HfB2: enthalpy of formation

7 accepted literature formation-enthalpy value(s) (experimental 6, model 1); experimental median -105.8 kJ/mol-atom (n = 6); Materials Project -98.211 kJ/mol-atom (mp-aaaaacys); OQMD -98.749 kJ/mol-atom (oqmd-5848).

Systems: B–Hf

Literature values

Enthalpy of formation of HfB2 reported in the literature (7)
Value	Phase as printed	T (K)	Class	Method	System	Source	Location
-117.633 kJ/mol-atom	HfB2	298.15	experimental	Langmuir vaporization	B–Hf	[1] Bittermann 1997 cites Krupka 1962	Table 3, p. 4, row 13 report
-109.633 kJ/mol-atom ± 2.93333	HfB2	298.15	experimental	Fluorine bomb calorimetry	B–Hf	[1] Bittermann 1997 cites ref. 67Joh	Table 3, p. 4, row 15 report
-106.567 kJ/mol-atom	HfB2	298.15	experimental	Langmuir vaporization	B–Hf	[1] Bittermann 1997 cites ref. 64	Table 3, p. 4, row 14 report
-105.033 kJ/mol-atom	HfB2	298.15	experimental	Tensimetric (reduction of HfO2 to HfB2 with B and B4C)	B–Hf	[1] Bittermann 1997 cites Paderno 1959	Table 3, p. 4, row 12 report
-87.3 kJ/mol-atom ± 1.66667	HfB2	298.15	experimental	Self-sustaining high-temperature synthesis calorimetry	B–Hf	[1] Bittermann 1997 cites Maslov 1978	Table 3, p. 4, row 17 report
-83.1333 kJ/mol-atom ± 1.96667	HfB2	298.15	experimental	Self-sustaining high-temperature synthesis calorimetry	B–Hf	[1] Bittermann 1997 cites Kitpichev 1979	Table 3, p. 4, row 18 report
-106.567 kJ/mol-atom	HfB2		model		B–Hf	[1] Bittermann 1997	Table 3, p. 4, row 20 report

Uncertainty budget

Components kept separate, in the value's unit (literature SCHEMA.md, UNCERTAINTY_CALIBRATION.md): effective = max(sqrt(max(printed, reading, method)^2 + composition^2 + conversion^2), scatter). The method floor is the robust between-study scatter of the method class in ORCHID (calibrated) or a documented prior; printed values and printed uncertainties are unchanged.

Uncertainty budget of the literature values of HfB2
Value	Unit	Printed	Reading	Method (class, basis)	Effective
-117.633	kJ/mol-atom		0.01667	4.2 (kems_vapour, calibrated)	4.2
-109.633	kJ/mol-atom	2.933	0.01667	1 (combustion_calorimetry, cleaned_below_threshold)	2.933
-106.567	kJ/mol-atom		0.01667	4.2 (kems_vapour, calibrated)	4.2
-105.033	kJ/mol-atom		0.01667	4.1 (experimental_unspecified, cleaned_below_threshold)	4.1
-87.3	kJ/mol-atom	1.667	0.01667	3.2 (solution_reaction_calorimetry, calibrated)	3.2
-83.1333	kJ/mol-atom	1.967	0.01667	3.2 (solution_reaction_calorimetry, calibrated)	3.2
-106.567	kJ/mol-atom		0.01667	3.9 (model_calculated, calibrated)	3.9

DFT formation energies

Lowest-energy entries at this composition. Materials Project and OQMD use different energy references and are never averaged. 1 eV/atom = 96.485 kJ/mol-atom.

DFT formation energy of HfB2
Source	Entry	kJ/mol-atom	eV/atom	Space group	E above hull (kJ/mol-atom)	E above hull (eV/atom)	Theoretical
Materials Project	mp-aaaaacys	-98.211	-1.01789	P6/mmm	0	0	no
OQMD	oqmd-5848	-98.749	-1.02347	P6/mmm	0	0	no

DFT sources: A. Jain et al., Commentary: The Materials Project: A materials genome approach to accelerating materials innovation, APL Materials 1 (2013) 011002. doi:10.1063/1.4812323 (CC BY 4.0); J. E. Saal et al., JOM 65 (2013) 1501-1509; S. Kirklin et al., npj Comput. Mater. 1 (2015) 15010. doi:10.1007/s11837-013-0755-4 (CC BY 4.0);

Sources

H. Bittermann, P. Rogl, Critical assessment and thermodynamic calculation of the ternary system boron-hafnium-titanium (B-Hf-Ti), JPE 18, 24-47 (1997). doi:10.1007/bf02646757

Please cite

R. Arróyave, J. Saal, D. Shin, ORCHID-Values: thermodynamic and phase-equilibrium values read from the literature (version 2026.10; Version 1, machine-extracted), Zenodo (2026). doi:10.5281/zenodo.23735569
R. Arróyave, J. Saal, D. Shin, ORCHID-Parity: DFT-vs-experiment formation-enthalpy benchmark (version 2026.10; Version 1, machine-extracted), Zenodo (2026). doi:10.5281/zenodo.23735943
R. Arróyave, J. Saal, D. Shin, ORCHID data: umbrella record of the ORCHID datasets (version 2026.10; Version 1, machine-extracted), Zenodo (2026). doi:10.5281/zenodo.23736065

Also cite the original source of every value you use (paper_citation / paper_doi, and cited_dois for values the paper cites from earlier work); A. Jain et al., The Materials Project: A materials genome approach to accelerating materials innovation, APL Materials 1 (2013) 011002, https://doi.org/10.1063/1.4812323 (CC BY 4.0); J. E. Saal et al., JOM 65 (2013) 1501, https://doi.org/10.1007/s11837-013-0755-4 and S. Kirklin et al., npj Comput. Mater. 1 (2015) 15010, https://doi.org/10.1038/npjcompumats.2015.10 (CC BY 4.0); G. Kim, S. V. Meschel, P. Nash, W. Chen, Experimental formation enthalpies for intermetallic phases and other inorganic compounds, Scientific Data 4 (2017) 170162, https://doi.org/10.1038/sdata.2017.162; B. Hallstedt, The SGTE collection of binary datasets, Calphad 89 (2025) 102833, https://doi.org/10.1016/j.calphad.2025.102833 (CC BY 4.0), and the original assessment named in each file. Version 1, machine-extracted: values were read by language-model readers constrained to quote their source and checked automatically, and the release was then audited on the printed pages by adversarial audits, an independent second review of fit-facing records and a preliminary human review of a frozen sample. Flags such as accepted and ESPEI-ready record screening results, not certification; known issues are listed in the release notes.

@misc{orchid_literature_2026,
  author    = {Arr{\'o}yave, Raymundo and Saal, James and Shin, Dongwon},
  title     = {{ORCHID-Values: thermodynamic and phase-equilibrium values read from the literature}},
  version   = {2026.10},
  publisher = {Zenodo},
  year      = {2026},
  doi       = {10.5281/zenodo.23735569},
  url       = {https://doi.org/10.5281/zenodo.23735569},
  note      = {Version 1, machine-extracted}
}

@misc{orchid_dft_benchmark_2026,
  author    = {Arr{\'o}yave, Raymundo and Saal, James and Shin, Dongwon},
  title     = {{ORCHID-Parity: DFT-vs-experiment formation-enthalpy benchmark}},
  version   = {2026.10},
  publisher = {Zenodo},
  year      = {2026},
  doi       = {10.5281/zenodo.23735943},
  url       = {https://doi.org/10.5281/zenodo.23735943},
  note      = {Version 1, machine-extracted}
}

@misc{orchid_data_2026,
  author    = {Arr{\'o}yave, Raymundo and Saal, James and Shin, Dongwon},
  title     = {{ORCHID data: umbrella record of the ORCHID datasets}},
  version   = {2026.10},
  publisher = {Zenodo},
  year      = {2026},
  doi       = {10.5281/zenodo.23736065},
  url       = {https://doi.org/10.5281/zenodo.23736065},
  note      = {Version 1, machine-extracted}
}