What is the Difference Between Spinel and Inverse Spinel Structure?
🆚 Go to Comparative Table 🆚The main difference between spinel and inverse spinel structures lies in the distribution of cations in their crystal lattices:
- Spinel structure: In this structure, A cations occupy 1/8th of the tetrahedral sites, while B cations occupy half of the octahedral sites. The general formula for a spinel structure is A[subscript{8}][A[subscript{16}]O[subscript{32}].
- Inverse spinel structure: In this structure, all A cations and half of the B cations occupy octahedral sites, while the other half of the B cations occupy tetrahedral sites. The general formula for an inverse spinel structure is B[subscript{1/2}[A[subscript{1/4}][B[subscript{1/4]]O[subscript{4].
Inverse spinel structures are formed when the divalent A[superscript{II}] ion has a comparatively more favorable crystal field stabilization energy (CFSE) gain in octahedral geometry than the trivalent B[superscript{III}] ion. The choice of the normal or inverse spinel structure is primarily driven by the CFSE of the transition metal ions.
Examples of spinel and inverse spinel structures include:
- Normal spinel: MgAl[superscript{2+}]Osubscript{4.
- Inverse spinel: Fe[superscript{3+}]Osubscript{4.
Intermediate cases between normal and inverse spinel structures also exist, where the cation distribution can be described as (A[subscript{1-x}][B[subscript{x}][A[subscript{x/2}][B[subscript{1-x/2]][O[subscript{4].
Comparative Table: Spinel vs Inverse Spinel Structure
The key difference between spinel and inverse spinel structures lies in the arrangement of cations in their unit cells. Here is a comparison of the two structures:
Spinel Structure | Inverse Spinel Structure |
---|---|
A ions occupy 1/8th of the tetrahedral holes, and B ions occupy half of the octahedral holes. | All A cations and half of the B cations occupy octahedral sites, and the other half of B cations occupy tetrahedral sites. |
Spinel structures have a close-packed array of anions, where A-site cations fill 1/8 of the tetrahedral holes and B-site cations fill 1/2 of the octahedral holes. In contrast, inverse spinel structures have all A cations and half of the B cations occupying octahedral sites, and the other half of B cations occupying tetrahedral sites. The choice between the normal and inverse spinel structures is primarily driven by the crystal field stabilization energy (CFSE) of the cations.
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