Search Results (26)

In this paper, the ceramic coating of thermal barrier coatings (TBCs) was prepared on the surface of the tube specimens by Electron Beam Physical Vapor Deposition (EB-PVD) process. Subsequently, a service simulation was conducted using a simulation device to analyze the failure behavior of the TBCs. The effects of high-temperature sintering and CaO-MgO-Al₂O₃-SiO₂ (CMAS) corrosion on the microstructural evolution, phase structural changes, and insulation performance of the thermal barrier coatings were investigated. The results indicated that with increasing high-temperature sintering time, the “feather” structures at the boundaries of the columnar grains evolve into the “tentacle” structure that facilitates the fusion of adjacent columnar grains, resulting in increased grain diameter and wider gaps. No transformation from t’-ZrO₂ to the monoclinic phase m-ZrO₂ occurred during the high-temperature sintering process. Over time, CMAS wets the coating surface and infiltrates the interior of the coating, causing corrosion to the Yttria-stabilised zirconia (YSZ) and accelerating sintering. A new phase, ZrSiO₄, was formed after corrosion without inducing the transition. Full article

Flexible perovskite solar cells (F-PSCs) have the advantages of high power-per-weight, solution processability, and bending durability and have emerged as a competitive photovoltaic technology for various applications. As the core electron transport layer (ETL) in n-i-p-type device configurations, the solution-processed SnO₂ generally suffers from serious defect stacking on films, compromising the charge transport properties and the performance of resulting devices. Herein, we proposed a media-filling strategy to optimize the contact quality at the buried interface by introducing Al₂O₃ nanoparticles on the SnO₂ surface. Rather than forming a compact insulating layer, the Al₂O₃ can fill the grain boundaries of SnO₂ and smooth the substrate surface. Optimized interfacial contact under careful concentration control can rationally minimize the contact area of the perovskite with the surface imperfections of SnO₂ to mitigate trap-assisted charge recombination. Furthermore, the reduced surface roughness of SnO₂ facilitates the uniform deposition and oriented growth of upper perovskite film. As a result, the target F-PSCs achieved an impressive efficiency of 23.83% and retained 80% of the initial performance after 5000 bending cycles at a radius of four mm. Full article

Relaxor ferroelectric film capacitors exhibit high power density with ultra-fast charge and discharge rates, making them highly advantageous for consumer electronics and advanced pulse power supplies. The Aurivillius-phase bismuth layered ferroelectric films can effectively achieve a high breakdown electric field due to their unique insulating layer ((Bi₂O₂)²⁺ layer)). However, designing and fabricating Aurivillius-phase bismuth layer relaxor ferroelectric films with optimal energy storage characteristics is challenging due to their inherently stable ferroelectric properties. In this work, lead-free CaBi_4-xLa_xTi₄O₁₅ films were synthesized using the sol–gel technique and a weakly coupled relaxor design. On one hand, the introduction of La³⁺ ions weaken the dipole–dipole interactions, thereby enhancing the relaxor behavior. Alternatively, the expansion of grain size is restricted to enhance the number of grain boundaries, which possess improved insulating properties. This leads to a higher breakdown electric field. The results indicate that CaBi_4-xLa_xTi₄O₁₅ (x = 1.0) films exhibit excellent recoverable energy storage density (70 J/cm³) and high energy efficiency (73%). Moreover, the film exhibited good temperature stability and frequency stability. This study not only identifies a promising material for dielectric film capacitors but also demonstrates that the energy storage capabilities of Aurivillius-phase bismuth layer ferroelectric films can be effectively modulated through a design incorporating weakly coupled relaxor characteristics. Full article

The effect of sintering temperature on the structural, magnetic, and dielectric properties of NiCr₂O₄ ceramics was investigated. A powder X-ray analysis indicates that the prepared nanocrystallites effectively inhibit the cooperative Jahn–Teller distortion, thereby stabilizing the high-temperature cubic phase structure with space group Fd-3m. Multiple transitions are confirmed by temperature-dependent magnetization M(T) data. Moreover, the magnetization value decreases and the Curie temperature increases with a decrease in the crystallite size. The low-temperature-dependent real permittivity (ε′-T) for a NiCr₂O₄ crystallite size of 78 nm exhibits a broad maximum at 40 K that is independent of frequency. This establishes a correlation between electric ordering and the underlying magnetic structure. The temperature dependency of the dielectric constant at fixed frequencies for both NiCr₂O₄ crystallite sizes rises with temperature for a certain range of frequencies. A significant improvement is evident: the dielectric constant (ε’) at room temperature reaches approximately 5738 for the sample with 28 nm crystallites, while the 78 nm crystallite sample shows a noticeable drop to ε’~174. The frequency-dependent conductivity curves for both types of NiCr₂O₄ nanocrystallites have different conductivity values. The lower-crystallite-size sample demonstrates higher conductivity values than the 78 nm crystallite size one. This observation is attributed to the decrease in crystallite size, which increases the number of grain boundaries and, consequently, scatters a higher number of charge carriers. Full article

Modern integrated circuits (ICs) take advantage of three-dimensional (3D) nanostructures in devices and interconnects to achieve high-speed and ultra-low-power performance. The choice of electrical insulation materials with excellent dielectric strength, electrical resistivity, strong mechanical strength, and high thermal conductivity becomes critical. Diamond possesses these properties and is recently recognized as a promising dielectric material for the fabrication of advanced ICs, which are sensitive to detrimental high-temperature processes. Therefore, a high-rate low-temperature deposition technique for large-grain, high-quality diamond films of the thickness of a few tens to a few hundred nanometers is desirable. The diamond growth rate by microwave plasma chemical vapor deposition (MPCVD) decreases rapidly with lowering substrate temperature. In addition, the thermal conductivity of non-diamond carbon is much lower than that of diamond. Furthermore, a small-grain diamond film suffers from poor thermal conductivity due to frequent phonon scattering at grain boundaries. This paper reports a novel MPCVD process aiming at high growth rate, large grain size, and high sp³/sp² ratio for diamond films deposited on silicon. Graphite paste containing nanoscale graphite and oxy-hydrocarbon binder and solvent vaporizes and mixes with gas feeds of hydrogen, methane, and carbon dioxide to form plasma. Rapid diamond growth of diamond seeds at 450 °C by the plasma results in large-grained diamond films on silicon at a high deposition rate of 200 nm/h. Full article

Si₃N₄ ceramic materials have great potential in the field of insulation in SF6 gas ultra-high-voltage transmission and transformation equipment due to their excellent insulation performance and thermal stability. In this paper, Y₂O₃-Al₂O₃ was used as a sintering aid to prepare high-density (>99%) Si₃N₄ ceramics through two-step pressureless liquid-phase sintering, and the mechanism of the influence of Y₂O₃-Al₂O₃ addition on the microstructure and electrical properties of Si₃N₄ ceramics was studied. The results showed that increasing the sintering aid content could increase the grain size of Si₃N₄ ceramics, while increasing the Y₂O₃ ratio could refine the grain size. When Y₂O₃-Al₂O₃ addition was 8% and the ratio was 5:3, the room temperature volume resistivity of Si₃N₄ ceramics was the highest, 7.33 × 10¹⁴ Ω·m, and the volume resistivity was the most stable when the sintering aid content was 12%. The internal carrier migration type of Si₃N₄ ceramics was mainly ion conduction, mainly along the grain boundaries. The temperature stability of the resistivity of Si₃N₄ ceramics could be improved by doping with Y³⁺ functional ions to reduce the potential barrier conductivity level and refine the grain size to improve the conduction path. The dielectric constant and dielectric loss of Si₃N₄ ceramics were mainly affected by interface polarization. They gradually increased with the increase in sintering aid addition. Temperature had little effect on dielectric constant and dielectric loss in the range of 20–80 °C. Full article

In this study, a capacitorless one-transistor dynamic random-access memory (1T-DRAM) based on a polycrystalline silicon (Poly-Si) metal-oxide-semiconductor field-effect transistor (MOSFET) with a storage layer separated using a separation oxide was designed and analyzed using technology computer-aided design (TCAD). The channel and storage layers were separated using a separation oxide to improve the inferior retention time of the conventional 1T-DRAM, and we adopted the underlap structure to reduce Shockley-Read-Hall recombination. In addition, poly-Si, which has several advantages, including low manufacturing cost and availability of high-density three-dimensional (3D) memory arrays, is used to easily fabricate silicon-on-insulator (SOI)-like structures. Accordingly, we extracted memory performance by analyzing the effect of grain boundary (GB). The proposed 1T-DRAM achieved a sensing margin of 14.10 μA/μm and a retention time of 251 ms at T = 358 K, even in the existence of a GB. Full article

A reentrant temperature dependence of the thermoresistivity ${\rho }_{\mathrm{xx}}(T)$ between an onset local superconducting ordering temperature $T_{\mathrm{loc}}^{\mathrm{onset}}$ and a global superconducting transition at $T=T_{\mathrm{glo}}^{\mathrm{offset}}$ has been reported in disordered conventional 3-dimensional (3D) superconductors. The disorder of these superconductors is a result of either an extrinsic granularity due to grain boundaries, or of an intrinsic granularity ascribable to the electronic disorder originating from impurity dopants. Here, the effects of Fe doping on the electronic properties of sputtered NbN layers with a nominal thickness of 100 nm are studied by means of low-T/high-${\mu }_{0}H$ magnetotransport measurements. The doping of NbN is achieved via implantation of 35 keV Fe ions. In the as-grown NbN films, a local onset of superconductivity at $T_{\mathrm{loc}}^{\mathrm{onset}}=15.72\mathrm{K}$ is found, while the global superconducting ordering is achieved at $T_{\mathrm{glo}}^{\mathrm{offset}}=15.05\mathrm{K}$, with a normal state resistivity ${\rho }_{\mathrm{xx}}=22\mathsf{\mu }\mathsf{\Omega }·\mathrm{cm}$. Moreover, upon Fe doping of NbN, ${\rho }_{\mathrm{xx}}=40\mathsf{\mu }\mathsf{\Omega }·\mathrm{cm}$ is estimated, while $T_{\mathrm{loc}}^{\mathrm{onset}}$ and $T_{\mathrm{glo}}^{\mathrm{offset}}$ are measured to be 15.1 K and 13.5 K, respectively. In Fe:NbN, the intrinsic granularity leads to the emergence of a bosonic insulator state and the normal-metal-to-superconductor transition is accompanied by six different electronic phases characterized by a N-shaped T dependence of ${\rho }_{\mathrm{xx}}(T)$. The bosonic insulator state in a s-wave conventional superconductor doped with dilute magnetic impurities is predicted to represent a workbench for emergent phenomena, such as gapless superconductivity, triplet Cooper pairings and topological odd frequency superconductivity. Full article

The study demonstrates that the introduction of the electrochemically inactive dielectric additive Li₂TiO₃ to LTO results in a strong decrease in the grain boundary resistance of LTO-Li₂TiO₃ (LTC) composites at a low concentration of Li₂TiO₃. With the increase in the concentration of Li₂TiO₃ in LTC composites, the grain boundary resistance goes through a minimum and increases again due to the growth of the insulation layer of small Li₂TiO₃ particles around LTO grains. For LTO-TiO₂ (LTT) composites, a similar effect was observed, albeit not as strong. It was found that LTC composites at low concentration of Li₂TiO₃ have unusually high charge–discharge capacity exceeding the theoretical value for pure LTO. This effect is likely to be caused by the occurrence of the electrochemical activity of Li₂TiO₃ in the vicinity of the interfaces between LTO and Li₂TiO₃. The increase in the capacity may be qualitatively described in terms of the model of two-phase composite in which there is the interface layer with a high capacity. Contrasting with LTC composites, in LTT composites, no capacity enhancement was observed, which was likely due to a noticeable difference in crystal structures of LTO and TiO₂ preventing the formation of coherent interfaces. Full article

The effects of the sintering conditions on the phase compositions, microstructure, electrical properties, and dielectric responses of TiO₂-excessive Na_1/2Y_1/2Cu₃Ti_4.1O₁₂ ceramics prepared by a solid-state reaction method were investigated. A pure phase of the Na_1/2Y_1/2Cu₃Ti_4.1O₁₂ ceramic was achieved in all sintered ceramics. The mean grain size slightly increased with increasing sintering time (from 1 to 15 h after sintering at 1070 °C) and sintering temperature from 1070 to 1090 °C for 5 h. The primary elements were dispersed in the microstructure. Low dielectric loss tangents (tan δ~0.018–0.022) were obtained. Moreover, the dielectric constant increased from ε′~5396 to 25,565 upon changing the sintering conditions. The lowest tan δ of 0.009 at 1 kHz was obtained. The electrical responses of the semiconducting grain and insulating grain boundary were studied using impedance and admittance spectroscopies. The breakdown voltage and nonlinear coefficient decreased significantly as the sintering temperature and time increased. The presence of Cu⁺, Cu³⁺, and Ti³⁺ was examined using X-ray photoelectron spectroscopy, confirming the formation of semiconducting grains. The dielectric and electrical properties were described using Maxwell–Wagner relaxation, based on the internal barrier layer capacitor model. Full article

Unconventional superconductivity in heavily boron-doped nanocrystalline diamond films (HBDDF) produced a significant amount of interest. However, the exact pairing mechanism has not been understood due to a lack of understanding of crystal symmetry, which is broken at the grain boundaries. The superconducting order parameter (Δ) of HBDDF is believed to be anisotropic since boron atoms form a complex structure with carbon and introduce spin-orbit coupling to the diamond system. From ultra-high resolution transmission electron microscopy, the internal symmetry of the grain boundary structure of HBDDF is revealed, which can explain these films’ unconventional superconducting transport features. Here, we show the signature of the anisotropic Δ in HBDDF by breaking the structural symmetry in a layered microstructure, enabling a Rashba-type spin-orbit coupling. The superlattice-like structure in diamond describes a modulation that explains strong insulator peak features observed in temperature-dependent resistance, a transition of the magnetic field-dependent resistance, and their oscillatory, as well as angle-dependent, features. Overall, the interface states of the diamond films can be explained by the well-known Shockley model describing the layers connected by vortex-like structures, hence forming a topologically protected system. Full article

(Nb⁵⁺, Si⁴⁺) co-doped TiO₂ (NSTO) ceramics with the compositions (Nb_0.5Si_0.5)_xTi_1−xO₂, x = 0, 0.025, 0.050 and 0.1 were prepared with a solid-state reaction technique. X-ray diffraction (XRD) patterns and Raman spectra confirmed that the tetragonal rutile is the main phase in all the ceramics. Additionally, XRD revealed the presence of a secondary phase of SiO₂ in the co-doped ceramics. Impedance spectroscopy analysis showed two contributions, which correspond to the responses of grain and grain-boundary. All the (Nb, Si) co-doped TiO₂ showed improved dielectric performance in the high frequency range (>10³ Hz). The sample (Nb_0.5Si_0.5)_0.025Ti_0.975O₂ showed the best dielectric performance in terms of higher relative permittivity (5.5 × 10⁴) and lower dielectric loss (0.18), at 10 kHz and 300 K, compared to pure TiO₂ (1.1 × 10³, 0.34). The colossal permittivity of NSTO ceramics is attributed to an internal barrier layer capacitance (IBLC) effect, formed by insulating grain-boundaries and semiconductor grains in the ceramics. Full article

The results of colossal magnetoresistance (CMR) properties of La_1-xSr_xMn_yO₃ (LSMO) films grown by the pulsed injection MOCVD technique onto an Al₂O₃ substrate are presented. The grown films with different Sr (0.05 ≤ x ≤ 0.3) and Mn excess (y > 1) concentrations were nanostructured with vertically aligned column-shaped crystallites spread perpendicular to the film plane. It was found that microstructure, resistivity, and magnetoresistive properties of the films strongly depend on the strontium and manganese concentration. All films (including low Sr content) exhibit a metal–insulator transition typical for manganites at a certain temperature, T_m. The T_m vs. Sr content dependence for films with a constant Mn amount has maxima that shift to lower Sr values with the increase in Mn excess in the films. Moreover, the higher the Mn excess concentration in the films, the higher the T_m value obtained. The highest T_m values (270 K) were observed for nanostructured LSMO films with x = 0.17–0.18 and y = 1.15, while the highest low-field magnetoresistance (0.8% at 50 mT) at room temperature (290 K) was achieved for x = 0.3 and y = 1.15. The obtained low-field MR values were relatively high in comparison to those published in the literature results for lanthanum manganite films prepared without additional insulating oxide phases. It can be caused by high Curie temperature (383 K), high saturation magnetization at room temperature (870 emu/cm³), and relatively thin grain boundaries. The obtained results allow to fabricate CMR sensors for low magnetic field measurement at room temperature. Full article

Among transition metal oxides, manganites have attracted significant attention because of colossal magnetoresistance (CMR)—a magnetic field-induced metal–insulator transition close to the Curie temperature. CMR is closely related to the ferromagnetic (FM) metallic phase which strongly competes with the antiferromagnetic (AFM) charge ordered (CO) phase, where conducting electrons localize and create a long range order giving rise to insulator-like behavior. One of the major open questions in manganites is the exact origin of this insulating behavior. Here we report a dc resistivity and magnetization study on manganite La${}_{1-x}$Ca${}_x$MnO${}_3$ ceramic samples with different grain size, at the very boundary between CO/AFM insulating and FM metallic phases $x=0.5$. Clear signatures of variable range hopping (VRH) are discerned in resistivity, implying the disorder-induced (Anderson) localization of conducting electrons. A significant increase of disorder associated with the reduction in grain size, however, pushes the system in the opposite direction from the Anderson localization scenario, resulting in a drastic decrease of resistivity, collapse of the VRH, suppression of the CO/AFM phase and growth of an FM contribution. These contradictory results are interpreted within the standard core-shell model and recent theories of Anderson localization of interacting particles. Full article

Herein, we report high electrocatalytic activity of monoclinic VO₂ (M1 phase) for the oxygen evolution reaction (OER) for the first time. The single-phase VO₂ (M1) nanoparticles are prepared in the form of uniformly covering the surface of individual carbon fibers constituting a carbon fiber paper (CFP). The VO₂ nanoparticles reveal the metal-insulator phase transition at ca. 65 °C (heating) and 62 °C (cooling) with low thermal hysteresis, indicating a high concentration of structural defect which is considered a grain boundary among VO₂ nanoparticles with some particle coalescence. Consequently, the VO₂/CFP shows a high electrocatalytic OER activity with the lowest η₁₀ (350 mV) and Tafel slope (46 mV/dec) values in a 1 M aqueous solution of KOH as compared to those of the vacuum annealed V₂O₅ and the hydrothermally grown VO₂ (M1), α-V₂O₅, and γ′-V₂O₅. The catalytically active site is considered V⁴⁺ components and V^4+/5+ redox couples in VO₂. The oxidation state of V⁴⁺ is revealed to be more favorable to the OER catalysis compared to that of V⁵⁺ in vanadium oxide through comparative studies. Furthermore, the amount of V⁵⁺ component is found to be increased on the surface of VO₂ catalyst during the OER, giving rise to the performance degradation. This work suggests V⁴⁺ and its redox couple as a novel active component for the OER in metal-oxide electrocatalysts. Full article