High temperature dielectric loss of h-BN at X band and its dependence on the electron structure, defects and impurities

The dielectric loss of hexagonal boron nitride (h-BN) at high temperature ranging from 291 K to 2023 K at X band is investigated by experimental and theoretical analyses. The dielectric loss is relatively low below 1273 K, nevertheless, above this temperature, much rapid increase in the dielectric loss is observed with the increase of temperature. At 2023 K, the dielectric loss is found to be 40 times more than that at room temperature. Our calculation reveals that the rapid increase in the dielectric loss from 1273 K to 1800 K is mainly contributed by the boron vacancy (VB) defects but from that 1800 K to 2023 K is mostly caused by the hopping phenomenon of the electrons. It is also found that the reason that VB has the smallest energy among the defect is that its electronegativiities are smaller and its bonding ability is weaker compared to other defects. And the co-existence of defects and impurities is found to enhance the conduction loss by first principle calculations, which is due to that the bond of B∗ atom and N∗ atom becomes weak and the jumping distance of the impurity ions is increased when VB and Na co-doped in the structure.

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