Related Experiment Video
Updated: May 18, 2026
07:12
Design of a Cyclic Pressure Bioreactor for the Ex Vivo Study of Aortic Heart Valves
Published on: August 23, 2011
Pressure-driven evolution of the covalent network in CaB6.
A N Kolmogorov1, S Shah, E R Margine
1Department of Materials, University of Oxford, United Kingdom.
Physical Review Letters
|September 26, 2012
Summary
Calcium hexaboride (CaB6) crystal structure transforms under high pressure. A new tetragonal phase with complex boron units was discovered and stabilized at ambient pressure.
Area of Science:
- Materials Science
- Solid-State Chemistry
- Crystallography
Background:
- Calcium hexaboride (CaB6) belongs to the metal hexaboride family.
- The known CaB6 structure is a simple cubic cP7 type, established over 80 years ago.
Purpose of the Study:
- To investigate the crystal structure of CaB6 under high pressure and temperature conditions.
- To characterize novel structural phases of CaB6 beyond the known cubic form.
Main Methods:
- High-pressure and high-temperature synthesis of CaB6.
- X-ray diffraction for structural analysis.
- Ab initio evolutionary search for structure determination.
Main Results:
- CaB6 undergoes a structural transformation under pressures up to 44 GPa.
- A new tetragonal tI56 phase of CaB6 was identified.
- This phase features complex 24-atom boron units and 28 atoms per primitive unit cell.
- The novel CaB6 phase was successfully quenched to ambient pressure.
Conclusions:
- The simple cubic structure of CaB6 is not stable under high pressure.
- A complex tetragonal CaB6 phase emerges, challenging previous structural understanding.
- The discovery opens new avenues for exploring metal hexaboride structures and properties.
Related Concept Videos
02:18Network Covalent Solids
Network covalent solids contain a three-dimensional network of covalently bonded atoms as found in the crystal structures of nonmetals like diamond, graphite, silicon, and some covalent compounds, such as silicon dioxide (sand) and silicon carbide (carborundum, the abrasive on sandpaper). Many minerals have networks of covalent bonds.
To break or to melt a covalent network solid, covalent bonds must be broken. Because covalent bonds are relatively strong, covalent network solids are typically...
To break or to melt a covalent network solid, covalent bonds must be broken. Because covalent bonds are relatively strong, covalent network solids are typically...
02:32Bonding in Metals
Metallic bonds are formed between two metal atoms. A simplified model to describe metallic bonding has been developed by Paul Drüde called the “Electron Sea Model”.
02:48Ionic Bonding and Electron Transfer
Ions are atoms or molecules bearing an electrical charge. A cation (a positive ion) forms when a neutral atom loses one or more electrons from its valence shell, and an anion (a negative ion) forms when a neutral atom gains one or more electrons in its valence shell. Compounds composed of ions are called ionic compounds (or salts), and their constituent ions are held together by ionic bonds: electrostatic forces of attraction between oppositely charged cations and anions.
01:29Covalent Bonds
Overview
01:08Covalent Bonds
Overview
When two atoms share electrons to complete their valence shells, they create a covalent bond. An atom's electronegativity—the force with which shared electrons are pulled towards an atom—determines how the electrons are shared. Molecules formed with covalent bonds can be either polar or nonpolar. Atoms with similar electronegativities form nonpolar covalent bonds; the electrons are shared equally. Atoms with different electronegativities share electrons unequally, creating polar bonds.
When two atoms share electrons to complete their valence shells, they create a covalent bond. An atom's electronegativity—the force with which shared electrons are pulled towards an atom—determines how the electrons are shared. Molecules formed with covalent bonds can be either polar or nonpolar. Atoms with similar electronegativities form nonpolar covalent bonds; the electrons are shared equally. Atoms with different electronegativities share electrons unequally, creating polar bonds.
01:30ATP Driven Pumps III: V-type Pumps
V-type pumps are ATP-driven pumps found in the vacuolar membranes of plants, yeast, endosomal and lysosomal membranes of animal cells, plasma membranes of a few specialized eukaryotic cells, and some prokaryotes. They are also known as the V1Vo-ATPase, that couple ATP hydrolysis to transport protons against a concentration gradient.
The peripheral or cytosolic V1 domain with eight subunits is involved in ATP hydrolysis. The integral or transmembrane V0 domain containing at least five subunits...
The peripheral or cytosolic V1 domain with eight subunits is involved in ATP hydrolysis. The integral or transmembrane V0 domain containing at least five subunits...