Nanoindentation hardness of hot-pressed boron suboxide

Cyclic formation of boron suboxide crystallites into star-shaped nanoplates

“…Since B 6 O was first proved to exist half a century ago [1] it has been studied intensively, and is renowned for its extremely high hardness. One of the first studies, by Badzian [2], demonstrated the ability of B 6 O to scratch the hardest (111) crystallographic plane of natural diamond. He et al [3] reported that single-crystal B 6 O had a high hardness of 45 GPa, which was comparable to that of cubic boron nitride.…”

“…One of the first studies, by Badzian [2], demonstrated the ability of B 6 O to scratch the hardest (111) crystallographic plane of natural diamond. He et al [3] reported that single-crystal B 6 O had a high hardness of 45 GPa, which was comparable to that of cubic boron nitride. As well as possessing such high hardness, B 6 O can be synthesized at the relatively low temperature of 1400°C in an ambient pressure environment, making it one of the easiest superhard materials to produce, especially in comparison to diamond and cubic boron nitride.…”

“…As well as possessing such high hardness, B 6 O can be synthesized at the relatively low temperature of 1400°C in an ambient pressure environment, making it one of the easiest superhard materials to produce, especially in comparison to diamond and cubic boron nitride. Despite the many advantages of B 6 O, production of the material is still plagued by a number of problems, such as difficulty in synthesizing stoichiometrically balanced B 6 O, poor crystallinity, poor sinterability and a bulk reaction product that requires further milling [3][4][5][6]. Similar to other boron-rich solids [5], many properties of B 6 O remain poorly understood.…”

“…Despite the many advantages of B 6 O, production of the material is still plagued by a number of problems, such as difficulty in synthesizing stoichiometrically balanced B 6 O, poor crystallinity, poor sinterability and a bulk reaction product that requires further milling [3][4][5][6]. Similar to other boron-rich solids [5], many properties of B 6 O remain poorly understood.…”

“…Different nanostructural forms of B 6 O have also been widely synthesized and studied by many material researchers, such as nanowires [8], nanoplatelets [9] and nanofilms [10,11]. Probably the most remarkable structure is icosahedral particles of boron suboxide.…”