Tetragonal

It forms four major polymorphs : α-rhombohedral and β-rhombohedral (α-R and β-R), γ and β-tetragonal (β-T); α-tetragonal phase also exists (α-T), but is very difficult to produce without significant contamination.

This difference is caused by nickel and iron having a similar size but different interatomic magnetic and quantum interactions. citation Tetragonal phase There is evidence of a tetragonal phase, observed in X-ray powder tests and later under a microscope.

Applying higher pressure of the order of hundreds or thousands of kilobars induces a series of phase transformations, in particular with a tetragonal phase appearing at about 900 kbar.

At room temperature, protactinium crystallizes in body-centered tetragonal structure which can be regarded as distorted body-centered cubic lattice; this structure does not change upon compression up to 53 GPa.

Below 0.2% carbon, it takes on a ferrite BCC crystal form, but at higher carbon content it takes a body-centered tetragonal (BCT) structure.

In monoclinic, rhombohedral, tetragonal, and trigonal/hexagonal systems there is one unique axis (sometimes called the principal axis) which has higher rotational symmetry than the other two axes.

Recent research showed that only some crystalline facets of tetragonal (beta) Sn are responsible for undesirable electrochemical activity. citation Precautions main Cases of poisoning from tin metal, its oxides, and its salts are almost unknown.

The alloy has a tetragonal structure with a superconductivity transition temperature of −268.3 °C (4.9 K).

The thermal expansion coefficient of the tetragonal phase between room temperature and 700 °C is 9.9 /°C.

This property also applies for tetragonal disphenoids when applied to the two special edge pairs.

Thorite, or tetragonal thorium silicate (ThSiO 4 ), also has a high thorium content and is the mineral in which thorium was first discovered.

When tested two meteorites gave d-values that could “be indexed on the basis of a tetragonal unit cell, but not on the basis of a cubic or hexagonal unit cell”. citation It has been speculated to be e-iron, a hexagonal polymorph of iron.