CaI
CaI is a metallic, thermodynamically unstable calcium-iodine compound known for its high structural diversity in materials research.
About CaI
CaI is a calcium-iodine compound characterized by its metallic electronic nature. Unlike typical ionic halides, this specific stoichiometry exhibits a lack of a band gap, placing it in a unique category of metallic materials that challenge conventional bonding expectations. Its thermodynamic profile indicates it exists above the hull, suggesting it is a metastable or unstable phase under standard conditions. Despite this, it remains a subject of intense scientific curiosity due to the vast number of structural configurations reported for this chemical system across various databases. Researchers study these diverse structural arrangements to better understand the potential for exotic bonding states in alkaline earth metal halides.
Key Properties
Cross-validated computational properties for CaI, 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 CaI. 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 CaI, 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. |
|---|---|---|---|---|---|
| P4/nmm (No. 129) | tetragonal | 0.00 | 0.1225 | -1.169 | — |
| P63/mmc (No. 194) | hexagonal | 0.00 | 0.2027 | -1.089 | — |
| P-6m2 (No. 187) | hexagonal | 0.00 | 0.2304 | -2.955 | 4.07 |
| — | — | 0.00 | 0.2613 | -1.060 | — |
| — | — | 0.00 | 0.2661 | -1.055 | — |
| — | — | 0.00 | 0.2856 | -1.035 | — |
| — | — | 0.00 | 0.3492 | -0.972 | — |
| P4/mmm (No. 123) | tetragonal | 0.00 | 0.3738 | -0.918 | — |
| — | — | 0.00 | 0.3883 | -0.933 | — |
| — | — | 0.00 | 0.3886 | -0.932 | — |
| — | — | 0.00 | 0.3888 | -0.932 | — |
| — | — | 0.00 | 0.4493 | -0.872 | — |
Applications
Where CaI is used.
Frequently Asked Questions
Common questions about CaI, answered from cross-validated data.
What is CaI?
CaI is a metallic, thermodynamically unstable calcium-iodine compound known for its high structural diversity in materials research.
What is CaI used for?
What is the band gap of CaI?
Is CaI a metal, semiconductor, or insulator?
Is CaI thermodynamically stable?
What is the crystal structure of CaI?
What is the density of CaI?
How many polymorphs of CaI are known?
What elements does CaI contain?
Where does the data for CaI come from?
How It Compares
As a member of the calcium-iodine system, CaI represents a distinct structural challenge compared to more common, stable halide salts. While many binary halides favor simple ionic lattices, this phase demonstrates how metallic character can emerge in non-traditional stoichiometries, highlighting the complexity of the calcium-iodine phase space.
Data sources & attribution
- 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)
- 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)
- mpaloe — Data from MP-ALOE. Cite: Kuner et al., npj Comput. Mater. (2025), doi:10.1038/s41524-025-01834-9.
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