A15 phases

The A15 phases (also known as β-W or Cr₃Si structure types) are series of intermetallic compounds with the chemical formula A₃B (where A is a transition metal and B can be any element) and a specific structure. Many of these compounds have superconductivity at around 20 K (−424 °F), which is comparatively high, and remain superconductive in magnetic fields of tens of teslas (hundreds of kilogauss). This kind of superconductivity (Type-II superconductivity) is an important area of study as it has several practical applications.

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Properties

The all materials in the A15 phase are very brittle which makes machining difficult for those materials.

Structure

The structure of the A₃B is based on a bcc structure of B. It has one lattice point in the centre of the unit cell in addition to the eight corner points. It has a net total of 2 lattice points per unit cell. Two atoms A are located on the each cube face is bisectedby orthogonal Nb chains

Pm3n-O<sub>h</sub>

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History

The first time the A15 structure was observed in 1931 when a electrolytically deposited layer of tungsten was examined. The discussion if the β–tungsten structure is an allotrope of tungsten or a the structure of a tungsten suboxide was long-standing and in 1998 still articles about the discussion were published. In the end it seems most...
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