Incorrect Lattice parameter for Ge (space group I41/amd )

In Ge (space group I41/amd ) the lattice parameters are showing same i.e. a=b=c in materials project. however it is a tetragonal phase we know that a=b!=c should be the case. Kindly respond to the issue.

https://materialsproject.org/materials/mp-78/

Primitive unit cells and conventional standard cells can have different lattice constants and angles while describing the same structure. In this case, the primitive unit cell (1 atom per unit cell) being displayed is not tetragonal, but there is an equivalent tetragonal unit cell with the following structure and 4 atoms per unit cell.

a b c alpha beta gamma
5.18206 5.18206 2.87383 90.0000 90.0000 90.0000

Unit-cell volume = 77.173038 Å^3

Structure parameters

                   x          y          z          Occ.     B    Site      Sym.

1 Ge Ge0 0.50000 0.00000 0.75000 1.000 1.000 1a 1
2 Ge Ge1 0.00000 0.00000 0.50000 1.000 1.000 1a 1
3 Ge Ge2 0.00000 0.50000 0.25000 1.000 1.000 1a 1
4 Ge Ge3 0.50000 0.50000 0.00000 1.000 1.000 1a 1

1 Like

Welcome @Joyeta_Saha!

@jdagdelen’s answer is exactly right. On our new website, we show lattice parameters in their conventional setting by default to avoid confusion with the option to see primitive lattice parameters. For example, see the page for Ge (mp-78) here: mp-78: Ge (Tetragonal, I4_1/amd, 141)

Note also that many materials have multiple polymorphs available that may have different symmetries.

Best,

Matt