Introduction to Zintl phases

Zintl phases are valence-balanced semiconductors, where typically electropositive group 1 or 2 elements donate electrons to more electronegative group 13-16 elements.

For example, in NaSi (Na4Si4, see Figure 1), the electronic situation can be described as follows:

  • Each Na atom donates 1e–.
  • Each Si atom accepts 1e–
  • [Si4]4– tetrahedra are isoelectronic with P4 tetrahedra (white phosphorus)

As a result, there is covalent bonding within the Si tetrahedra and ionic bonding between the anionic polyhedra and the cations. Basically, the electron transfer in this case follows the well-known 8-electron rule. Ideally, Zintl phases should be semiconductors. 

Figure 1. Na4Si4 (C2/c) with [Si4]4– tetrahedra (blue) and Na+ cations (violet).

Examples of Zintl phases

Silicon

Germanium

Other



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