CaO
calcium oxide · quicklime, burnt lime
Calcium oxide is a stable, insulating inorganic compound commonly known as quicklime that plays a vital role in industrial manufacturing and chemical processing.
About calcium oxide
Calcium oxide is a fundamental inorganic compound that exists as a thermodynamically stable solid. Its character as a wide-gap insulator makes it a critical component in various high-temperature industrial applications where chemical stability is paramount.
Due to its extensive history and utility, this material is exceptionally well-documented in structural databases. It serves as a cornerstone in materials chemistry, providing a reliable foundation for the synthesis of more complex ceramic and mineral systems.
Key Properties
Cross-validated computational properties for calcium oxide, aggregated across 4 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 CaO. 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 CaO, 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. |
|---|---|---|---|---|---|
| Fm-3m (No. 225) | cubic | 3.63 | 0.0000 | -6.783 | 3.35 |
| P63/mmc (No. 194) | hexagonal | 3.12 | 0.1043 | -6.678 | 2.82 |
| Cmce (No. 64) | orthorhombic | 2.09 | 0.2098 | -6.573 | 2.00 |
| I4/mmm (No. 139) | tetragonal | 1.74 | 0.2099 | -6.573 | 1.97 |
| P1 (No. 1) | triclinic | 2.47 | 0.2954 | -6.487 | 2.82 |
| P1 (No. 1) | triclinic | 2.14 | 0.3111 | -6.472 | 2.81 |
| P1 (No. 1) | triclinic | 2.00 | 0.3415 | -6.441 | 2.79 |
| Fd-3m (No. 227) | cubic | 0.00 | 2.7281 | -4.055 | 2.97 |
| No. 0 | unknown | — | — | — | 0.83 |
| No. 0 | unknown | — | — | — | 0.79 |
| No. 0 | unknown | — | — | — | 0.79 |
| No. 0 | unknown | — | — | — | 0.82 |
Applications
Where calcium oxide is used.
Frequently Asked Questions
Common questions about calcium oxide, answered from cross-validated data.
What is CaO?
Calcium oxide is a stable, insulating inorganic compound commonly known as quicklime that plays a vital role in industrial manufacturing and chemical processing.
What is CaO used for?
What is the band gap of CaO?
Is CaO a metal, semiconductor, or insulator?
Is CaO thermodynamically stable?
What is the crystal structure of CaO?
What is the density of CaO?
How many polymorphs of CaO are known?
What elements does CaO contain?
Where does the data for CaO come from?
How It Compares
As a highly stable and well-characterized oxide, this compound serves as a primary reference material for alkaline earth metal oxides. Its structural simplicity and thermodynamic robustness distinguish it as a foundational building block in inorganic chemistry, setting the standard for stability within its chemical group.
Data sources & attribution
- materials_project — Data from the Materials Project. Cite: Jain et al., APL Materials 1, 011002 (2013).
- cod — Data from the Crystallography Open Database. Cite: Grazulis et al., Nucleic Acids Res. 40, D420 (2012).
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