The design and fabrication of novel hard materials with excellent electrical conductivity is attractive in scientific and technological application under extreme conditions. Metal borides have brought substantial interest for decades in material science because of their strong covalent BB bonding network for intrinsic incompressibility and MM bonding for electron transportation. Here the successful synthesis of a novel hard alkali metal boride as NaB4 with high thermal stability (873 K) and metallic behaviors is reported. The relatively low synthetic P/T conditions (lowest at 1.5 GPa and 1000 K) enable the easy fabrication of large bulk materials (several centimeters in diameter). The studies reveal that the Vickers hardness value of NaB4 can reach up to 26 GPa, associated with superior incompressibility along (001) direction of honeycomb‐like boron structure that exhibits the highest shear modulus up to 96 GPa for borides. The NaB4 structure undergoes an interesting metallic‐semiconducting transition under compression up to 61 GPa. This new form of hard metal boride material with pressure‐tunable electrical properties enables the development of industrial applications as future electrical devices.
Conventional hard and superhard materials, such as diamond and cubic boron nitride, are attractive for fundamental material science and practical industrial application, but severely limited by their poor electrical conductivity. Therefore, it is desirable to design and fabricate novel materials for superior hardness and conductivity. Herein, a class of hard superconductors in alkali or alkaline‐earth metal (AM) borides, namely AMB7, constituted by a B23 cage with one centered metal atom (Li, Na, K, Mg, Ca, and Sr) is reported, which is the first stable clathrate structure in AMB systems. The theoretical calculations demonstrate that all these pressure‐stabilized clathrate structures can be quenched down to ambient conditions, which provides an essential prerequisite for experimental synthesis at moderate pressures. Among them, the highest hardness and maximum superconducting transition temperature (Tc) value are achieved in SrB7 (25.1 GPa) and MgB7 (29.3 K), respectively. Interestingly, the results show that KB7 simultaneously behaves high hardness (22.5 GPa) and superconducting transition temperature (Tc ≈26.2 K). This study opens up a new way to search and design novel superconductors with favorable mechanical properties under high pressure and high‐temperature conditions.
Research of vortex properties in type-II superconductors is of great importance for potential applications and fundamental physics. Here, we present a comprehensive study of the critical current density J
c, vortex pinning, and phase diagram of NaCl-type InTe1-x
Se
x
(x = 0, 0.1, 0.2) superconductors synthesized by high-pressure technique. Our studies reveal that the values of J
c calculated by the Bean model exceed 104 A/cm2 in the InTe1-x
Se
x
system, signifying good potential for applications. The magnetic hysteresis loops (MHLs) show an asymmetric characteristic at various degrees, which is associated with the surface barrier. Intriguingly, a rare phenomenon in which the second magnetization peak in the MHLs occurs only in the field-descending branch is detected in InTe0.9Se0.1. Such an anomalous behavior has not been observed previously and can be described by considering the respective roles of the surface barrier and bulk pinning in the field-ascending and field-descending branches. By analyzing the pinning force density versus reduced field, the pinning mechanisms are studied in detail in the framework of Dew-Hughes model. Finally, combining the results of resistivity and magnetization measurements, the vortex phase diagrams are constructed and discussed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.