Materials science researchers have reported the discovery of materials that totally defy the laws of chemistry.
In 1954, Linus Pauling was awarded the Nobel Prize in Chemistry for setting a scientific rule regarding the formation of chemical bonds that has held firm for decades. According to his findings, the fragments of the atomic lattice in inorganic materials are connected by ‘vertices’ rather than faces.
Pauling claimed that bonding by faces is so energy-intensive that it simply could not exist in nature. However, new findings published to Nature Communications by an international team of researchers from Russia, Germany, Sweden and the US reveal two materials that completely shatter this rule.
The researchers demonstrated these ‘impossible’ modifications to silica coesite-IV and coesite-V. After proving it could be done theoretically using a Russian supercomputer and running subsequent experiments, the team showed it is possible to form bonding by faces when the materials are forged in ultra-high-pressure conditions.
Within high-pressure environments, scientists have found that a special modification of silicon oxide, polymorph-coesite, undergoes a number of phase transitions at a pressure of 30 gigapascals (GPa). This leads to the formation of coesite-IV and coesite-V which maintain tetrahedrons SiO4 as the main structural elements of the crystal lattice.
These new experiments have taken this further, compressing silicon oxide in a diamond anvil to a pressure of more than 30 GPa. The resulting structural changes in this phase – observed using single-crystal x-ray diffraction – reveal surprising changes that are exceptions to Pauling’s rules.
The discovery reveals two completely new modifications of coesite-IV and coesite-V that have pentacoordinated silicon, adjacent octahedrons SiO6, and consist of four, five and six-coordinated silicon at the same time. These structures defy the classical view of crystal chemistry and several fragments of the atomic lattice indeed connect by faces, not vertices.
Changes development of materials science
“Two newly discovered coesites contain octahedrons SiO6, that, contrary to Pauling’s rule, are connected through common face, which is the most energy-intensive for a chemical connection,” said Prof Igor Abrikosov, leader of the theoretical research team. “Our results show that the possible silicate magmas in the lower mantle of the Earth can have complex structures, which makes these magmas more compressible than predicted before.”
This discovery, the researchers said, completely changes the development of modern materials science, showing that fundamentally new classes of materials exist at extreme conditions. Recreating such conditions in the lab is now one of the most promising ways of creating new materials that could open up a whole new range of possibilities for researchers in the field.
Already, in one recent paper, scientists reported on the creation of nitrides that were once thought impossible to obtain. Such discoveries about the structure and mechanical properties of silicon oxide is vital to our understanding of the processes taking place in the mantle of our planet.
Updated, 15 November 2018 at 3.47pm: This article has been updated to include further detail on the newly discovered structures.