Boron suboxide
Encyclopedia
Boron suboxide is a solid compound of boron
and oxygen
.
Its structure is built of eight icosahedra at the apexes of the rhombohedral unit cell (space group R3-m). Each icosahedron is composed of twelve boron
atoms. Two oxygen
atoms are located in the interstices along the [111] rhombohedral direction. Due to its short interatomic bond lengths and strongly covalent character, B6O displays a range of outstanding physical and chemical properties such as great hardness (close to that of diamond
, rhenium diboride
and boron nitride
), low mass density, high thermal conductivity, high chemical inertness, and excellent wear resistance.
B6O can be synthesized by reducing B2O3
with boron or by oxidation of boron with zinc oxide
or other oxidants. These boron suboxide materials formed at or near ambient pressure are generally oxygen deficient (B6Ox, x<0.9) and have poor crystallinity and very small grain size (less than 5 µm). High pressure applied during the synthesis of B6O can significantly increase the crystallinity, oxygen stoichiometry, and crystal size of the products. Mixtures of boron and B2O3
powders were usually used as starting materials in the reported methods for B6O synthesis.
Oxygen-deficient boron suboxide (B6Ox, x<0.9) might form icosahedral particles, which are neither single crystal
s nor quasicrystal
s, but twinned
groups of twenty tetrahedral crystals.
Boron
Boron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a metalloid. Because boron is not produced by stellar nucleosynthesis, it is a low-abundance element in both the solar system and the Earth's crust. However, boron is concentrated on Earth by the...
and oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
.
Its structure is built of eight icosahedra at the apexes of the rhombohedral unit cell (space group R3-m). Each icosahedron is composed of twelve boron
Boron
Boron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a metalloid. Because boron is not produced by stellar nucleosynthesis, it is a low-abundance element in both the solar system and the Earth's crust. However, boron is concentrated on Earth by the...
atoms. Two oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
atoms are located in the interstices along the [111] rhombohedral direction. Due to its short interatomic bond lengths and strongly covalent character, B6O displays a range of outstanding physical and chemical properties such as great hardness (close to that of diamond
Diamond
In mineralogy, diamond is an allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the conversion rate from diamond to graphite is negligible at ambient conditions...
, rhenium diboride
Rhenium diboride
Rhenium diboride is a synthetic superhard material. It was first synthesized in 1962 and re-emerged recently due to hopes of achieving high hardness comparable to that of diamond...
and boron nitride
Boron nitride
Boron nitride is a chemical compound with chemical formula BN, consisting of equal numbers of boron and nitrogen atoms. BN is isoelectronic to a similarly structured carbon lattice and thus exists in various crystalline forms...
), low mass density, high thermal conductivity, high chemical inertness, and excellent wear resistance.
B6O can be synthesized by reducing B2O3
Boron trioxide
Boron trioxide is one of the oxides of boron. It is a white, glassy solid with the formula B2O3. It is almost always found as the vitreous form; however, it can be crystallized after extensive annealing...
with boron or by oxidation of boron with zinc oxide
Zinc oxide
Zinc oxide is an inorganic compound with the formula ZnO. It is a white powder that is insoluble in water. The powder is widely used as an additive into numerous materials and products including plastics, ceramics, glass, cement, rubber , lubricants, paints, ointments, adhesives, sealants,...
or other oxidants. These boron suboxide materials formed at or near ambient pressure are generally oxygen deficient (B6Ox, x<0.9) and have poor crystallinity and very small grain size (less than 5 µm). High pressure applied during the synthesis of B6O can significantly increase the crystallinity, oxygen stoichiometry, and crystal size of the products. Mixtures of boron and B2O3
Boron trioxide
Boron trioxide is one of the oxides of boron. It is a white, glassy solid with the formula B2O3. It is almost always found as the vitreous form; however, it can be crystallized after extensive annealing...
powders were usually used as starting materials in the reported methods for B6O synthesis.
Oxygen-deficient boron suboxide (B6Ox, x<0.9) might form icosahedral particles, which are neither single crystal
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...
s nor quasicrystal
Quasicrystal
A quasiperiodic crystal, or, in short, quasicrystal, is a structure that is ordered but not periodic. A quasicrystalline pattern can continuously fill all available space, but it lacks translational symmetry...
s, but twinned
Crystal twinning
Crystal twinning occurs when two separate crystals share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals in a variety of specific configurations. A twin boundary or composition surface separates the two crystals....
groups of twenty tetrahedral crystals.
See also
- SuboxideSuboxideSuboxides are a class of oxides wherein the electropositive element is in excess relative to the “normal” oxides. When the electropositive element is a metal, the compounds are sometimes referred to as “metal-rich”. Thus the normal oxide of caesium is Cs2O, which is described as a Cs+ salt of O2−...
- Boron trioxideBoron trioxideBoron trioxide is one of the oxides of boron. It is a white, glassy solid with the formula B2O3. It is almost always found as the vitreous form; however, it can be crystallized after extensive annealing...
- Boron monoxideBoron monoxideBoron monoxide is a chemical compound of boron and oxygen. Two experimental studies have proposed existence of diamond-like and graphite-like B2O, as for boron nitride and carbon solids. However, a later, systematic, experimental study of boron oxide phase diagram suggests that B2O is unstable....
- HeterodiamondHeterodiamondHeterodiamond is a superhard material containing boron, carbon, and nitrogen . It is formed at high temperatures and high pressures, e.g., by application of an explosive shock wave to a mixture of diamond and cubic boron nitride. The heterodiamond is a polycrystalline material coagulated with...
- Beta carbon nitrideBeta carbon nitrideBeta carbon nitride is a material predicted to be harder than diamond.The material was first proposed in 1985 by Marvin Cohen and Amy Liu. Examining the nature of crystalline bonds they theorised that carbon and nitrogen atoms could form a particularly short and strong bond in a stable crystal...