Al2Si2O7
metakaolin · calcined kaolin
Al2Si2O7 is a reactive, insulating aluminosilicate phase typically produced by the heat treatment of kaolinite clay.
About metakaolin
Al2Si2O7 is an insulating aluminosilicate framework that represents a critical intermediate phase in the thermal transformation of clay minerals. Its structure is characterized by a disordered arrangement of aluminum and silicon polyhedra, which arises during the dehydration process of its parent mineral.
This compound is highly significant in materials science due to its metastable nature and high chemical reactivity. Its ability to participate in geopolymerization and cementitious reactions makes it a foundational component in the development of sustainable construction materials and specialized ceramics.
Key Properties
Cross-validated computational properties for metakaolin, 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 Al2Si2O7. 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 Al2Si2O7, 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. |
|---|---|---|---|---|---|
| C2/c (No. 15) | monoclinic | 5.44 | 0.0053 | -3.092 | — |
| C2/c (No. 15) | monoclinic | 5.05 | 0.0230 | -8.142 | 3.20 |
| — | — | 5.63 | 0.0864 | -3.082 | — |
| P1 (No. 1) | triclinic | 3.70 | 0.2809 | -7.884 | 2.11 |
| C2/c (No. 15) | monoclinic | — | — | — | 3.10 |
| C2/c (No. 15) | monoclinic | — | — | — | 3.30 |
| C2/c (No. 15) | monoclinic | — | — | — | 3.18 |
Synthesis Routes
Literature-extracted synthesis procedures targeting Al2Si2O7.
Applications
Where metakaolin is used.
Frequently Asked Questions
Common questions about metakaolin, answered from cross-validated data.
What is Al2Si2O7?
Al2Si2O7 is a reactive, insulating aluminosilicate phase typically produced by the heat treatment of kaolinite clay.
What is Al2Si2O7 used for?
What is the band gap of Al2Si2O7?
Is Al2Si2O7 a metal, semiconductor, or insulator?
Is Al2Si2O7 thermodynamically stable?
What is the crystal structure of Al2Si2O7?
How many polymorphs of Al2Si2O7 are known?
How is Al2Si2O7 synthesized?
What elements does Al2Si2O7 contain?
Where does the data for Al2Si2O7 come from?
How It Compares
Within the aluminosilicates and zeolite frameworks class.
Within the diverse family of aluminosilicates, Al2Si2O7 is distinguished by its unique role as a reactive, metastable phase compared to the more thermodynamically stable, naturally occurring minerals like Al2SiO5 or the framework-structured NaAlSi3O8. While many members of this class, such as LiAlSiO4 or KAlSiO4, are defined by their rigid crystalline zeolite frameworks, Al2Si2O7 is prized specifically for its structural disorder and potential for further chemical activation.
Related Compounds
Other Aluminosilicates and Zeolite Frameworks in the database.
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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