Rapid liquid phase–assisted ultrahigh-temperature sintering of high-entropy ceramic composites

Abstract

High-entropy ceramics and their composites display high mechanical strength and attractive high-temperature stabilities. However, properties like strong covalent bond character and low self-diffusion coefficients make them difficult to get sintered, limiting their mass popularity. Here, we present a rapid liquid phase–assisted ultrahigh-temperature sintering strategy and use high-entropy metal diboride/boron carbide composite as a proof of concept. We use a carbon-based heater to fast-heat the composite to around 3000 K, and a small fraction of eutectic liquid was formed at the interface between high-entropy metal diborides and boron carbide. A crystalline dodecaboride intergranular phase was generated upon cooling to ameliorate the adhesion between the components. The as-sintered composite presents a high hardness of 36.4 GPa at a load of 0.49 N and 24.4 GPa at a load of 9.8 N. This liquid phase–assisted rapid ultrahigh-temperature strategy can be widely applicable for other ultrahigh-temperature ceramics as well.

Giant Energy Storage Density with Antiferroelectric‐Like Properties in BNT‐Based Ceramics via Phase Structure Engineering

“…In the overdamping test, a 150 Ω resistor is applied and the discharge current waveform of BNST-CLT is shown in Figure 6c. According to this, the discharge energy storage density W d could be derived from the following equation [53] W d = R ∫ I(t) 2 dt∕V (6) in which R stands for the applied resistance of 150 Ω, and I, t denotes the discharge current as well as time, correspondingly. The W d achieves 1.01 J cm −3 at an electric field of 200 kV cm −1 (Figure 7d), which is closely in line with the ferroelectric test results.…”

“…[4,5] Superior to others, ceramic capacitors represent the mainstream choice since there are the advantages of superior dielectric properties along with high temperature resistance. [6] However, the restricted energy storage density of dielectric capacitors compared to electrochemical capacitors constrains the further adoption. [2,7] Enhancing the energy storage performance of dielectric capacitors has emerged as a current research priority.…”

“…[8][9] Ferroelectric materials where there is spontaneous polarization flipping with the electric field are a specialized class in dielectric materials. [6] Microscopically, the ferroelectric domain structures with the same direction of spontaneous polarization are commonly established. Initial research focused on Pb-based energy storage ceramics which is attributed to that the 6s of Pb ions and the 2p of O ions orbital hybridization favors highly maximum polarization.…”

One-Dimensional High-Entropy Compounds

“…High-entropy compounds (HECs) have gained extensive attention in recent years due to their unconventional structures and remarkable physicochemical properties. − Typically composed of five or more near-equimolar principal metal cations within a solid-solution phase, HECs exhibit a high degree of disorder in their atomic arrangements, resulting in increased configurational entropy. − Consequently, it becomes difficult to regulate the structure and morphology of HECs during their synthesis, particularly when their size is reduced to the nanoscale or even smaller, such as the subnanoscale. − …”

Synthesis of Ultrathin High-Entropy Oxides with Phase Controllability

“…The decrease of energy thermodynamically is beneficial to overcoming elemental immiscibility to form a high-entropy state. ,− Recently, we reported that utilizing Ga with relatively negative mixing enthalpy to reduce Gibbs free energy can realize uniform elemental mixing in high-entropy alloys under relatively mild reaction conditions . Therefore, it provides an idea to construct a high-entropy mixing state in oxides.…”