AbstractTwo‐step reactive flash sintering (TSRFS) was employed to achieve fast densification of high entropy pyrochlore (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Zr2O7 with suppressed grain growth and improved microstructural homogeneity. Theoretical density of ∼98.15% with a grain size of ∼684 nm was achieved by TSRFS, representing only half the grain size compared with conventional one‐step reactive flash sintering (RFS), while the total holding time of TSRFS was only 1.5 times that of RFS. Although longer duration in step 1 benefited faster densification, it was demonstrated that the shorter time in step 1 not only resulted in smaller grain size in TSRFS samples with identical densities but also helps mitigate the grain size heterogeneity between sample cores and surfaces. Therefore, the art of efficiently using TSRFS lies in the reasonable manipulation of the time and power in step 1 and 2, achieving a balance between densification, grain growth, and microstructural homogeneity.

AbstractThe viscosity data measured by penetration and parallel‐plate methods for As2Se3 glass and undercooled melt were compared with literature data. The MYEGA equation (log η0 = −4.67 ± 0.12, m = 43.2 ± 0.4, and T12 = 441.7 ± 0.3 K) was used for the description of the selected viscosity data, including melt region (15 orders of magnitude). The heat capacity data for As2Se3 glass, undercooled melt, and melt, as well as for crystalline As2Se3 were determined for low and medium‐range temperature intervals. These data were compared with previously reported data. Equations that describe the heat capacity of As2Se3 in a broad temperature interval were formulated. The values of the standard molar enthalpy, Δ0THm0, and entropy, Δ0TSm0, at T = 298.15 K are 26.202 kJ·mol−1 and 193.8 J·mol−1·K−1, respectively. The heat capacity data determined from very low temperatures were used for the calculation of crystal, glass, and melt entropies. These heat capacity temperature dependencies were used both for the estimation of the Kauzmann temperature (TK = 292.5 K) and the glass entropy at 0 K (S0 = 25.96 J·mol−1·K−1), and for the determination of the excess entropy. The proportionality between the viscosity of the As2Se3 melt and the excess entropy clearly indicates the applicability of the Adam–Gibbs (AG) model.

AbstractCeramic materials are widely used in engineering field because of their good physical and chemical properties. The poor mechanical properties of traditional ceramics seriously limit the development of ceramic materials and have attracted extensive attention since its birth. The development of high toughness, light weight, and functional ceramic materials has long been the pursuit of materials scientists. Since ancient times, nature has been the source of all kinds of human technological ideas, engineering principles, and major inventions. The functional structure of biology provides a good research object for the bionic design and preparation of ceramic materials. Therefore, it is necessary to summarize the functional structures and mechanisms in nature and biomimetic preparation technology. The purpose of this review is to provide guidance for the functionalized biomimetic design and efficient preparation of ceramic materials. Some typical functional examples in nature are introduced in detail, and several representative biomimetic preparation methods are listed. Finally, the performance and application status of biomimetic ceramics are summarized, and the future development direction of biomimetic ceramic materials is prospected.

AbstractMetakaolin geopolymers have gained much interest as a large‐scale, 3D printable material. It is well known that increasing temperature can expedite the geopolymerization reaction, but little is known about how the temperature variability of the printing environment can influence the rheology of fresh geopolymer pastes. In this study, the influence of temperature on the viscosity of potassium geopolymer pastes was investigated under constant shearing at rates of 25, 50, or 100 s−1, yield stress measurements, and oscillatory motion. The temperature range examined was 5°C–55°C, in systematic 5°C increments. It was found that temperatures above 30°C resulted in lower starting viscosities compared to colder temperatures, but eventually exhibited an exponential increase in viscosity as the geopolymerization chemical reaction became dominate. In addition, a higher shear rate delayed, but did not stop, the exponential increase in viscosity from occurring. Yield stress values also reflected an upward trend with increasing temperatures after a 30‐min temperature soak. Lastly, oscillatory measurements indicated that viable printing times for 50°C or above were as little as 50–60 min total and were compared to Vicat needle testing. Overall, the influence of temperature on rheological properties could be used to manipulate the geopolymer viscosity for optimum printing conditions.

AbstractAlthough many approaches have been implemented to tailor the strain in potassium sodium niobate (KNN)‐based ferroelectrics, they still suffer from poor strain compared to shape memory alloys and giant magnetostrictive materials. Herein, a strategy of periodic orthogonal poling is implemented in KNN‐based ceramics with multiphase boundaries, and the correlation between the amount of non‐180° domain and strain is established, revealing that the mechanisms of interfacial stresses facilitate reversible domain switching during the periodic orthogonal poling. Owing to the self‐generated interfacial stresses between the adjacent regions with different poling directions, an enhanced strain benefits from non‐180° domain switching, which is reversible during periodic orthogonal poling. The enhancement in strain decreases from O‐T to R‐O‐T to the R‐T phase boundary, which corresponds to the different quantity of the non‐180° domain, indicating that a large amount of non‐180° domains can further boost high strain under periodic orthogonal poling. Notably, a slight frequency‐dependent strain was observed across the frequency range of 1‒50 Hz. Therefore, an ideal strain can be further induced by enhancing the amount of reversible non‐180° domain switching in the multiphase boundary during periodic orthogonal poling, which can serve as a guide for the design of high‐performance KNN materials.

AbstractThe original model by Parthasarathy et al. for oxidation of MeB₂–SiC ultra‐high temperature ceramics (UHTCs) has been further expanded to include oxidation by water vapor and oxygen/water vapor mixtures. The revised model offers a more representative analysis of the composition of the glass phase and a thermodynamically consistent formulation for the processes governing the formation of the internal depletion zone. A key feature of the revised model is that it explicitly incorporates the out‐diffusion of CO(g) through the scale as a rate‐controlling parameter that defines the formation of internal depletion zone. In its present form, the expanded model explains some of the experimentally observed phenomena of oxidation of MeB₂–SiC UHTCs, such as the formation of MeO₂/B₂O₃ scale with embedded partially oxidized SiC at lower temperatures and limited growth of ZrO₂/borosilicate layer compared with the SiC‐depleted layer and the outer borosilicate layer in static oxidation at high temperatures. Application of the revised model to the experimental data from literature on oxidation of ZrB₂–SiC materials in air and water vapor is demonstrated and discussed.

AbstractAll‐solid‐state sodium‐ion batteries (NIBs) are emerging as a strong contender to the widely used lithium‐ion batteries due to their abundant resources and high safety performance. Solid‐state electrolytes, as the key component of SSBs, have gained widespread attention for their high safety and chemical stability. This study presented a novel solid glass‐ceramic electrolyte, Na3Sb0.75As0.25S4, which was synthesized by high ball milling and heat treatment. The findings demonstrate that elemental As can have a dual effect of improving ionic conductivity and successfully lowering H2S gas emission. Na3Sb0.75As0.25S4 exhibits superior performance in the cubic phase due to the partial replacement of Sb by As, with ionic conductivity up to 2.42 mS/cm and a low activation energy of 0.119 eV at room temperature. Furthermore, it releases only 0.017 cm3/g H2S in a conventional humidity environment for 30 min, much lower than the amount of 0.05 cm3/g H2S released by undoped Na3SbS4, making it an excellent candidate for all‐solid‐state NIB electrolyte.

AbstractThe field strength effect on fracture toughness was tested for three alkaline earth (AE) aluminoborosilicate (ABS) glasses. This work explores the impact of modifier field strength (FS) on macro‐mechanical properties in line with previous works which examined the FS effect on structure, hardness, crack resistance, and elastoplastic properties of alkali and AE‐ABS glasses. Fracture toughness (KIcVNB) was found to increase as modifier FS increased; and the elastoplastic ratio (HV/E) correlated well with plasticity, hardness, and fracture toughness. The purpose of this work is to examine the mechanical response of AE‐ABS glasses at a larger length scale in order to determine whether the field strength effect is active as was observed at lower length scales in previous works. The observed increase and decrease of the KIcVNB and HV/E, respectively, with increasing modifier FS, suggest a strong correlation between increasing fracture toughness and crack resistance with increasing plasticity for the AE‐ABS glasses studied.

AbstractThe hexaboride EuB6 has been proven to have qualities that theoretically travel from being electronic to being magneto‐caloric. Under GGA‐PBE and GGA + SOC + U schemes, first‐principles calculations have been used to examine the electronic band structure and density of states. The magnetic moment and the interaction constant have each been calculated using DFT. Additionally, the thermoelectric properties are considered within the particular transport restrictions in order to determine the dimensionless figure of merit (ZT). The extremum of the ZT for EuB6 is determined by using the Seebeck, electrical, thermal, and lattice conductivity coefficients, which are computed. At 1800 K, a maximum ZT of 0.22 is discovered. The computed values of optical conductivity, electron energy loss, absorption coefficient, dielectric tensor, refractive index, and extinction coefficient throughout the range of 0–13 eV anticipate the optical considerations of such an alloy. The infrared spectrum is that where this chemical is active. The critical temperature (Tc) has been determined using the Metropolis algorithm and the Monte Carlo simulation. The material exhibits a ferromagnetic to paramagnetic phase transition, as indicated by temperature‐dependent magnetization. The magnetocaloric efficiency of this material can be measured using the magnetic entropy change (−ΔSm) and the relative cooling power.