In this study, a purity of up to 98.36 wt. % GdB 6 with screw dislocation growth morphology were successfully fabricated using an in-situ reaction approach. The terraced-like structure of the GdB 6 enhanced the interfacial polarization and multiple interface scattering of the electromagnetic waves. As a result, the as-obtained high purity GdB 6 powder presented superior electromagnetic wave absorption performance. The minimum reflection loss value can be −49.24 dB at the frequency of 13.12 GHz with a thin matching thickness of 1.44 mm. In addition, the widest effective absorption bandwidth can be up to ∼4 GHz (14–18 GHz) with a thin matching thickness of 1.25 mm. The remarkable electromagnetic wave absorption performance of GdB 6 ceramics could be attributed to conductance loss and polarization loss enhanced by the screw dislocation growth defects, as well as synergistic effects with magnetic loss. The as-obtained GdB 6 with synergistic dielectric loss and magnetic loss is to be a novel single-phase with excellent electromagnetic wave absorbing material, which will pave the way on the investigation of rare earth hexaborides for the ultra-high temperature environment applications.
In this study, a highly dense GdB 6 bulk ceramic material was fabricated using one-step in-situ reaction spark plasma sintering technology. The sample with a relative density of 96.7 % and a purity of 96.9 wt% was successfully obtained by sintering at 1800 °C for 30 min under a uniaxial pressure of 50 MPa. The Vickers hardness , elastic modulus and fracture toughness of the as-obtained GdB 6 bulk ceramics were 18.9 GPa, 209 GPa and 1.6 MPa·m 1/2 , respectively. The thermal conductivity of GdB 6 at room temperature was 28.68 W·m −1 ·K −1 , 70 % of which was mainly attributed to phonon vibration, while the remaining 30 % to the electrical thermal conductivity. In addition, the as-obtained GdB 6 ceramics showed no phase transformation after heat treatment at a relatively high temperature of 2100 °C for 20 min in Ar atmosphere. The highly covalent octahedral boron framework played a critical role in maintaining the phase stability of the GdB 6 crystal lattice . This suggested that GdB 6 ceramics could be used as potential ultra-high temperature ceramics for aerospace applications and high-power vacuum electronic devices operated at high temperatures.
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