The key difference between spinel and inverse spinel structure is that in spinel structure, B ions occupy half the octahedral holes while A ions occupy 1/8th of the tetrahedral holes whereas, in inverse spinel structure, all A cations and half of the B cations occupy octahedral sites and the other half of B cations occupy tetrahedral sites.
The term spinel refers to any of a class of minerals having the general chemical formula AB2X4. These minerals tend to crystallize in the cubic crystal system. Spinels are often referred to as rubies, but a ruby is not a spinel.
CONTENTS
1. Overview and Key Difference
2. What is a Spinel Structure
3. What is an Inverse Spinel Structure
4. Side by Side Comparison – Spinel vs Inverse Spinel Structure in Tabular Form
5. Summary
What is Spinel Structure?
A spinel is any class of minerals having the general chemical formula AB2X4. These structures are often cubic crystal systems. In the above general formula, “X” is an anion (typically, this anion is a chalcogen such as oxygen and sulfur) and the ions are arranged in a cubic close-packed lattice. “A” and “B” are cations that tend to occupy some or all of the octahedral and tetrahedral sites in the lattice. According to the general formula, the charges on the A and B cations are +2 and +3, respectively. However, divalent, trivalent and tetravalent cations are also possible in this combination. Normally, the X anion is oxygen. If the anion is some other chalcogen, the structure is named as thiospinel structure.
In this structure, A and B cations can be the same metal having two different valences. For example, magnetite is a mineral having the chemical formula Fe3O4, and it contains both ferrous and ferric ions. Usually, we can classify spinel structures according to the B cation.
For example, aluminum spinel group, iron spinel group, chromium spinel group, cobalt spinel group, etc. The space group for a spinel structure is same as the structure of diamond except for some cases. Normally, these structures have a cubic close-packed oxide structure with eight tetrahedral and four octahedral sites per formula unit. Here, the tetrahedral spaces are smaller than the octahedral spaces. Also, B ions occupy half the octahedral holes while A ions occupy 1/8th of the tetrahedral holes.
What is Inverse Spinel Structure?
Inverse spinel structure is a derivative of the normal spinel structure of mineral lattices. It is also applied for the minerals having the general formula AB2X4. Unlike the normal spinel structure, the inverse spinel structure has all the A cations and half of the B cations occupying octahedral sites while the other half of B cations occupy tetrahedral sites. A common example of the inverse spinel structure is Fe3O4. Here, ferrous ions are the A cations, and ferric ions are the B cations.
What is the Difference Between Spinel and Inverse Spinel Structure?
Spinel and inverse spinel are two mineral structures having crystal lattice systems. The key difference between spinel and inverse spinel structure is that in spinel structure, B ions occupy half the octahedral holes while A ions occupy 1/8th of the tetrahedral holes whereas, in inverse spinel structure, all A cations and half of the B cations occupy octahedral sites and the other half of B cations occupy tetrahedral sites.
Below infographic summarizes the difference between spinel and inverse spinel structure.
Summary – Spinel vs Inverse Spinel Structure
Spinel and inverse spinel are two mineral structures having crystal lattice systems. The key difference between spinel and inverse spinel structure is that in spinel structure, B ions occupy half the octahedral holes while A ions occupy 1/8th of the tetrahedral holes whereas, in inverse spinel structure, all A cations and half of the B cations occupy octahedral sites and the other half of B cations occupy tetrahedral sites.
Reference:
1. Spinel group. (2020, July 19). Retrieved July 28, 2020, from Available here
Image Courtesy:
1. “Spinel” By Materialscientist at English Wikipedia (CC BY-SA 3.0) via Commons Wikimedia