Synthesis and electrical conductivity of Na3B20

Abstract Na3B20 powder was prepared by heating amorphous B and Na in a BN crucible at 1173–1373 K. Na2B29, which was formed from Na3B20, was contained in the products obtained at and above 1453 K. Black square plate-like Na3B20 single crystals with a size of approximately 40–100 μm were grown by heating crystalline B and Na at 1223 K for 48 h. Na3B20 was relatively unstable against the moisture in air, and gradually converted into H3BO3. A polycrystalline bulk Na3B20 sample with a relative density of 73.4% was obtained by heating a compact of ball-milled amorphous B powder in Na vapor at 1223 K for 24 h. The electrical conductivity of the bulk sample was 1.15 × 106 S/m at 295 K.