Developing high-efficiency sintering technologies with mild conditions is crucial for reducing the energy consumption and manipulating the performance of ceramics. However, sintering ceramics at low temperatures in short times without pressure is challenging because of their high melting points. Inspired by microwave resonance and dissolution‒precipitation phenomena, an energy efficient sintering, microwave cold sintering process (MW-CSP), is proposed here to densify high-performance ceramics with significantly reduced sintering times and temperatures under pressureless conditions during the sintering stage. A range of ceramics, including chlorides, oxides, phosphates, and molybdates, with various applications, have been shown to be well sintered by MW-CSP. The transmission electron microscopy (TEM) and phase-field simulation results demonstrate that the combination of the transient liquid phase and microwave resonance improves the driving force of sintering. Compared with those of other pressureless sintering technologies, the mechanical and dielectric properties of the selected materials are improved by 50%–95%, whereas the energy consumption of MW-CSP is dramatically reduced by more than 97%. These findings highlight the great potential of MW-CSP in efficiently densifying high-performance ceramics, opening up possibilities for energy-saving sintering.

As electronic devices become increasingly miniaturized and demand greater integration, traditional packaging technologies face substantial challenges in meeting the needs for high-frequency performance and system reliability. Ceramic materials, known for their excellent dielectric properties and thermal stability, are promising candidates for advanced packaging applications. However, conventional high-temperature densification processes, which often exceed 1000 ℃, restrict their compatibility with temperature-sensitive components in modern electronic systems. To overcome this limitation, we propose a novel approach to densify Al₂O₃−H₃BO₃ ceramic at room temperature under low uniaxial stress. It is found that a H₃BO₃ facilitates plastic deformation in the medium of deionized water, enhancing the densification of Al₂O₃−H₃BO₃ ceramics even at minimal uniaxial stress. The resulting material exhibits a high relative density of over 96% and possesses excellent microwave dielectric properties (relative permittivity ε_r: 2.84–5.37; Q × f values: 12,924–69,000 GHz; resonant frequency τ_f values: −156.94 10⁻⁶ ℃⁻¹ to −73.42 10⁻⁶ ℃⁻¹) and thermal conductivity (λ values: 1.96–5.96 W·m⁻¹·K⁻¹). After co-firing with a silicon wafer, the ceramic maintains its structural integrity, with no observable atomic diffusion at the ceramic-silicon interface, rendering it a potential candidate for advanced packaging and integration technologies.

Artificial adaptive soft infrared (IR) materials, mimicking the color-changing abilities observed in soft organisms such as cephalopods, hold significant promise in various emerging technologies, including unconventional flexible displays, intelligent camouflage systems, and advanced sensors. In this study, we integrated inherently deformable liquid metal (LM) microdroplets randomly into an elastomer matrix, creating a fully soft material that exhibits elastic compliance akin to soft biological tissue and adaptive IR-reflecting properties in response to compression. Under compressive strains, each LM inclusion behaves as a unit of dynamic IR reflector, transitioning between a contracted droplet with a corrugated surface and an expanded plate-like filler with a relatively smooth surface. These alterations in shape, size, and surface structure allow dynamic modulation of incident IR radiation's reflection, resulting in reversible changes in IR color (i.e., detected temperature). This mechanism replicates the dynamic alterations observed in cephalopod skin, where chromatophores dynamically manipulate visible light reflection by changing their size and morphology. We demonstrate proof-of-concept applications of this material, showing its ability to modify IR appearance through compression for visualization, with its localized color-change mechanism enabling its use as a tactile sensor in vision-based tactile grippers. These illustrate the potential of this material in emerging adaptive flexible electronics.

Dielectric ceramics are essential components in communication systems that operate within the microwave frequency range. In high-density packages, dielectric substrates ceramics must possess high thermal conductivity to efficiently dissipate heat. However, achieving adequate thermal conductivity (κ) in ceramics sintered at low temperatures is challenging. In this study, we employed the cold sintering process (CSP) to fabricate Li₂MoO₄-x%Al₂O₃ (0≤x ≤ 80, in volume) ceramics under 200 MPa pressure at 150 ℃. The Li₂MoO₄–40%Al₂O₃ composite exhibited significantly enhanced κ of 5.4 W·m⁻¹·K⁻¹, an 80% increase compared to pure Li₂MoO₄ ceramic with κ of 3 W·m⁻¹·K⁻¹. At 40% Al₂O₃ content, the Li₂MoO₄–Al₂O₃ ceramic demonstrated notable microwave properties (ε ~ 6.67, Q×f ~ 17,846 GHz, τ_f ~ −105 × 10⁻⁶ ℃^-1). Additionally, simulation of a microstrip patch antenna for 5 GHz applications using Li₂MoO₄–20%Al₂O₃ ceramic as dielectric substrate via Finite Element Simulation software showed excellent performance, with radiation efficiency exceeding 99% and low return loss (S₁₁ < −30 dB) at both 4.9 GHz and 28.0 GHz center frequencies. These findings underscore the suitability of Li₂MoO₄–Al₂O₃ ceramics for microwave dielectric substrate.

High-temperature polymer nanocomposites with high energy storage density (U_e) are promising dielectrics for capacitors used in electric vehicles, aerospace, etc. However, filler agglomeration and interface defects at high filler loadings significantly limit the enhancement of U_e and hamper the large-scale production of the nanocomposites. Here, polyetherimide (PEI) nanocomposites with nanoscale alumina (AO) at ultra-low contents were prepared via in situ polymerization from PEI monomers. We compared two composite dielectric preparation methods (in situ polymerization and ordinary solution blending) under the same conditions. In contrast to the nanocomposites obtained by blending PEI polymers with AO, the in situ nanocomposites exhibit substantially improved filler dispersion, together with largely suppressed conduction loss at high fields and high temperatures, leading to comprehensive enhancements of breakdown strength (E_b), charge-discharge efficiency (η) and U_e, simultaneously. The 0.3% (in volume) AO filled PEI nanocomposite film exhibits a superior U_e of 4.8 J/cm³ with η of 90% at 150 ℃, which is 128% and 218% higher than those of pristine PEI and the ex situ PEI/AO nanocomposite film under the same conditions, respectively. This work provides a scalable strategy for the preparation of dielectrics with both good processability and excellent high-temperature energy storage performance.

A series of high-k [(Na_0.5Bi_0.5)_xBi_1−x](W_xV_1−x)O₄ (abbreviated as NBWV(x value)) solid solution ceramics with a scheelite-like structure are synthesized by a modified solid-state reaction method at the temperature range of 680–760 ℃. A monoclinic (0 ≤ x < 0.09) to tetragonal scheelite (0.09 ≤ x ≤ 1.0) structural phase transition is confirmed by X-ray diffraction (XRD), Raman, and infrared (IR) analyses. The effect of structural deformation and order–disorder caused by Na⁺/Bi³⁺/W⁶⁺ complex substitution on microwave dielectric properties is investigated in detail. The compositional series possess a wide range of variable relative permittivity (ε_r = 24.8–80) and temperature coefficient of resonant frequency (TCF value, −271.9–188.9 ppm/℃). The maximum permittivity of 80 and a high Q×f value of ~10,000 GHz are obtained near the phase boundary at x = 0.09. Furthermore, the temperature-stable dielectric ceramics sintered at 680 ℃ with excellent microwave dielectric properties of ε_r = 80.7, Q×f = 9400 GHz (at 4.1 GHz), and TCF value = −3.8 ppm/℃ are designed by mixing the components of x = 0.07 and 0.08. In summary, similar sinterability and structural compatibility of scheelite-like solid solution systems make it potential for low-temperature co-fired ceramic (LTCC) applications.

Although many dielectric polymers exhibit high energy storage density (U_e) with enhanced dipolar polarization at room temperature, the substantially increased electric conduction loss at high applied electric fields and high temperatures remains a great challenge. Here, we report a strategy that high contents of medium-polar ester group and end-group (St) modification are introduced into a biodegradable polymer polylactic acid (PLA) to synergistically reduce the loss and enhance U_e and charge-discharge efficiency (η). The resultant St-modified PLA polymer (PLA-St) exhibits an U_e of 6.5 J/cm³ with an ultra-high η (95.4%), far outperforming the best reported dielectric polymers. It is worth noting that the modified molecular structures can generate deep trap centers and restrict the local dipole motions in the polymer, which are responsible for the reduction of conduction loss and improvements in high-temperature capacitive performance. In addition, the PLA-St polymer shows intrinsically excellent self-healing ability and cyclic stability surviving over 500 000 charge-discharge cycles. This work offers an efficient route to next-generation eco-friendly dielectric polymers with high energy density, low loss, and long-term stability.

Multi-band microwave absorption is becoming ubiquitous owing to the increasingly complex electromagnetic environment driven by the diversity of electronic devices. However, research on efficient electromagnetic absorbers applicable in both centimeter-wave and millimeter-wave bands to address the electromagnetic interference in 5G networks is highly challenging. In this study, Fe_x(Co_yNi_1-x)_100-x particles with two phases (face-centered cubic (FCC) and hexagonal close-packed (HCP)) were synthesized and were found to exhibit excellent electromagnetic wave absorption. HCP phase with high magnetocrystalline anisotropy was introduced into FCC phase Fe_x(Co_yNi_1-x)_100-x, resulting in natural resonances in multi-band frequency. Prominent microwave absorption properties in ultra-wide bandwidth ranging from 6.9 to 39.5 GHz were obtained. The maximum reflection loss (R_L) of the Fe₂₃(Co_0.5Ni_0.5)₇₇ composite film reached −50 dB. Such a remarkable absorption performance is attributed to the synergetic effects of the multiple natural resonances generated by the coexistence of HCP and FCC phases in Fe₂₃(Co_0.5Ni_0.5)₇₇. Overall, this work is promising for the future design of high-performance microwave absorbing materials in a wide bandwidth.

In this work, oxygen vacancy-regulated La_0.7Ca_0.3MnO_3-δ: Ag (LCMO: A) nanocomposite thin films on LaAlO₃ (001) substrates were investigated to obtain films with large temperature coefficient of resistance (TCR) values. LCMO: A nanocomposite thin films were synthesized using pulsed laser deposition, and oxygen pressures during film deposition and annealing steps were optimized. As oxygen pressures increased, lattice parameter increased from 70 Pa to 100 Pa, T_p increased monotonically from 168 K to 282 K, and average Mn⁴⁺ concentration in the film increased as indicated by X-ray photoemission spectroscopy data. Record high TCR value of ~37% K⁻¹ was achieved in LCMO: A nanocomposite thin film prepared with optimal oxygen pressures, making this film promising candidate for applications in bolometers.

In this work, the (1-x)CaWO₄-xNa₂WO₄ (x = 0.1, 0.2, denoted as 0.9CW-0.1NW and 0.8CW-0.2NW, respectively) ultralow-loss microwave dielectric ceramics were prepared via solid-state reaction method. Using low melting-point Na₂WO₄ as sintering aid to prepare CaWO₄Na₂WO₄ composite ceramics, the sintering temperature of CaWO₄ was successfully reduced while maintaining excellent microwave performance. The optimal microwave dielectric properties have been achieved at 900 °C for 0.9CW-0.1NW ceramic: ε_r = 9.0, Q × f = 105660 GHz, tanδ = 1.1 × 10⁻⁴ and τ_f = −35.4 ppm/°C at a frequency of 12.0 GHz. For the 0.8CW-0.2NW ceramic, the optimal microwave dielectric properties have been obtained at 740 °C, with ε_r = 8.5, Q × f = 97014 GHz, tanδ = 1.2 × 10⁻⁴ and τ_f = −37.4 ppm/°C at a frequency of 11.8 GHz. In summary, both composite ceramics exhibit low sintering temperatures, excellent dielectric properties and chemical compatibility with the Ag electrode. The findings of this study provide an effective approach to prepare novel composite ceramics as promising candidates for LTCC applications.