The atoms of metals are organized in ordered structures denominated crystal lattices. The geometry of the latter depends of the nature of the material as well as of temperature and pressure. At room temperature and atmospheric pressure, pure metals like gold, aluminium and copper have cubic lattices, and others like magnesium, titanium and zirconium have hexagonal structures (called alpha phases, a).
Increases in pressure occasionally cause changes in the geometry of the crystal lattice, resulting in the appearance of new phases. For example, in the case of titanium, the hexagonal a lattice, stable at 1 atm, transforms into a cubic structure (beta phase) when a hydrostatic pressure of approximately 1 million atmospheres is applied. If, once the cubic phase has been generated, the pressure is reduced down to 1 atm, the reverse transformation takes place, giving rise to the original hexagonal a phase. Due to the extreme pressure conditions needed to generate these new phases, the practical applications of these materials are very limited.