Synthesize B-Doped Diamond Using Graphite Intercalation Compounds

The conductivity and thermo-stability of diamond with boron doping could be improved. In this paper, a new method was presented that B-doped diamond was synthesized at high pressure and high temperature (HTHP) using B-doped graphite intercalation compounds (GICs).Using H3BO3, NH4BF4 and KBH4 as intercalant, GICs had been prepared by melt-salt in vacuum, melt-salt in vacuum infiltration, enhancing pressure melt-salt, and electrolyte intercalation. Structure of GICs had been analyzed by XRD, and stability of GICs had been studied. Diamond was synthesized using B-doped GICs as carbon sources by HTHP method. Morphology of B-doped diamond had been observed by SEM. Boron contents and impurity situation of B-doped diamond had been analyzed by FTIR/Raman and XRF. DTA curves of B-doped diamond had been studied, and the resistances had been measured.The experimental results showed that H3BO3-GICs, NH4BF4-GICs and KBH4-GICs had been prepared successfully by melt-salt in vacuum, melt-salt in vacuum infiltration, enhancing pressure melt-salt, and electrolyte intercalation. GICs had mixed stage. Stage number of GICs decreased with intercalation duration prolonging. It is unstable when GICs was washed, and H3BO3-GICs was hydrolyzed. B-doped diamonds were obtained under the condition of 1250℃~1350℃ and 5GPa~6GPa. Color of diamond became deep with boron contents increasing, till becoming black. B-doped diamond was polycrystalline, and crystal surface was developed incompletely. It was found by FTIR that boron existed as substitute atom or interstitial atom. Boron contents of diamond changed from 5 ppm to 2158 ppm. Conductivity and thermo-stability of B-doped diamond increased with boron contents increasing. Anti-oxidation temperature of diamond with 500 ppm boron reached 1070 ℃ Specific resistance of diamond with 2158 ppm boron was 1.93 Ω cm.