High‐Performance Flexible Sensors of Self‐Healing,Reversibly Adhesive,and Stretchable Hydrogels for Monitoring Large and Subtle Strains

Flexible sensors are becoming required in heath monitoring and human–machine interfaces, but it is still a challenge to develop flexible sensors with integrated high performances. Herein, high‐performance flexible sensors are fabricated that are self‐healing, reversibly adhesive, and utilizing stretchable hydrogels, which are composed of a pluronic F127 diacrylate (F127DA) cross‐linked poly(acrylic acid) (PAA) network and polydopamine (PDA), and further cross‐linked by Fe³⁺. The unique structure endows the resulting hydrogels (PAA‐PDA‐Fe³⁺ hydrogels) excellent self‐healing property, reversible adhesion property, mechanical stretchability, and electrical conductivity. On the basis of the excellent properties of PAA‐PDA‐Fe³⁺ hydrogels, flexible sensors with large sensing range (0–575%), high sensitivity (GF = 6.31), low response time (0.25 s), and excellent robustness (>500 cycles) are assembled and further applied in detecting both large and subtle strains induced by human motions and water ripple. Overall, this work not only provides an alternative clue to construct multi‐functional hydrogels, but also offers a new kind of high‐performance materials for flexible electronic devices, especially those for health monitoring and human–machine interface.     

Conductive double-network hydrogel for a highly conductive anti-fatigue flexible sensor

Improving the mechanical properties of hydrogels is a prime example of their large-scale, diverse applications. Herein, we report a one-pot method for preparing a double network system hydrogel where the polyvinyl alcohol served as the first polymer backbone, acrylamide as the second network, and N, N′-Methylenebisacrylamide as the cross-linker, and the prepared hydrogels presented excellent mechanical properties with 1168% tensile strain and 598 kPa compressive strength. Through the metal–ligand bonds, an electrolyte solution containing Cu²⁺ was introduced into the hydrogel, which exhibits higher water retention than other electrolyte-containing hydrogels. Specially, the hydrogel was able to retain water for 8 h under extreme dry conditions at 60°C. The GF value was calculated to be 0.124 when the strain was 0%–64.2%. Furthermore, the hydrogel flexible sensor can detect changes in ambient temperature. When the ambient temperature rises, its relative resistance also tends to rise. In conclusion, this hydrogel sensor offers great potential applications in flexible sensors.     

Novel superabsorbent materials from bacterial cellulose

A novel process for the production of superabsorbent materials (hydrogels) from bacterial cellulose (BC) was developed. Prior to crosslinking with a water‐soluble polyethylene glycol diacrylate (PEGDA), BC was first carboxymethylated and functionalized with glycidyl methacrylate. The degree of crosslinking influenced the swelling properties of the hydrogels. The use of greater amounts of PEGDA enhanced the formation of a thicker macromolecular network containing fewer capillary spaces in the crosslinked gel. The maximum water retention value of the hydrogels containing 2.5–3.5 mmol of carboxyl groups per gram of gel reached 125 g g^?1 in distilled water, and 29 g g^?1 in saline (0.9% NaCl solution). The highly porous hydrogel architecture with a pore size of 350–600 µm created a high specific surface area. This enables rapid mass penetration in superabsorbent applications. The superabsorbent hydrogels reached 80% of their maximum water absorption capacity in 30 min. © 2018 Society of Chemical Industry     

In situ polymerized Fe2O3@PPy/chitosan hydrogels as a hydratable skeleton for solar-driven evaporation

The world population is severely affected by water scarcity, and it is an alarming issue that needs to be addressed urgently. Seawater desalination by solar-driven evaporation is a promising technique to produce clean water. However, it is energy intensive and directs to a low water yield under natural sunlight. Therefore, the developments of new photothermal materials can reduce required energy for desired evaporation rates for efficient freshwater yield. Indeed, chitosan and polypyrrole-based polymers are natural cationic copolymers, and their nanocomposites present well deal of interest for hydrogel structures due to their hydratable skeletons, and solar-absorbing nature. Here, we report in situ polymerized Fe₂O₃@PPy/chitosan hydrogels as lightweight evaporation structures for solar-powered evaporation under brine solutions (3.5 wt%). The polymeric network of Fe₂O₃@PPy/chitosan hydrogels builds in cross-linked macroporous water channels, self-floating, and a wide range of omnidirectional solar absorption (96%). The state-of-the-art evaporation experiments demonstrate an efficient evaporation rate of water (1.80 kg m^–2 h^–1) and enhanced solar-to-vapor conversion efficiency (91%) as compared to other carbon-based evaporation structures, excluding heat losses under 1 kW m^–2 (one sun). Of note, the ultra-black hydrogel surface stored enough thermal energy (39.6°C) under one sun solar irradiance due to the cationic polymeric network of Fe₂O₃@PPy/chitosan. A single-step process for a freshwater supply that has been purified from various contaminants shows the potential of this device for real-world applications.     

Freezing as a path to build macroporous structures: Superfast responsive polyacrylamide hydrogels

Macroporous polyacrylamide (PAAm) hydrogels were prepared from acrylamide monomer and N,N′-methylene(bis)acrylamide (BAAm) crosslinker in frozen aqueous solutions. It was found that the swelling properties and the elastic behavior of the hydrogels drastically change at a gel preparation temperature of −6 °C. The hydrogels prepared below −6 °C exhibit a heterogeneous morphology consisting of pores of sizes 10–70 μm, while those formed at higher temperatures have a non-porous structure. PAAm networks with largest pores were obtained at −18 °C. The pore size of the networks increased while the thickness of the pore walls decreased by decreasing the monomer concentration. The hydrogels formed below −6 °C exhibit superfast swelling and deswelling properties as well as reversible swelling–deswelling cycles in water and in acetone, respectively.     

Semiconductor‐Insulator Transition in Undoped Rutile,TiO2, Ceramics

The electrical conductivity of undoped rutile ceramics is very dependent on sample processing conditions, especially the temperature and atmosphere during sintering and the subsequent cooling rate. Samples become increasingly semiconducting when quenched from temperatures above ~700°C without the need for a reducing atmosphere. Thus, samples quenched from 1400°C in air have conductivity ~1 × 10^?2 Scm^?1with activation energy ~0.01(1) eV over the temperature range 10–100 K, whereas similar samples that are slow cooled or annealed in air at 300°C–500°C are insulating with activation energy 1.67(2) eV and conductivity, e.g., 1 × 10^?7 Scm^?1 at 400°C. The very wide range of electrical properties is attributed to variations in oxygen content which are too small to be detected using thermogravimetry. Impedance analysis shows that, depending on cooling rate, partially oxidized samples may be prepared in which samples retain a semiconducting core, but have an oxidized outer layer.     

Microstructure,Ferroelectric, Piezoelectric,and Ferromagnetic Properties of Sc‐Modified BiFeO3–BaTiO3 Multiferroic Ceramics with MnO2 Addition

0.725BiFe_1?xSc_xO₃–0.275BaTiO₃ + y mol% MnO₂ multiferroic ceramics were fabricated by a conventional ceramic technique and the effects of Sc doping and sintering temperature on microstructure, multiferroic, and piezoelectric properties of the ceramics were studied. The ceramics can be well sintered at the wide low sintering temperature range 930°C–990°C and possess a pure perovskite structure. The ceramics with x/y = 0.01–0.02/1.0 sintered at 960°C possess high resistivity (~2 × 10⁹ Ω·cm), strong ferroelectricity (P_r = 19.1–20.4 μm/cm²), good piezoelectric properties (d₃₃ = 127–128 pC/N, k_p = 36.6%–36.9%), and very high Curie temperature (618°C–636°C). The increase in sintering temperature improves the densification, electric insulation, ferroelectric, and piezoelectric properties of the ceramics. A small amount of Sc doping (x ≤ 0.04) and the increase in the sintering temperature significantly enhance the ferromagnetic properties of the ceramics. Improved ferromagnetism with remnant magnetization M_r of 0.059 and 0.10 emu/g and coercive field H_c of 2.51 and 2.76 kOe are obtained in the ceramics with x/y = 0.04/1.0 (sintered at 960°C) and 0.02/1.0 (sintered at 1050°C), respectively. Because of the high T_C (636°C), the ceramic with x/y = 0.02/1.0 shows good temperature stability of piezoelectric properties. Our results also show that the addition of MnO₂ is essential to obtain the ceramics with good electrical properties and electric insulation.     

In vitro dynamic swelling behaviors of polyhydroxamic acid hydrogels in the simulated physiological body fluids

Summary Influence of some simulated physiological body fluids on the dynamic swelling behaviour of polyelectrolytic hydroxamic acid hydrogels (PHA) was investigated at 37 °C in vitro. The simulated physiological body fluids are distilled water, human sera, physiological saline (0.89 % NaCl), isoosmotic phosphate buffer at pH 7.4, gastric fluid at pH 1. 1, (gylicine-HCl buffer), urea (0.3 mol L⁻¹), and the aquatic solutions of K₂HPO₄ and KNO₃ (the sources of K+). The values of equilibrium swelling of PHA hydrogels varied in the range of 130–4625%, while the values of equilibrium fluid content of the hydrogels varied in the range of 57–97%. The initial rate of swelling, diffusional exponent, and, diffusion coefficient were calculated using swelling kinetics data. Diffusion of the fluids into the hydrogel was found to be non-Fickian character. The diffusion coefficients of the hydrogel varied between 0.6×10⁻⁶– 8.1×10⁻⁶ cm² s⁻¹. Received: 15 March 2000/Accepted: 18 December 2000     

Silicate and zirconium phosphate modified Nafion/PTFE composite membranes for high temperature PEMFC

The PEMFC performance of MEAs prepared from Nafion-212 (thickness 50 μm, Du Pont Co), porous poly(tetrafluoro ethylene) (PTFE, thickness 15 ~ 18 μm) film reinforced Nafion (NF, thickness 20 ± 2 μm), silicate hybridized NF (NF-Si, thickness 21 ± 2 μm), and zirconium phosphate hybridized NF (NF-Zr, thickness 21 ± 2 μm) membranes were investigated at 110 °C/ 51.7% RH, 120 °C/ 38.2% RH, and 130 °C/ 28.6% RH. We show PEMFC performances of these MEAs decrease in the sequence of: NF-Zr> NF-Si> NF> Nafion-212. The NF, NF-Si, and NF-Zr membranes have lower membrane thickness and lower Nafion content and require less water for proton transport than Nafion-212 at temperatures above 110 °C, and thus have higher conductivity and better PEMFC performance than Nafion-212. Incorporating silicate and zirconium phosphate into NF membranes enhances water retention of membranes at temperatures above 110 °C and improves PEMFC performances. Besides enhancing water retention, incorporating zirconium phosphate into membranes also provides more routes for proton transport via H⁺ exchange between H₃ ⁺O and HPO₄-Zr- and between H₂ ⁺PO₄-Zr- and HPO₄-Zr-. Thus NF-Zr has a higher conductivity and better PEMFC performance than NF and NF-Si.     

Dielectric temperature stability and energy storage performance of NBT-based ceramics by introducing high-entropy oxide

In this study, a high-entropy perovskite oxide Sr(Zr_0.2Sn_0.2Hf_0.2Ti_0.2Nb_0.2)O₃ (SZSHTN) was first introduced to Na_0.5Bi_0.5TiO₃ (NBT) lead-free ferroelectric ceramics to boost both the high-temperature dielectric stability and energy storage performance. Excellent comprehensive performance was simultaneously obtained in the 0.8NBT–0.2SZSHTN ceramic with high ε′ value (> 2000), wide ε′-temperature stable range (TCC < 5%, 52.4–362°C), low tanδ value in a wide range (<0.01, 90–341°C) and high energy storage performance (W_rec = 3.52 J/cm³, W_rec and η varies ±6.08% and ±7.4% from 20 to 150°C), which endows it the promising potential to be used in high-temperature environments.     

Hemocompatibility, swelling and thermal properties of hydrogels based on 2-hydroxyethyl acrylate, itaconic acid and poly(ethylene glycol) dimethacrylate

Two series of novel hydrogels, based on 2-hydroxyethyl acrylate (HEA), itaconic acid (IA), and two poly(ethylene glycol) dimethacrylates (PEGDMA), of different ethylene glycol chain lengths, were prepared by free radical crosslinking copolymerization. The influence of different ethylene glycol chain lengths and concentration in P(HEA/IA/PEGDMA) hydrogels on biocompatibility, swelling and thermal properties was investigated. All samples in contact with blood showed a mean hemolysis value <1.0 % in the direct contact assay, and even <0.5 % in the indirect contact assay, for in vitro testing conditions. Swelling studies, conducted in a physiological pH and temperature range, showed pH sensitivity and relatively small changes of equilibrium swelling with temperature, which varied with PEGDMA molecular weight. The glass transition temperatures (T _g) of P(HEA/IA/PEGDMA) networks were in the range 28.1–36.9 °C, respectively, and also dependent on copolymer composition. Due to good biocompatibility, favorable swelling, and thermal properties these hydrogels show good potential for biomedical uses.     

The structural,dielectric, electrocaloric,and energy storage properties of lead-free Ba0·90Ca0·10Zr0·15Ti0·85O3

Lead-free ferroelectric materials with Electrocaloric Effect (ECE) and recoverable energy (W_rec) represent a major breakthrough in the technological race for manufacturing low-cost and eco-friendly smart multifunctional devices. Here, guided by the benefits resulting from successive ferroelectric-ferroelectric (F–F) and ferroelectric-pseudo cubic (F-PC) transitions including broad operational temperature span, lead-free Ba_0·90Ca_0·10Zr_0·15Ti_0·85O₃ (BCZT) ferroelectric ceramic located near the phase convergence region was prepared using the conventional solid-state solution. In this study, the systematic investigation of structural and microstructural properties via X-Ray Powder Diffraction (XRPD), scanning electron microscopy (SEM), temperature-dependence Raman spectroscopy and dielectric properties confirm the formation of a pure perovskite material which undergoes consecutive R3c-R3m, R3m-Amm2, Amm2-P4mm (F–F) phase transitions followed by (F-PC) transition in a wide temperature range centered around room temperature (RT). Polarization-Electric field (P-E) measurements, revealed the coexistence of Positive Electro-Caloric Effect (PECE) and Negative Electro-Caloric Effect (NECE) in a wide temperature span of [-40 °C, 95 °C]. More interestingly, we reached a large absolute temperature change (ΔT) and EC coefficient (ξ) values of (5.505 °C, 1.847 KmmkV^?1), (0.861 °C, 0.289 KmmkV^?1) and (1.897 °C, 0.637 Kmm kV^?1) registered respectively at about ?5, 42.5 and 74.5 °C under an electric field of 29.80 kVcm^?1. This work will promote further studies on lead-free BCZT ceramics towards multifunctional environmentally-friendly material promising for solid-state cooling technology.     

Highly stretchable,tough, and self‐recoverable and self‐healable dual physically crosslinked hydrogels with synergistic “soft and hard” networks

Strength, toughness and self‐recoverability are among the most important properties of hydrogels for tissue‐engineering applications. Yet, it remains a challenge to achieve these desired properties from the synthesis of a single‐polymer hydrogel. Here, we report our one‐pot, a monomer‐polymerization approach to addressing the challenge by creating dual physically crosslinked hybrid networks, in particular, synergistic “soft and hard” polyacrylic acid‐Fe³⁺ hydrogels (SHPAAc‐Fe³⁺). Favorable mechanical properties achieved from such SHPAAc‐Fe³⁺ hydrogels included high tensile strength (about 1.08 MPa), large elongation at break (about 38 times), excellent work of extension (about 19 MJ m^?3), and full self‐recoverability (100% recovery of initial properties within 15 min at 50°C and within 60 min in ambient conditions, respectively). In addition, the hydrogels exhibited good self‐healing capabilities at ambient conditions (about 40% tensile strength recovery without any external stimuli). This work demonstrates that dual physical crosslinking combining hydrophobic interaction and ionic association can be achieved in single‐polymer hydrogels with significantly improved mechanical performance but without sacrificing favorable properties. POLYM. ENG. SCI., 59:145–154, 2019. © 2018 Society of Plastics Engineers     

Highly sensitive flexible strain sensor based on carbon nanotube/styrene butadiene styrene@ thermoplastic polyurethane fiber with a double percolated structure

The combination of a high sensitivity and a wide strain detection range in conductive polymer composites-based flexible strain sensors is still challenging to achieve. Herein, a double-percolation structural fiber strain sensor based on carbon nanotubes (CNT)/styrene butadiene styrene (SBS)@thermoplastic polyurethane (TPU) composite was fabricated by a simple melt mixing and fused filament fabrication strategy, in which the CNT/SBS and TPU were the conductive and insulating phases, respectively. Compared with the sensor without the double percolated structure, the CNT/SBS@TPU sensor achieved a lower percolation threshold (from 2.0 to 0.5 wt%, a reduction of 75%), and better electrical and sensing performance. It is shown that the strain detection range of the CNT/SBS@TPU sensor increases with increasing CNT loading. An opposite trend was observed for the sensitivity. The 1%-CNT/SBS@TPU sensor exhibited a high conductivity (1.08 × 10⁻³ S/m), high sensitivity (gauge factor of 2.65 × 10⁶ at 92% strain), wide strain detection range (0.2%–92% strain), high degree of linearity (R² = 0.954 at 0–10% strain), broad monitoring frequencies (0.05–0.5 Hz), and excellent stability (2000 cycles). Moreover, the CNT/SBS@TPU sensor was shown to successfully monitor a range of human physiological activities and to be capable of tactile perception and weight distribution sensing.     

Solution processed,vertically aligned,AZO nanocolumn array for chemiresistive sensor application with UV-enhanced sensitivity

In this work, a wide and highly sensitive chemiresistive sensor has been developed based on the AZO nanocolumn array film. This is meant for the room detection of H₂O₂ under UV illumination. A cost-effective one step multi-layers growth process was adopted for the synthesis of the AZO nanocolumn array. The experimental studies were done by scanning electron microscopy (SEM), transmission and electron microscopy (TEM).Then X-ray diffraction confirmed that the AZO column array was closely packed, connected, vertically aligned, and polycrystalline, with a high surface area. This structure ensures better electrical conduction over random and separated nanostructures. The hall-effect measurement indicates that the AZO film was n-type, with high conductivity (3.60 × 10³ Ωcm), high carrier density (11.3 × 10²⁰cm⁻³) and with acceptable mobility (0.95 cm²/Vs). The x-ray photoemission spectroscopy suggests that the AZO film consists of a large amount of adsorbed oxygen-related species at the sheath layer of the thin-film, which is vital for sensors. By the UV light activation, sensors based on the AZO nanocolumn array exhibited enhanced H₂O₂ detection properties at room temperature. At a concentration from 15 μM to 30 mM, H₂O₂ sensitivity evaluated by relative response was remarkably increased from 15% to 36%. The operation under ambient conditions and wide range sensing shows that this chemiresistive AZO sensor is adequate for biomedical and environmental applications.     

Behaviors of Chemically Crosslinked CAAMPS Hydrogels in Uptake of Uranyl Ions from Aqueous Solutions

Uranyl ion adsorption from aqueous solutions has been investigated by chemically crosslinked (C) polyelectrolyte acrylamide/2-acrylamido-2-methyl-1-propanesulfonic acid (CAAMPS) hydrogels. CAAMPS hydrogels with various compositions were prepared from ternary mixtures of acrylamide (A), 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), and water by free radical polymerization in an aqueous solution using multifunctional crosslinkers such as ethylene glycol dimethacrylate (EGDMA) and 1,4 butanediol dimethacrylate (BDMA). The swelling equilibrium of polyelectrolyte copolymer gels containing of CAAMPS hydrogels has been studied as a function of copolymer composition. Swelling experiments were performed in water at 25°C, gravimetrically. The influence of AMPS content in hydrogels was examined. The weight-swelling ratio of CAAMPS hydrogels was increased up to 127.03 (for 300 mg AMPS and crosslinked by EGDMA) and 93.32 (for 300 mg AMPS and crosslinked by BDMA), while acrylamide hydrogels swelled up to 10.27 (crosslinked by EGDMA) and 10.06 (crosslinked by BDMA). Uranyl ion adsorption from aqueous solutions was studied by batch sorption technique at 25°C. The effect of uranyl ion concentration and mass of AMPS on the uranyl ion adsorption were examined. In the experiments of the sorption, L type sorption in the Giles classification system was found. Finally, the amount of sorbed uranyl ion per gram of dry hydrogel (q) was calculated to be 0.67 × 10^?3–2.11 × 10^?3 mol uranyl ion per gram for CAAMPS hydrogels. Removal effiency of uranyl ions (RE%) was changed range 9.05–29.92%. The values of partition ratio, (K _d ) of uranyl ions was calculated to be 0.10–0.43 for CAAMPS hydrogels.     

Temperature‐Stable Relative Permittivity from −70°C to 500°C in (Ba0.8Ca0.2)TiO3–Bi(Mg0.5Ti0.5)O3–NaNbO3 Ceramics

Temperature‐stable relaxor dielectrics have been developed in the solid solution system: 0.45Ba_0.8Ca_0.2TiO₃–(0.55 ? x)Bi(Mg_0.5Ti_0.5)O₃–xNaNbO₃. Ceramics of composition x = 0 have a relative permittivity ?_r = 950 ± 15% over a wide temperature range from +70°C to 600°C. Modification with NaNbO₃ at x = 0.2 decreases the lower limiting temperature to ?70°C, but also decreases relative permittivity such that ?_r ~ 600 ± 15% over the temperature range ?70°C to 500°C. For composition x = 0.3, the low‐temperature dispersion in loss tangent, tan δ, (at 1 kHz) shifts to lower temperature, giving tan δ values ≤0.02 across the temperature range ?60°C to 300°C in combination with ?_r ~ 550 ± 15%. Values of dc resistivity for all samples are of the order of 10¹⁰ Ω m at 250°C and 10⁷ Ω m at 400°C.     

Transport properties of sealants for high-temperature electrochemical applications: RO–BaO–SiO2 (R = Mg,Zn) glass–ceramics

The electrical properties and oxygen permeability of glass–ceramics 55SiO₂–27BaO–18MgO, 55SiO₂–27BaO–18ZnO and 50SiO₂–30BaO–20ZnO (%mol), which possess thermal expansion compatible with that of yttria-stabilized zirconia (YSZ) solid electrolytes, were studied between 600 and 950 °C in various atmospheres. The ion transference numbers, determined by the modified electromotive force (e.m.f.) technique under oxygen partial pressure gradients of 21 kPa/(1–8) × 10² Pa and 21 kPa/(1 × 10⁻¹⁸–2 × 10⁻¹²) Pa, are close to unity both under oxidizing and reducing conditions. The electronic contribution to the total conductivity increases slightly on increasing temperature, but is lower than 2% and 7% for the Zn- and Mg-containing compositions, respectively. The conductivity values measured by impedance spectroscopy vary in the range (1.4–7.8) × 10⁻⁶ S/cm at 950 °C under both oxidizing and reducing conditions, with activation energies of 122–154 kJ/mol and a minor increase in H₂-containing atmospheres, indicating possible proton intercalation. In agreement with the electrical measurements which indicate rather insulating properties of the glass–ceramics, the oxygen permeation fluxes through sintered sealants and through sealed YSZ/glass–ceramics/YSZ cells are very low, in spite of an increase of 15–40% during 200–230 h under a gradient of air/H₂–H₂O–N₂ due to slow microstructural changes.     

Poly(N,N-dimethylaminoethyl methacrylate)/graphene oxide hybrid hydrogels: pH and temperature sensitivities and Cr(VI) adsorption

Different amounts of graphene oxide (GO) were incorporated to N,N-dimethylaminoethyl methacrylate (DMAEMA), fabricating a series of pH and temperature dual sensitive PDMAEMA/GO hybrid hydrogels by in situ polymerization. Their microscopic network structures as well as swelling properties and Cr(VI) adsorption were characterized. The equilibrium swelling ratios (ESR) of hydrogels increased significantly with 0.5 wt% GO feeding of DMAEMA amount, and then decreased with further GO loading increasing. All hydrogels showed obvious deswelling when pH value of swelling mediums increased from 5 to 10 gradually. At pH 7, hydrogels revealed slight ESR increment with temperature up to 50 °C, above which obvious deswelling occurred. In pH 8 buffer, 0.5 wt% of GO loading triggered lower critical solution temperature (LCST) to decrease by 3 °C, and 2–7 °C increment was observed when 1–6 wt% of GO was loaded, as compared with that of GO-free PDMAEMA hydrogel. Cr(VI) adsorption of hydrogels was also improved by the introduction of GO to some extent, and the maximum Cr(VI) adsorption of 180 mg/g was realized, indicating that the obtained PDMAEMA/GO hybrid hydrogels possess excellent adsorption performance.     

Construction of multiple heterogeneous interface and its effect on microwave absorption of SiBCN ceramics

Iron-containing siliconboron carbonitride (SiBCN) ceramics with multiple heterogeneous interfaces were fabricated using the microstructural design and polymer-derived ceramics (PDC) approach. The characterization results revealed the in-situ generation of nanocrystals, including graphite, belt-like silicon nitride (Si₃N₄), and silicon carbide (SiC) whiskers, in amorphous SiBCN matrix after annealing. At the same time, these dielectric lossy phases successfully constructed multiple heterogeneous interfaces and three-dimensional network structures. Consequently, the conductivity of the ceramics increased from 4.49 × 10⁻⁹ (annealed at 800 °C) to 0.67 × 10⁻⁴ S cm⁻¹ (annealed at 1600 °C). The real part of permittivity improved from 4.57–3.36 (annealed at 800 °C) to 10.90–8.38 (annealed at 1600 °C) in the frequency range of 2–18 GHz. The formation of multiple heterogeneous interfaces caused interfacial polarization and increased the multiple relaxations, which ultimately led to a superior microwave absorption property with a minimum reflection loss (RL_min) of −34.28 dB and an effective absorption bandwidth (EAB) of 3.76 GHz (8.64–12.4 GHz).