The indium chalcogenides include all compounds of indium with the chalcogen elements, oxygen, sulfur, selenium and tellurium. (Polonium is excluded as little is known about its compounds with indium). The best characterised compounds are the In(III) and In(II) chalcogenides e.g. the sulfides In2S3 and InS.
This group of compounds has attracted a lot of research attention because they include semiconductors, photovoltaics and phase-change materials. In many applications indium chalcogenides are used as the basis of ternary and quaternary compounds such as indium tin oxide, ITO and copper indium gallium selenide, CIGS.
Contents
- In2O In2Se
- In4S3 In4Se3 In4Te3
- In5S4
- InS InSe InTe
- In6S7 In6Se7
- In3Te4
- In7Te10
- In2S3 In2Se3 In2Te3
- In3Te5
- In2Te5
- References
Some compounds that were reported and have found their way into text books have not been substantiated by later researchers. The list of compounds below shows compounds that have been reported, and those compounds that have not had their structure determined, or whose existence has not been confirmed by the latest structural investigations, are in italics.
There are a lot of compounds, the reason for this being that indium can be present as
The compound In2Te5 is a polytelluride containing the Te32− unit.
None of the indium chalcogenides can be described simply as ionic in nature, they all involve a degree of covalent bonding. However, in spite of this it is useful to formulate the compounds in ionic terms to get an insight into how the structures are built up. Compounds almost invariably have multiple polymorphs, that is they can crystallise in slightly different forms depending on either the method of production, or the substrate upon which they are deposited. Many of the compounds are made up of layers, and it is the different ways that the layers are stacked that is a cause of polymorphism.
In2O, In2Se
In2O is well documented. It exists in the gaseous phase and there are numerous reports of small amounts detected in the solid phase but no definitive structure has been published. It is now believed that the compound described as In2Se was actually a sample of In4Se3.In4S3, In4Se3, In4Te3
In4S3 had been reported but has more recently been re-investigated and is now believed not to exist. Both In4Se3 and In4Te3 are similar black crystalline solids and have been formulated to contain a non linear In35+ unit that is isoelectronic with Hg32+. For example the selenide is formulated as In+ In35+ 3Se2−.In5S4
A reinvestigation showed that the original sample was actually SnIn4S4.InS, InSe, InTe
In6S7, In6Se7
These compounds are isostructural, and have been formulated with indium in 3 different oxidation states, +1, +2 and +3. They have been formulated as e.g. In+ In24+ 3In3+ 7S2−. The indium – indium bond length in the In2 units are 2.741 A (sulfide), 2.760 (selenide).In6S7 is an n-type semiconductor.