Journal of the American Ceramic Society最新文献

A comprehensive investigation into the dynamic hysteresis behavior of the low temperature sintered 0.4PZN–0.6PZT ceramics across a wide range of electric field frequency, and temperature was carried out in the present study. Our findings from the electric field and frequency dependent scaling analysis at 303 K revealed distinct domain dynamics having three stages of polarization reversal mechanism with a breakdown frequency (f_b) of 5 Hz. Temperature dependent scaling analysis till 503 K showcased the influence of thermal energy especially in the stage-I and stage-II of the polarization reversal mechanism resulting in enhanced domain wall mobility with reduced switching time at a lower electric field. The power-law temperature scaling relations for hysteresis area 〈A〉, remanent polarization (P_r), and coercivity (E_C) took the form of A ∝ T ^0.1468, P_r ∝ T ^−0.5577, and E_C ∝ T ^−0.68272, respectively. The decay of the derived exponent values with temperature corresponding to 〈A〉, P_r, and E_C was minimal as compared to the other reported soft PZT and lead-free systems. This study provided information on the influence of temperature toward domain wall motion, domain nucleation, and domain switching, and it will be useful for designing devices that demand high reliability and thermal stability.

This work aims at understanding the oxidation mechanism of a TiC–SiC nanocomposite ceramic material. Samples were subjected to heat treatments up to 1400°C under air, varying the relative density of the composite, the heating rate, and the dwell time. The weight variations were followed by thermogravimetric analyses coupled with mass spectrometry. The oxidized samples were then characterized by scanning electron microscopy on cross-sections (SEM-EDX) and their microstructure and composition were studied by transmission electron microscopy (TEM-EDX). The oxidation process was also followed by in situ high-temperature X-ray diffraction and high-temperature environmental scanning electron microscopy. Until 1000°C, the formation of a multilayer alteration scale was observed, with a dense and protective SiO₂ layer. Above 1200°C, this layer showed cracks, and the oxidation was increased. Based on the results, a three-step mechanism was proposed for the temperature-dependent conversion of TiC and SiC to the subsequent oxides.

Grain boundaries in protonic ceramic cell (PCC) electrolytes hinder proton transport, reducing interfacial conductivity. In multicomponent PCC electrolytes, the inclusion of sintering aids further accentuates the complexity of grain boundaries. In this study, we synthesize nanocrystalline BaCe_0.4Zr_0.4Y_0.1Yb_0.1O_3−δ thin films via pulsed laser deposition and analyze their grain boundary character distributions using orientation data collected by precession electron diffraction technique. The results reveal an anisotropic distribution of grain boundary characters, with notably high populations of 180°-tilt and twist grain boundaries. These findings provide critical insights into identifying the predominant grain boundaries in this PCC electrolyte material, assessing the vast five-dimensional grain boundary space.

All-solid-state lithium-ion batteries, employing solid electrolytes, offer a promising solution to address safety concerns inherent in conventional lithium-ion batteries. Among the various types of Li-ion solid electrolytes, LiTi₂(PO₄)₃ (LTP) with the Na Super Ionic CONductor (NASICON) structure stands out as a particularly attractive material, despite its relatively low ionic conductivity at room temperature. One approach to enhance the performance of LTP solid electrolytes involves modifying the network size or redistributing Li cations and vacancies within the adjacent sites of the NASICON structure. Therefore, this study seeks to replace lithium ions with divalent cations, thereby increasing the concentration of vacancies, and facilitates the migration of Li⁺ ions between adjacent partially populated M1 sites. Introducing divalent elements not only augments vacancies in the lithium sites but also induces variations in local disorder within NASICON structures. Consequently, NASICON compounds, M^II_x/2Li_1−xTi₂(PO₄)₃ (M^II = Mg, Zn, and Cd), were synthesized via the sol–gel method, and their structural, microstructural, and electrical properties were thoroughly analyzed using a variety of techniques. The presence of divalent cations in the M1 site results in a reduction of symmetry and an enhancement of local disorder. A correlation between ionic conductivity and structure was established, which was linked to the disorder of lithium atoms within the structure. Electric modulus formalism was employed to explore electric relaxation, revealing that the diffusion and relaxation processes are thermally activated.

This study explores the effect of single doping with different rare earth elements (Y, La, and Yb) on the structural, morphological and electrical properties of CaMnO₃ bulk ceramics, aiming to improve their thermoelectric performance. Ca_(1-x)R_xMnO₃ (R = Y, La, Yb; x = 0, 0.05, 0.10) samples were synthesized via a solid-state reaction. XRD analysis confirmed the thermoelectric CaMnO₃ phase as the major one, with orthorhombic perovskite structure. Small amounts of secondary phases (CaMn₂O₄ and Mn₂O₃) were also detected in some doped samples. The addition of dopants influenced the unit cell parameters, producing a shift to lower 2θ angles, confirming their incorporation into the ceramic structure. SEM micrographs revealed a significant reduction in grain size upon doping. Electrical resistivity measurements showed a metallic behavior for all doped samples. The Y-doped samples exhibited the highest resistivity values while the Yb-doped samples showed the lowest values (6.8 mΩ cm for the 0.10 doped one), which are among the lowest found in literature for this compound. The Seebeck coefficient values show minor changes for 0.05 doped samples when they decreased with increasing concentration of dopant. Consequently, the highest values were observed for 0.05-doped sample (−215 µV/K), independently of the dopant. This value is much higher than the ones typically reported in the literature. The highest value of the power factor was calculated for the 0.05 Yb doped sample, reaching approximately 0.56 mW/K²·m at 800°C. This value is higher than the best presented in the literature for this compound, to the best of our knowledge, and suggests that Yb³⁺ doping greatly enhances the high-temperature thermoelectric performance of bulk CaMnO₃ ceramics, making it a promising dopant for high-efficiency thermoelectric materials.

The effects of atmosphere and cerium content on the densification and the final microstructure of homogeneous U_1-xCe_xO_2+δ solid solutions (x = 0.10; 0.25; 0.50) were investigated. Dilatometric studies first revealed that while the cerium content only slightly modifies sintering under an Ar/H₂ atmosphere, a change of the gas to argon dramatically modifies densification kinetics. As a result, samples prepared under Ar/H₂ exhibit a dense microstructure with micrometric grains. Conversely, samples sintered under argon appeared to be less densified but with larger grains. These changes were correlated with the variation of the final O/M stoichiometry (M = U+Ce) and illustrated by the construction of sintering maps. Finally, grain growth was found to be driven by grain boundary motion when the O/M ratio remained close to 2.00, while usual power laws did not apply for most hyper-stoichiometric samples. The first values of activation energy for the sintering of U_1-xCe_xO_2+δ solid solutions under an Ar/H₂ atmosphere were also determined.

Borosilicate glass has been employed for immobilization of high-level radioactive waste (HLW). During long-term geological disposal, the irradiation damage from radionuclides and the potential risk of groundwater corrosion may compromise the integrity of HLW containment. In this work, Na-borosilicate and Zr-Na borosilicate glasses were irradiated with 2 MeV He ions. The leaching behaviors of both glass types were investigated using the MCC-1 method at 90°C. Different techniques, including Raman spectroscopy, Fourier Transform Infrared Spectroscopy, Inductively Coupled Plasma Optical Emission Spectroscopy, and Time-of-Flight Secondary Ion Mass Spectrometry, were employed to analyze the leached samples and the leachate. The results indicated that He ion radiation could accelerate the leaching process of borosilicate glasses. The leaching rate of He irradiated borosilicate glass was between that of the pristine and Xe irradiated borosilicate glasses. This finding enhances our understanding of the discrepancies in leaching behavior associated with alpha particles and recoil nuclides during alpha decay.

BaTiO₃ (BTO) thin films were deposited on LaNiO₃ (LNO)/SiO₂/Si substrates by magnetron sputtering, and the LNO thin film was deposited as a bottom electrode and a buffer layer. The bipolar resistive switching (RS) behaviors have been observed in the Al/BTO/LNO devices, and the effect of illumination conditions on the RS behavior was investigated. The set voltage was effectively reduced by the photogenerated carrier, and a greatly improved OFF/ON resistance ratio of ∼120 was achieved under high light conditions. The Al/BTO/LNO devices showed good endurance and retention performance. The conduction mechanisms of the Al/BTO/LNO devices have been discussed based on the migration of defects and photogenerated carriers. These results facilitated a deeper study of BTO-based multifunctional storage devices and demonstrated the tunable photoresponse characteristic.

This study investigates the subcritical crack growth behavior of a 3D woven SiC-based composite under cyclic loading at 1100°C in air. The composite was subjected to monotonic tension and tension–tension fatigue tests using both unnotched dumbbell-shaped and edge-notched specimens. Detailed examinations of crack growth were conducted through optical microscopy and X-ray computed tomography (XCT). While the monotonic tensile strength was found to be insensitive to millimeter-sized notches, the fatigue strength was reduced by 20%–30% in the presence of such notches. Crack growth was found to be irregular and chaotic at the mesoscale, influenced by the complex interplay of chemical and mechanical processes and spatial variability in the composite microstructure. The study emphasizes the importance of XCT imaging for accurate internal crack tracking. It also proposes a phenomenological fracture mechanics model to describe crack growth and lifetime prediction, highlighting the nonmonotonic nature of crack growth rates.

We successfully produced a dopant-free oxygen-defective HfO_2−x film that exhibit room-temperature ferromagnetism via a heat treatment of metallic Hf foil at 1673 K for 10 h under an oxygen partial pressure of 1.0 × 10⁻⁴ atm. The sample, which exhibits ∼50% transmission of visible light, demonstrates room-temperature ferromagnetism, with saturation and residual magnetizations of ∼0.05 emu/g and ∼0.005 emu/g, respectively. The HfO_2−x film comprises columnar grains several hundred nanometers wide and several micrometers long. High-angle annular dark-field scanning electron microscopy observations indicated that the tetragonal HfO₂ structure was distributed in nanodomains within the monoclinic HfO₂ grains; that is, the films exhibited a hybridized microstructure. The tetragonal HfO₂ structure would be mainly due to the introduction of oxygen deficiencies, which led to the room-temperature ferromagnetism.