ZnO
Zinc oxide · zinc white, Chinese white, philosopher's wool, flowers of zinc
ZnO is zinc oxide, a thermodynamically stable binary compound of zinc and oxygen. It usually crystallizes in the hexagonal wurtzite structure and is a wide-band-gap semiconductor that is normally n-type as grown. It is widely used as a rubber vulcanization activator, as a component of copper-based methanol synthesis catalysts, in varistors, and as an ultraviolet filter.
About Zinc oxide
What is ZnO and what structure does it adopt?
ZnO is a binary oxide of zinc and oxygen. At ambient conditions it adopts the hexagonal wurtzite structure, in which every zinc and oxygen atom is tetrahedrally coordinated. A metastable cubic zinc-blende form can be grown under certain conditions, such as on cubic substrates, and at high pressure ZnO changes to a rocksalt structure.
What is ZnO used for?
Zinc oxide is used in chemical manufacturing, electronics, and personal care. It is an essential activator in rubber vulcanization. In heterogeneous catalysis it is a key component of the copper/zinc oxide/alumina catalysts used for industrial methanol synthesis, and it is studied for carbon dioxide hydrogenation. In devices, its wide direct band gap, piezoelectricity, and the nonlinear electrical behaviour of its ceramics make it useful for varistors, gas sensors, transparent conducting layers (when doped, for example with aluminium), and acoustic-wave devices. Its strong ultraviolet absorption and low skin toxicity have made it a widely used mineral sunscreen filter, and it is also used as a white pigment (zinc white).
How stable and synthesizable is ZnO?
ZnO is a thermodynamically stable compound at ambient conditions and has been made and used on a large scale for a long time. Industrial routes include the indirect (French) process, in which zinc metal is vaporized and oxidized, and the direct (American) process, in which zinc ore is reduced and the resulting zinc vapour is oxidized. In the laboratory it is made by thermal decomposition or calcination of zinc salts and hydroxides, hydrothermal growth, and sol-gel deposition. These methods give bulk ceramics, single crystals, thin films, and many kinds of nanostructures.
Is ZnO a semiconductor and what does that imply?
Yes. ZnO is a wide-band-gap semiconductor that is normally n-type as grown. The origin of this unintentional n-type conductivity is still debated. Oxygen vacancies and zinc interstitials were long blamed, but first-principles studies suggest oxygen vacancies are deep donors, so hydrogen and other impurities such as aluminium or gallium are also strong candidates. Reliable p-type doping is still difficult to achieve. Gases adsorbing on the surface change its conductivity, which is the basis for ZnO gas sensors. In varistors, electrical barriers at the grain boundaries of doped ZnO ceramics give the strongly nonlinear current-voltage response used for surge protection.
How does ZnO compare to CuO, NiO, and other oxides?
In CuO and NiO the metal d shells are only partly filled, which gives these oxides magnetic ordering and colour. Zinc in ZnO is Zn2+ with a completely filled 3d shell, so ZnO is diamagnetic and white, with a wide direct band gap. Wide-gap oxides such as the spinel MgAl2O4 or the perovskite LaAlO3 are electrical insulators. ZnO is unusual because it combines transparency to visible light with electrical conduction that can be tuned by doping.
Key Properties
Cross-validated computational properties for Zinc oxide, aggregated across 3 databases.
Band GapEnergy needed to move an electron from the valence band to the conduction band. Lower or zero values tend to behave more metallic; larger gaps are more insulating or semiconducting.
Energy Above HullThermodynamic distance from the most stable set of competing phases. 0 eV/atom is on the convex hull; small positive values may still be experimentally accessible.
StabilityA plain-language summary of the best reported energy-above-hull result. It reflects whether the lowest-energy structure is on, near, or far from the stability hull.
StructuresCount of reported calculated crystal structures for this formula, including alternate polymorphs, source databases, and observed space groups.
Cross-Source DFT Agreement
How well independent DFT databases agree on the thermodynamics of ZnO. Tight agreement means computed properties can be trusted without re-running calculations.
Agreement ScoreA normalized confidence score summarizing how closely independent DFT databases agree. Higher scores mean tighter cross-source agreement.
Hull SpreadDifference between the highest and lowest energy-above-hull values reported by comparable sources. Smaller spread means less thermodynamic disagreement.
Sources ComparedNumber and names of computational sources with comparable entries for this formula.
Space Group ConsensusWhether independent sources predict the same crystal symmetry for the lowest-energy structure.
Reported Structures
Lowest-energy structures reported for ZnO, ranked by energy above hull.
| Space GroupSymmetry classification of the crystal arrangement. The number is the international space-group index. | Crystal SystemBroad lattice family, such as cubic, tetragonal, monoclinic, or triclinic, derived from unit-cell symmetry. | Band Gap (eV)Electronic gap calculated for this specific reported structure, measured in electronvolts. | E above hull (eV/atom)Thermodynamic distance from the convex hull for this structure, normalized per atom. Lower is generally more stable. | E/atom (eV)Computed total energy normalized per atom. Use energy above hull, not this value alone, when comparing stability. | Density (g/cm³)Mass per relaxed crystal volume, reported in grams per cubic centimeter. |
|---|---|---|---|---|---|
| — | — | 1.04 | 0.0000 | -1.649 | — |
| P63mc (No. 186) | hexagonal | 0.96 | 0.0000 | -1.592 | — |
| P63mc (No. 186) | hexagonal | 0.73 | 0.0000 | -4.895 | 5.70 |
| F-43m (No. 216) | cubic | 0.87 | 0.0060 | -1.586 | — |
| — | — | 0.97 | 0.0069 | -1.642 | — |
| F-43m (No. 216) | cubic | 0.63 | 0.0081 | -4.887 | 5.71 |
| — | — | 1.06 | 0.0253 | -1.624 | — |
| P42/mnm (No. 136) | tetragonal | 0.74 | 0.0329 | -4.862 | 5.45 |
| — | — | 1.25 | 0.0635 | -1.585 | — |
| — | — | 1.14 | 0.0759 | -1.573 | — |
| Fm-3m (No. 225) | cubic | 1.08 | 0.1272 | -1.465 | — |
| — | — | 1.08 | 0.1432 | -1.506 | — |
Synthesis Routes
Literature-extracted synthesis procedures targeting ZnO.
Applications
Where Zinc oxide is used.
Patent Landscape
70 patents reference ZnO or close compositional variants.
| Patent | Title | Assignee | Granted |
|---|---|---|---|
| 8790614 | ZnO structures and methods of use | — | — |
| 4873118 | Oxygen glow treating of ZnO electrode for thin film silicon solar cell | — | — |
| 8137458 | Epitaxial growth of ZnO with controlled atmosphere | — | — |
| 7115213 | Ferromagnetic ZnO-type compound including transition metallic element and method for adjusting ferromagnetic c | — | — |
| 4111852 | Pre-glassing method of producing homogeneous sintered ZnO non-linear resistors | — | — |
| 6808743 | Growth of ZnO film using single source CVD | — | — |
| 8992883 | Polymer-mediated synthesis of ZnO nanostructures | — | — |
| 7033435 | Process for preparing p-n junctions having a p-type ZnO film | — | — |
| 8395152 | Stable P-type semiconducting behaviour in Li and Ni codoped ZnO | — | — |
| 9950315 | Ni—MgO—ZnO solid catalysts for syngas preparation and process for the preparation thereof | — | — |
Frequently Asked Questions
Common questions about Zinc oxide, answered from cross-validated data and the published literature.
Is ZnO the same as calamine?
Not exactly. Calamine lotion is mainly zinc oxide with a small amount of iron(III) oxide (ferric oxide), which gives its pink colour. The name calamine has also been used for zinc ore minerals.
What crystal structure does ZnO normally have?
Is zinc oxide safe in sunscreen?
Why is ZnO used with copper in methanol synthesis catalysts?
Does ZnO conduct electricity?
What is ZnO?
What is ZnO used for?
What is the band gap of ZnO?
Is ZnO a metal, semiconductor, or insulator?
Is ZnO thermodynamically stable?
What is the crystal structure of ZnO?
How many polymorphs of ZnO are known?
How is ZnO synthesized?
What elements does ZnO contain?
Where does the data for ZnO come from?
Related Research
A band gap sets whether a solid is a metal, semiconductor or insulator. Learn direct vs indirect gaps, how gaps are measured, and why DFT underestimates them.
What makes a transparent conducting oxide work, why indium tin oxide dominates, and how FTO, AZO, silver nanowires, and graphene compare as ITO alternatives.
Related Compounds
Other Wide-Bandgap Oxide Semiconductors in the database.
Data sources & attribution
- oqmd — Data from the OQMD (oqmd.org). Cite: Saal et al., JOM 65, 1501 (2013); Kirklin et al., npj Comp. Mater. 1, 15010 (2015). (CC-BY-4.0)
- jarvis — Data from JARVIS (jarvis.nist.gov), NIST. Cite: Choudhary et al., npj Comp. Mater. 6, 173 (2020). (LicenseRef-US-Gov-PD)
- materials_project — Data from the Materials Project (materialsproject.org). Cite: Jain et al., APL Materials 1, 011002 (2013). (CC-BY-4.0)
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