO-NiCo2O4-NiCo2O4 core-shell microstructure with efficient microwave absorption

Core-shell structural design is an attractive strategy to achieve high-performance microwave absorbers. Nevertheless, it still remains a problem to simultaneously obtain superior microwave dissipation and impedance matching for microwave absorption (MA) materials. In this work, ZnO-NiCo2O4-NiCo2O4 (ZNN) core–shell microstructure is designed and fabricated by covering NiCo2O4 nanosheets on the surface of ZnO nanorod and next growth of NiCo2O4 nanoparticles. With the synergies from the NiCo2O4 nanosheets improving the microwave attenuation capability and the NiCo2O4 nanoparticles increasing the impedance matching, ZNN possesses efficient MA performance: the strongest reflection loss is −59.93 dB at the corresponding thickness of 2.6 mm, and the maximum absorption bandwidth is 7.04 GHz at 2.4 mm, which covers the entire Ku-band. RCS simulation also indicates that ZNN has outstanding MA performance. Moreover, this study proposes a point for the utilization of nickel–cobalt oxides in MA materials, and offers a reference for the design of core–shell structural absorbers.

Temperature dependence of dielectric nonlinearity of BaTiO3 ceramics

In many commercially utilized ferroelectric materials, the motion of domain walls is an important contributor to the functional dielectric and piezoelectric responses. This paper compares the temperature dependence of domain wall motion for BaTiO3 ceramics with different grain sizes, point defect concentrations, and formulations. The grain boundaries act as significant pinning points for domain wall motion such that fine-grained materials show smaller extrinsic contributions to the properties below the Curie temperature and lower residual ferroelectric contributions immediately above the Curie temperature. Oxygen vacancy point defects make a modest change in the extrinsic contributions of undoped BaTiO3 ceramics. In formulated BaTiO3, extrinsic contributions to the dielectric response were suppressed over a wide temperature range. It is believed this is due to a combination of reduced grain size, the existence of a core-shell microstructure, and a reduction in domain wall continuity over the grain boundaries.

Superior high-temperature strength-ductility of TiB2–Ti2AlN/TiAl composite with core-shell microstructure

Herein, a novel core-shell structured TiAl composite consisting of nanoparticles “shell” and a near fully lamellar “core” was designed using a Ti–48Al–2Nb–2Cr alloy and Boron nitride nanoplates. By tailoring microstructure and nanoparticles strengthening, the TiAl composite exhibited a superior combination of strength and ductility at high temperature, which achieved an ultimate tensile strength of 514.2 MPa and an outstanding fracture strain of 18.8 % at 850 °C.

On dysprosium utilisation in multi-main-phase Nd–Dy–Fe–B magnets with core–shell microstructures

The development of high-performance Nd–Dy–Fe–B magnets that minimise the consumption of the scarce rare earth (RE) element Dy remains a major global scientific and technological quest. Here, we designed an alloy microstructure comprising of a uniform Dy-lean core–Dy-rich shell in a series of multi-main-phase (MMP) Nd–Dy–Fe–B magnets. The resulting MMP Dy1 and Dy3 magnets with an overall Dy level of 1 and 3 wt.% possessed values of 0.48 and 0.29 T/wt.% of coercivity increment per unit weight percentage of the Dy addition, respectively. Most importantly, the resulting MMP Dy3 magnet exhibited a high coercivity (2.38 T), an excellent thermal stability of the coercivity (|β| = 0.531%/°C), a high squareness factor (> 95%), all with little diminishment in the remanent magnetisation (1.35 T) and maximum energy product (43.6 MGOe). These properties are superior to the currently available sintered Nd–Dy–Fe–B magnets which utilise higher levels of Dy of 5 wt.%. Via magnetic and multi-scale microstructural characterisation experiments and micromagnetic simulations, the formation of the Dy-lean core–Dy-rich shell microstructure is rationalised via solid-state-diffusion and solution reprecipitation during liquid-phase sintering. The Dy-lean core–Dy-rich shell microstructure and the non-ferromagnetic low-Fe RE-rich grain boundary phase led to the synergistic magnetic performance. This is significant in the context of the MMP Nd–Dy–Fe–B magnets being applied to large-scale production. The present work establishes a pathway for the more sustainable utilisation of Dy in permanent magnets via formation of a uniform core–shell microstructure.

Chemical core-shell metastability-induced large ductility in medium-entropy maraging and reversion alloys

Maraging structural materials have been traditionally indicated as essential metallic alloys for hundreds of years. The highest strength of the aged martensite alloys requires the formation of high nanoprecipitate density; however, it often results in insufficient ductility (< ∼12%) which limits their application. Here, we describe how these alloys obtain enhanced ductility at high strength by injecting reversion-induced metastable austenite into the brittle microstructure, in which we develop a novel dual-phase medium-entropy Fe68Ni10Mn10Co10Ti1.5Si0.5 (at%) maraging alloys with a strength of 1.6 GPa and ductility of ∼25%. Generating the large fraction of austenite metastability with a chemical core-shell microstructure during a simple process of reversion drives profuse heterogeneities at chemical and structural states, including additional precipitation strengthening and transformation-induced plasticity effect. The combined metastability and heterogeneity, realized with heat-treatment techniques that are accessible processing routes in a wide range of academic and industrial applications, can provide a breakthrough to develop sustainable maraging materials with large ductility.

Facile synthesis of porous cellulose aerogel beads with tunable core–shell microstructures and physical properties

Cellulose aerogel beads (CABs) have emerged as advanced biomaterials with numerous engineering applications, including chromatography and drug release. In this study, porous core–shell CABs were synthesized using a dilute ethanol solution-substitution-assisted freeze-drying. The formation mechanism of the CABs and the effect of ethanol concentration on the core–shell microstructures and physical properties were investigated. Cellulose hydrogel beads (CHBs) were formed through the exchange/neutralization of acetic acid with tetraethylammonium hydroxide (TEAOH)/urea. The cellulose chains dissolved in the cellulose–TEAOH/urea droplets regenerated from the edge to the inside of the droplet in an acetic acid bath. Notably, adding ethanol at a concentration of 10% before freeze-drying can result in core–shell CABs with non-obvious structural shrinkage, large particle size, uniform pores, and high porosity. Ethanol molecules induce ice crystal growth to form more uniform ice crystals during the freezing process. Additionally, by altering the TEAOH/urea molar ratios and cellulose concentrations of cellulose solutions, well-shaped and porous CABs were prepared, demonstrating the feasibility and availability of dilute ethanol solution-assisted freeze-drying. Consequently, the as-fabricated CABs had a dense micro-shell (1–9 μm) and loose millimetric-core with anisotropic pores (2–6 μm), exhibiting low density (0.06–0.09 g/cm3), high porosity (87.0–91.5%), and noteworthy thermal stability.

Optimizing electromagnetic parameters to enhance the microwave absorbing properties of core–shell FeCo2O4@flaky FeSiAl composites

The high complex permittivity of flaky FeSiAl in microwave-absorbing materials leads to poor electromagnetic impedance matching and a narrow effective absorption bandwidth. To overcome this issue, we developed a novel approach by wrapping magnetic FeCo2O4 on the surface of flaky FeSiAl using a hydrothermal method, followed by calcination. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) were used to confirm the formation of a FeCo2O4@flaky FeSiAl composite with a well-defined core–shell microstructure. The prepared FeCo2O4@flaky FeSiAl composite exhibited a significantly reduced complex permittivity, which improved its electromagnetic impedance matching performance. When filled in paraffin with a thickness of only 1.6 mm, the composite demonstrated excellent electromagnetic wave absorption performance, with an effective absorption bandwidth of 5.60 GHz (RL < − 10 dB), indicating its potential in the field of microwave-absorbing materials. These results were achieved owing to the unique properties of the FeCo2O4@flaky FeSiAl composite, demonstrating its potential as a high-performance microwave absorber. This study may be of significant interest to researchers and engineers in the fields of magnetism and magnetic materials, especially those in the microwave field.

Electrical microstructure evolution of CaCu3Ti4O12 (CCTO) ceramics: From resistive and core shell-like to semiconducting grains

We show that CaCu3Ti4O12 (CCTO) ceramics present either giant (>104) or moderate (∼102) dielectric permittivity ε’ at room temperature (RT), depending on the grains resistivity. By sintering at 980 °C, a highly resistive bulk is obtained (resistivity of 5.8 GΩ cm) and no giant ε’ is verified. A semiconducting phase develops into the grains by sintering at 1050 °C, with a remaining thin resistive phase, hence forming a core-shell bulk microstructure. By increasing the sintering temperature to 1100 °C, the semiconducting phase of the bulk grows at the expenditure of the insulating shell, forming the well-known Internal Barrier Layer Capacitance (IBLC) structure. It is therefore proved that the giant ε’ in CCTO ceramics is linked to the grain boundaries dielectric response whose manifestation becomes resolved at RT when the bulk phase is semiconducting in nature. Such an effect is thermally originated during processing and related to Cu migration towards grain boundaries.