The indium chalcogenides include all compounds

Chemical compound

A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 of indium

Indium

Indium is a chemical element with the symbol In and atomic number 49. This rare, very soft, malleable and easily fusible post-transition metal is chemically similar to gallium and thallium, and shows the intermediate properties between these two...

 with the chalcogen

Chalcogen

The chalcogens are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family...

 elements, oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

, sulfur

Sulfur

Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...

, selenium

Selenium

Selenium is a chemical element with atomic number 34, chemical symbol Se, and an atomic mass of 78.96. It is a nonmetal, whose properties are intermediate between those of adjacent chalcogen elements sulfur and tellurium...

 and tellurium. (Polonium

Polonium

Polonium is a chemical element with the symbol Po and atomic number 84, discovered in 1898 by Marie Skłodowska-Curie and Pierre Curie. A rare and highly radioactive element, polonium is chemically similar to bismuth and tellurium, and it occurs in uranium ores. Polonium has been studied for...

 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

Indium(III) sulfide

Indium sulfide is the inorganic compound with the formula In2S3. Three different structures are known: yellow, α-In2S3 has a defect cubic structure, red β-In2S3 has a defect spinel, tetragonal, structure, and γ-In2S3 has a layered structure...

 and InS.

This group of compounds has attracted a lot of research attention because they include semiconductor

Semiconductor

A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...

s, photovoltaics

Photovoltaics

Photovoltaics is a method of generating electrical power by converting solar radiation into direct current electricity using semiconductors that exhibit the photovoltaic effect. Photovoltaic power generation employs solar panels composed of a number of solar cells containing a photovoltaic material...

 and phase-change materials. In many applications indium chalcogenides are used as the basis of ternary and quaternary compounds such as indium tin oxide

Indium tin oxide

Indium tin oxide is a solid solution of indium oxide and tin oxide , typically 90% In2O3, 10% SnO2 by weight. It is transparent and colorless in thin layers while in bulk form it is yellowish to grey...

, ITO and copper indium gallium selenide

Copper indium gallium selenide

Copper indium gallium selenide is a I-III-VI2 semiconductor material composed of copper, indium, gallium, and selenium. The material is a solid solution of copper indium selenide and copper gallium selenide...

, CIGS.


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.

oxide	sulfide	selenide	telluride
In2O		In2Se
	In4S3	In4Se3	In4Te3
	In5S4
	InS	InSe	InTe
	In6S7	In6Se7
	In3S4		In3Te4
			In7Te10
In2O3	In2S3	In2Se3	In2Te3
			In3Te5
			In2Te5

There are a lot of compounds, the reason for this being that indium can be present as

• In³⁺, oxidation state
  Oxidation state
  In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by...
  
   +3
• In⁺, oxidation state
  Oxidation state
  In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by...
  
   +1
• In₂⁴⁺ units, oxidation state
  Oxidation state
  In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by...
  
   of +2, also found in some indium halides
  Indium halides
  There are three sets of indium halides, the trihalides, the monohalides, and several intermediate halides.In the monohalides the oxidation state of indium is +1 and their proper names are indium fluoride, indium chloride, indium bromide and indium iodide.The intermediate halides contain indium with...
  
  , e.g. In₂Br₃.
• non linear In₃⁵⁺ units isoelectronic
  Isoelectronicity
  Two or more molecular entities are described as being isoelectronic with each other if they have the same number of electrons or a similar electron configuration and the same structure , regardless of the nature of the elements involved.The term valence isoelectronic is used when these molecular...
  
   with Hg₃²⁺.

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

InS, InSe

InS and InSe are similar, both contain In₂⁴⁺ and have a layer structure. InS for instance can be formulated In₂⁴⁺ 2S²⁻. InSe has two crystal forms β-InSe and γ-InSe that differ only in the way that the layers are stacked. InSe is a semiconductor

Semiconductor

A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...

 and a phase change material and has potential as an optical recording medium.

InTe

InTe in contrast to InS and InSe is a mixed valence indium compound containing In⁺ and In³⁺ and can be formulated as In⁺ In³⁺ 2Te²⁻. It is similar to TlSe and has tetrahedral InTe₄ units that share edges. It has potential for use in photovoltaic devices.

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.

In₃Te₄

This compound has been reported as a superconductor. An unusual structure has been proposed that is effectively In₄Te₄ but with one quarter of the indium positions vacant. There seems to be no short indium-indium distance that would indicate an In-In unit.

In₇Te₁₀

This is formulated as In₂⁴⁺ 12In³⁺ 20Te^2-. The In-In distance is 276.3pm. It has a similar structure to Ga₇Te₁₀ and Al₇Te₁₀

In₂S₃, In₂Se₃, In₂Te₃

In₂S₃

Indium(III) sulfide

Indium(III) sulfide

Indium sulfide is the inorganic compound with the formula In2S3. Three different structures are known: yellow, α-In2S3 has a defect cubic structure, red β-In2S3 has a defect spinel, tetragonal, structure, and γ-In2S3 has a layered structure...

 is a yellow or red high melting solid. It is an n-type semiconductor

N-type semiconductor

N-type semiconductors are a type of extrinsic semiconductor where the dopant atoms are capable of providing extra conduction electrons to the host material . This creates an excess of negative electron charge carriers....

.

In₂Se₃

Indium(III) selenide

Indium(III) selenide

Indium selenide is a compound of indium and selenium. It has potential for use in photovoltaic devices and it has been the subject of extensive research. The two most common forms α- and β- have defect wurtzite structures, however there are five known forms The α- β phase transition is...

 is a black compound with potential photo-optic applications.

In₂Te₃

Indium(III) telluride

Indium(III) telluride

Indium telluride is a chemical compound. It is an intermetallic compound, so it has properties intermediate from a metal alloy and a metal-nonmetal ionic crystal. As so, it has intermediate conductivity and is classified as a semiconductor....

 is a black high melting solid with applications as a semiconductor and in photo-optic applications. It has two crystalline forms, α- and β-.

In₃Te₅

This was reported in phase studies in 1964 but its structure has not been confirmed.

In₂Te₅

This is a polytelluride compound and the structure is made up of layers that in turn are made up of chains of linked InTe₄ tetrahedra where three of the Te atoms are bridging. There are Te atoms separate from the chains. The compound has been formulated as (2In³⁺ Te²⁻Te₃²⁻)_n counterbalanced with separate Te²⁻ ions. The structure is similar to Al₂Te₅.