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Barium fluoride
Identifiers
CAS Number	7787-32-8 ;
3D model (JSmol)	Interactive image; Interactive image;
ChemSpider	56421 ;
ECHA InfoCard	100.029.189
PubChem CID	62670;
RTECS number	CQ9100000;
UNII	H96A02I53Y ;
CompTox Dashboard (EPA)	DTXSID4064848 ;
	InChI InChI=1S/Ba.2FH/h;2*1H/q+2;;/p-2 Key: OYLGJCQECKOTOL-UHFFFAOYSA-L ;
	SMILES F[Ba]F; [Ba+2].[F-].[F-];
Properties
Chemical formula	BaF2
Molar mass	175.324 g/mol
Appearance	white cubic crystals
Density	4.893 g/cm3
Melting point	1,368 °C (2,494 °F; 1,641 K)
Boiling point	2,260 °C (4,100 °F; 2,530 K)
Solubility in water	1.58 g/L (10 °C); 1.61 g/L (25 °C)
Solubility product (Ksp)	1.84·10−7
Solubility	soluble in methanol, ethanol
Magnetic susceptibility (χ)	−51·10−6 cm3/mol
Thermal conductivity	10.9 W/(m·K)
Refractive index (nD)	1.557 (200 nm); 1.4744 (589 nm); 1.4014 (10 μm);
Structure
Crystal structure	Fluorite (cubic), cF12
Space group	Fm3m, No. 225
Lattice constant	a = 0.62 nm
Formula units (Z)	4
Thermochemistry
Heat capacity (C)	71.2 J/(mol·K)
Std molar; entropy (S⦵298)	96.4 J/(mol·K)
Std enthalpy of; formation (ΔfH⦵298)	−1207.1 kJ/mol
Gibbs free energy (ΔfG⦵)	−1156.8 kJ/mol
Hazards
	Occupational safety and health (OHS/OSH):
Main hazards	Toxic
	GHS labelling:
Pictograms
Flash point	Non-flammable
	Lethal dose or concentration (LD, LC):
LD50 (median dose)	250 mg/kg, oral (rat)
Safety data sheet (SDS)	PubChem
Related compounds
Other anions	Barium chloride; Barium bromide; Barium iodide;
Other cations	Beryllium fluoride; Magnesium fluoride; Calcium fluoride; Strontium fluoride; Radium fluoride;
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Barium fluoride is an inorganic compound with the formula Ba F₂. It is a colorless solid that occurs in nature as the rare mineral frankdicksonite.^[9] Under standard conditions it adopts the fluorite structure and at high pressure the PbCl₂ structure.^[10] Like CaF₂, it is resilient to and insoluble in water.

Above ca. 500 °C, BaF₂ is corroded by moisture, but in dry environments it can be used up to 800 °C. Prolonged exposure to moisture degrades transmission in the vacuum UV range. It is less resistant to water than calcium fluoride, but it is the most resistant of all the optical fluorides to high-energy radiation, though its far ultraviolet transmittance is lower than that of the other fluorides. It is quite hard, very sensitive to thermal shock and fractures quite easily.

Optical properties

Barium fluoride is transparent from the ultraviolet to the infrared, from 150 to 200 nm to 11–11.5 μm. It is used in windows for infrared spectroscopy, in particular in the field of fuel oil analysis. Its transmittance at 200 nm is relatively low (0.60), but at 500 nm it goes up to 0.96–0.97 and stays at that level until 9 μm, then it starts falling off (0.85 for 10 μm and 0.42 for 12 μm). The refractive index is about 1.46 from 700 nm to 5 μm.^[11]

Barium fluoride is also a common, very fast (one of the fastest) scintillators for the detection of X-rays, gamma rays or other high energy particles. One of its applications is the detection of 511 keV gamma photons in positron emission tomography. It responds also to alpha and beta particles, but, unlike most scintillators, it does not emit ultraviolet light.^[12] It can be also used for detection of high-energy (10–150 MeV) neutrons, using pulse shape discrimination techniques to separate them from simultaneously occurring gamma photons.

Barium fluoride is used as a preopacifying agent and in enamel and glazing frits production. Its other use is in the production of welding agents (an additive to some fluxes, a component of coatings for welding rods and in welding powders). It is also used in metallurgy, as a molten bath for refining aluminium.

Gas phase structure

In the vapor phase the BaF₂ molecule is non-linear with an F-Ba-F angle of approximately 108°.^[13] Its nonlinearity violates VSEPR theory. Ab initio calculations indicate that contributions from d orbitals in the shell below the valence shell are responsible.^[14] Another proposal is that polarisation of the electron core of the barium atom creates an approximately tetrahedral distribution of charge that interacts with the Ba-F bonds.^[15]

References

^ ^a ^b ^c ^d ^e Haynes, p. 4.49
^ Haynes, p. 5.167
^ John Rumble (June 18, 2018). CRC Handbook of Chemistry and Physics (99th ed.). CRC Press. pp. 4–47. ISBN 978-1138561632.
^ Haynes, p. 4.126
^ Haynes, p. 12.222
^ Haynes, p. 10.248
^ Hohnke, D. K.; Kaiser, S. W. (1974). "Epitaxial PbSe and Pb_1−xS_xSe: Growth and electrical properties". Journal of Applied Physics. 45 (2): 892–897. Bibcode:1974JAP....45..892H. doi:10.1063/1.1663334.
^ Haynes, p. 5.5
^ Radtke A.S., Brown G.E. (1974). "Frankdicksonite, BaF₂, a New Mineral from Nevada" (PDF). American Mineralogist. 59: 885–888.
^ Wells, A.F. (1984). Structural inorganic chemistry −5th Edition. Oxford: Clarendon Press. ISBN 0-19-855370-6.
^ "Crystran Ltd. Optical Component Materials". Archived from the original on 11 June 2010. Retrieved 29 December 2009.
^ Laval, M; Moszyński, M.; Allemand, R.; Cormoreche, E.; Guinet, P.; Odru, R.; Vacher, J. (1983). "Barium fluoride – Inorganic scintillator for subnanosecond timing". Nuclear Instruments and Methods in Physics Research. 206 (1–2): 169–176. Bibcode:1983NIMPR.206..169L. doi:10.1016/0167-5087(83)91254-1.
^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
^ Seijo, Luis; Barandiarán, Zoila; Huzinaga, Sigeru (1991). "Ab initio model potential study of the equilibrium geometry of alkaline earth dihalides: MX2 (M=Mg, Ca, Sr, Ba; X=F, Cl, Br, I)" (PDF). The Journal of Chemical Physics. 94 (5): 3762. Bibcode:1991JChPh..94.3762S. doi:10.1063/1.459748. hdl:10486/7315.
^ Bytheway, Ian; Gillespie, Ronald J.; Tang, Ting-Hua; Bader, Richard F. W. (1995). "Core Distortions and Geometries of the Difluorides and Dihydrides of Ca, Sr, and Ba". Inorganic Chemistry. 34 (9): 2407. doi:10.1021/ic00113a023.