#allotropes

Chemists synthesize a new allotrope of carbon

In a new study led by Oxford University's Department of Chemistry, chemists have demonstrated the synthesis of a cyclocarbon that is stable enough for spectroscopic characterization in solution at room temperature. The study is published in the journal Science. The synthesis of a new type of molecular carbon allotrope that can be studied under normal laboratory conditions is a rare achievement. The only previous example was the synthesis of fullerenes in 1990. In the new study, the molecule cyclo[48]carbon was synthesized as a catenane, i.e. with the C48 ring threaded through three other macrocycles. These threaded macrocycles increase the stability of C48 by preventing access to the protected cyclocarbon.

it feels really odd and spring like now that the clocks have gone forwards an hour, and now that means I have to wake up an hour earlier too logically

Covalent bonds found in alpha plutonium clarify its unusual atomic structure

Plutonium has captured the attention of scientists since its discovery in the early 1940s. This enigmatic element has an important role to play in emerging energy technologies like nuclear batteries and reactors, but it also has complicated electronic behavior that causes some intriguing effects. Its electron structure contributes to unconventional entropic properties at low temperatures, multiple phase transitions before melting, and complex bonding patterns. Although scientists are eager to explore these intriguing properties, studying plutonium remains notoriously difficult. Its strong electronic correlations, complex quantum effects like spin-orbit coupling, and changes due to radioactive decay make both experimental research and computer simulations challenging. To add further complexity, plutonium is also found in several different allotropes—forms of the same element with different atomic arrangements. Plutonium's alpha phase (α-Pu), for example, has a particularly complicated atomic structure. Understanding the complex bonding of this phase seemed like a worthwhile challenge for a newly formed collaboration of scientists to tackle.

Allotropy and Polymorphism

Polymorphism is defined as when a material has more than one potential crystal structure. These phase transformations can occur as a result of different external variables - temperature, pressure, etc. - but typically only refer to crystalline materials. (For example, glass is not a polymorph of silica, it is a metastable phase.) Allotropy is a similar concept, but applies only to pure elements. Carbon has multiple potential phase transformations, such as graphite to diamond (or vice versa), which are considered allotropes of the elements. Because of these definitions, polymorphic and allotropic phase transformations are typically solid-solid transformations.

On-surface synthesis of carbyne: An sp-hybridized linear carbon allotrope

In a study led by Prof. Wei Xu (Interdisciplinary Materials Research Center, School of Materials Science and Engineering, Tongji University) and published in the journal National Science Review, a research team achieved the successful synthesis of a one-dimensional carbon chain on the Au(111) surface, with the longest chain containing approximately 120 carbon atoms, and the polyynic nature of the carbon chain was unambiguously characterized by bond-resolved atomic force microscopy (AFM). The creation of new carbon forms with different topologies has emerged as an exciting topic in both fundamental chemistry and materials science. Carbyne (linear carbon chain), an elusive sp-hybridized linear carbon allotrope, has fascinated chemists and physicists for decades. Due to its high chemical reactivity and extreme instability, carbyne was much less explored.

Study identifies a new synthesis technique to attain monolayer honeycomb SiC

Silicon carbide (SiC) is a hard crystalline compound of silicon and carbon that rarely occurs in nature and is generally synthetically produced. In addition to being used to create ceramic plates, bulletproof vests and other commercial products, SiC is a semiconductor, a material that has a moderate electrical conductivity, ranging between that of conductors and insulators.

Physicists and material scientists have been investigating the properties of this semiconductor for decades. Like other materials, SiC can exist in different physical forms (i.e., allotropes), and its 2D allotrope has so far remained elusive and primarily hypothesized.

According to theoretical predictions, the 2D allotrope of this semiconductor would have a large direct band gap of 2.5 eV and a high chemical versability, and would be stable in ambient conditions. So far, however, this was not empirically verified, as existing studies only reported disordered nanoflakes of 2D SiC.