Highly Boron-Doped Graphite and Diamond Synthesized From Adamantane and Ortho-Carborane under High Pressure

TL;DR

This study demonstrates a high-pressure method to synthesize boron-doped graphite and diamond from adamantane and ortho-carborane, revealing boron's catalytic role and structural distribution in the materials.

Contribution

It introduces a novel high-pressure synthesis technique for boron-doped carbon allotropes using specific precursors, with detailed structural analysis and theoretical validation.

Findings

Boron doping enhances graphite quality at high temperatures.

Diamond synthesis occurs only above 7 GPa with boron incorporation.

Boron atoms are periodically distributed in graphite layers at high concentrations.

Abstract

This work demonstrates the effectiveness of the high-pressure method for the production of graphite and diamond with a high degree of boron doping using adamantanecarborane mixture as a precursor. At 8 GPa and $1700 ^{o}C$, graphite is obtained from adamantane $C_{10}H_{16}$, whereas microcrystals of boron-doped diamond (2{\div}2.5 at.% of boron) are synthesized from a mixture of adamantane and ortho-carborane $C_{2}B_{10}H_{12}$ (atomic ratio B:C = 5:95). This result shows convincingly the catalytical activity of boron in the synthesis of diamond under high pressure. At pressures lower than 7 GPa, only graphite is synthesized from the adamantane and carborane mixture. Graphitization starts at quite low temperatures (below $1400 ^{o}C$) and an increase in temperature simultaneously increases boron content and the quality of the graphite crystal lattice. Thorough study of the material structure allows us to assume that the substitutional boron atoms are distributed periodically and equidistantly from each other in the graphite layers at high boron concentrations (>1 at.%). The theoretical arguments and model ab initio calculations confirm this assumption and explain the experimentally observed boron concentrations.