Ever had your phone heat up in your hand? Scientists are exploring materials whose electronic properties could reduce the amount of resistive heating created by the transistors in computer chips. These new materials incorporate a one-dimensional electronic structure—meaning that the electrons which create current are confined to a single dimension—inside a three-dimensional crystal with insulating properties.
It isn’t straightforward, however, to synthesize a material with true one-dimensional conductive components and no electronic interactions in the other dimensions. Recent research results by a team whose members collaborate from universities in Spain, Germany and the United States propose and evaluate the chemical criteria required to synthesize such a material and demonstrate the ability of a bulk crystal (BiIr4Se8) fabricated according to such criteria to produce one-dimensional electronic structure.
The team reasoned that such a bulk crystal would need to have the following three characteristics. First, the material would need to include a one-dimensional conductive component and an insulating component which physically surrounds the conductive one. Second, the atoms of the conductive component would need to have charged particles available in their outermost electron shell so those particles could move and produce a current. Lastly, the insulating and conductive components must have no electronic interactions; this is most easily accomplished by choosing components which do not form covalent bonds.
Previously published literature on this topic explored a crystal structure (called “hollandite”) that consists of octahedral tunnels formed by one compound (termed the scaffolding) surrounding a second compound whose shape is linear (called the chain). The team decided to use a variant of the hollandite structure that consists of scaffolding made from iridium hexaselenium (IrSe6) and chains of bismuth atoms; the bulk crystal structure is BiIr4Se8.
To characterize the physical and electronic structure of the BiIr4Se8 bulk crystal, the team performed multiple types of examination. They used previously published high-symmetry structures to perform electron counting, which assigns valence electrons to the atoms which make up the crystal’s unit cell; this exercise told them the bismuth atoms have an unpaired single electron in their outer orbital, which would require stabilization. Stabilization would most likely occur through bonding between bismuth atoms. The team applied density functional theory—which predicts a material’s electronic behavior based on quantum mechanics—to calculate that the crystal would contain a conductive component (a metallic band) and that component was concentrated around the bismuth chain.
Read more on Argonne website