, , is a ternary compound. An example is
sodium phosphate, . The
sodium ion has a charge of 1+ and the
phosphate ion has a charge of 3–. Therefore, three sodium ions are needed to balance the charge of one phosphate ion. Another example of a ternary compound is
calcium carbonate, . In naming and writing the formulae for ternary compounds, rules are similar to binary compounds.
Classifications of ternary crystals According to
Rustum Roy and Olaf Müller, "the chemistry of the entire mineral world informs us that
chemical complexity can easily be accommodated within structural simplicity." The example of
zircon is cited, where various metal atoms are replaced in the same
crystal structure. "The structural entity ... remains ternary in character and is able to accommodate an enormous range of chemical elements." The great variety of ternary compounds is therefore reduced to relatively few structures: "By dealing with approximately ten ternary structural groupings we can cover the most important structures of science and technology specific to the non-metallics world. It is a remarkable instance of nature's
simplexity." Letting A and B represent
cations and X an anion, these ternary groupings are organized by
stoichiometric types , , and . A ternary compound of type may be in the class of
olivine, the
spinel group, or
phenakite. Examples include , β-, and . One of type may be of the class of
zircon,
scheelite,
barite or an ordered
silicon dioxide derivative. In the class of ternary compounds, there are the structures of
perovskite (structure),
calcium carbonate,
pyroxenes,
corundum and hexagonal types. Other ternary compounds are described as crystals of types , , , , and .
Ternary semiconductors A particular class of ternary compounds are the ternary
semiconductors, particularly within the
III-V semiconductor family. In this type of semiconductor, the ternary can be considered to be an alloy of the two binary endpoints. Varying the composition between the endpoints allows both the lattice constant and the energy
bandgap to be adjusted to produce the properties desired, for example, in emitting light (for example, as a
LED) or absorbing light (as a
photodetector or a
photovoltaic cell). An example would be the semiconductor
indium gallium arsenide ({{chem2|In_{
x}Ga_{1–
x}As}}), a material with
band gap dependent on In/Ga ratio. Important examples of ternary semiconductors can also be found in other semiconductor families, such as the
II-VI family (
e.g.,
Mercury cadmium telluride, {{chem2|Hg_{1−
x}Cd_{
x}Te}}), or the I-II-VI2 family, with examples such as . ==Organics==