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Niobium triselenide is an inorganic compound belonging to the class of transition metal trichalcogenides. It has the formula NbSe3 and an oxidation state of +4. NbSe3 was first prepared by Meerschaut and Rouxel in 1975 and was the first reported one-dimensional compound to form a charge density wave sliding under an external electric field. Due to its many studies and exhibited phenomenas in quantum mechanics, niobium triselenide has become the model system for quasi-1-D charge density waves.

Structure
The monomer of this compound exhibits a six-coordinate geometry with six Se2-’s coordinating to one Nb center - NbSe66-. The selenides are the six vertices forming a triangular prism with two isosceles triangular faces and varying Se-Se triangular bond lengths of 2.37, 2.48, 2.91 Angstroms.

From Meerschaut and Rouxel’s crystal x-ray diffraction, NbSe3’s   monoclinic unit cell structure consists of six infinite chains of trigonal prisms stacked on top of the triangular sides and lined up parallely. Although the prisms share the same coordination, the six chains are not identical. Instead the cell consists of three chain types repeated twice where each chain is defined by its Se-Se bond length.

The high anisotropy of this structure results in the anisotropic crystallization of NbSe3, forming a ribbon-like fibre.

Electrical Conductivity and Charge Density Wave Formation
In the form of nanofibers, NbSe3 exhibits superconductivity under 2K.

The electrical resitivity of most metallic compounds decrease as temperature decreases. For the most part NbSe3 follows this trend except two anomalities exist where electrical resistivity reaches two local maximas at 145 K (-128oC) and 59 K (-214 oC). The maximas result in a sharp decrease in electrical conductivity. This observation is explained by the charge density wave formations that open the gaps in the Fermi surface.The opening causes the 1-D linear system to behave more like a semiconductor and less like a metal, a transition commonly known as Peierls transition. NbSe3 continues to be metallic despite going under the Peierls transition temperature because the charge density wave formation does not completely remove the Fermi surface, a phenomena known as imperfect Fermi surface nesting. .

Synthesis

 * Nb + 3Se → NbSe3

NbSe3 is prepared by traditional solid state reaction with niobium foil or niobium powder and selenium powder at 600 to 700oC in an inert and oxygen free atmosphere. The resulting black crystals can contain NbSe2 impurities which can be purified by chemical vapor transport (CVT) between 650 to 700oC. The lower limit of CVT was determined by the temperature in which NbSe2 is no longer stable.

Quantum Mechanics
NbSe3 had a significant role in providing evidence for charge density wave (CDW) transport, CDW pinning, magnestism, Shubnikov-de Hass oscillations, and the Aharonov-Bohm effect.

Possible Industrial Applications
Niobium triselenide is a cathode-of-interest for rechargeable lithium batteries due to its fibrous structure, high electrical conductivity, high gravimetric and volumetric energy densities at room temperature.