Article: Zinc oxide

Zinc oxide
General
Other names	Zinc white, calamine
Molecular formula	ZnO
Molar mass	81.41 g/mol
Appearance	White solid
Crystal Structure	cubic
CAS number	[1314-13-2][1]
Properties
Density and phase	5.606 g/cm3, solid
Solubility in water	Insoluble
Melting point	1975°C (decomposes)
Boiling point
Mohs hardness	5
a Lattice constant	4.63Å
Thermodynamic data
Standard enthalpy of formation ΔfH°solid	−348.0 kJ/mol
Standard molar entropy S°solid	43.9 J.K−1.mol−1
Hazards
EU classification	Dangerous for the environment (N)
R-phrases	R20, R36, R37.
S-phrases	S60, S61.
NFPA 704
Supplementary data page
Structure and properties	n, εr, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Regulatory data	Flash point, RTECS number, etc.
Related compounds
Other anions	Zinc sulfide Zinc selenide Zinc telluride
Other cations	Cadmium oxide Mercury oxide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Zinc oxide is a chemical compound with formula ZnO. It is nearly insoluble in water but soluble in acids or alkalis. It occurs as white hexagonal crystals or a white powder commonly known as zinc white. It remains white when exposed to hydrogen sulfide or ultraviolet light. Crystalline zinc oxide exhibits the piezoelectric effect, is luminescent (it will change colour from white to yellow when heated, and back again when cooled down), and is light sensitive. Zinc oxide decomposes into zinc vapor and oxygen at around 1975°C.

Zinc oxide occurs in nature as the mineral zincite.

Applications

Zinc peroxide, ZnO₂ .½ H₂O, is a white to yellow powder used in antiseptic ointments, like Calamine Lotion.

Zinc white is used as a pigment in paints and is less opaque than lithopone, but more transparent than titanium dioxide. It is also used in coatings for paper. Chinese white is a special grade of zinc white used in artists' pigments. Because it absorbs both UVA and UVB rays of ultraviolet light, zinc oxide can be used in ointments, creams, and lotions to protect against sunburn and other damage to the skin caused by ultraviolet light.

Zinc oxide and stearic acid are important ingredients in the commercial manufacture of rubber goods. A proper mixture of these two compounds allows a quicker and more controllable rubber cure. Zinc oxide can also be used as a filler in some rubber mixtures.

Zinc oxide is a semiconductor with a direct band gap of 3.2 eV (387 nm, deep violet/borderline UV). A common application is in gas sensors. As of 2003, it has been utilized in recent research to build blue LEDs and transparent TFTs.

N-type doped films are often used in thin film technology, where zinc oxide serves as a TCO (transparent conducting oxide). N-type doping is possible by introduction of hydrogen or zinc interstitial defects. oxygen vacancies are no longer considered to contribute to the n-type conductivity because these levels are too deep in the band gap. P-type doping is difficult and is currently an active area of research. Thin-film solar cells, LCD and flat panel displays are typical applications of this material. Zinc oxide is transparent and conductive, and can therefore be used as a transparent electrode. Indium tin oxide (ITO) is another transparent conducting oxide often used in microelectronics.

ZnO has also been considered for spintronics applications because of theoretical predictions of room temperature ferromagnetism. Unsubstantiated reports of ferromagnetism have been reported, but presence of dilute magnetic semiconductors remains a large unanswered question in physics.

ZnO layers are mainly deposited by sputtering and chemical vapor deposition (CVD). The latter method allows the growth of a rough layer, which can diffuse the incoming light by scattering, increasing the efficiency of solar cells.

Pyroelectric coefficient

• Primary pyroelectric coefficient: -6.8 μC/m²·K
• Secondary pyroelectric coefficient: -2.5 μC/m²·K
• Total pyroelectric coefficient: -9.4 μC/m²·K