Strontium fluoride, SrF₂, also called strontium difluoride and strontium(II) fluoride, is a

fluoride Fluoride (). According to this source, is a possible pronunciation in British English. is an inorganic, monatomic anion of fluorine, with the chemical formula (also written ), whose salts are typically white or colorless. Fluoride salts typ ...

strontium Strontium is the chemical element with the symbol Sr and atomic number 38. An alkaline earth metal, strontium is a soft silver-white yellowish metallic element that is highly chemically reactive. The metal forms a dark oxide layer when it is ex ...

. It is a brittle white crystalline solid. In nature, it appears as the very rare mineral strontiofluorite.

Preparation

Strontium fluoride is prepared by the action of

hydrofluoric acid Hydrofluoric acid is a Solution (chemistry), solution of hydrogen fluoride (HF) in water. Solutions of HF are colourless, acidic and highly Corrosive substance, corrosive. It is used to make most fluorine-containing compounds; examples include th ...

on strontium carbonate.

Structure

The solid adopts the fluorite structure. In the vapour phase the SrF₂ molecule is non-linear with an F−Sr−F angle of approximately 120°. This is an exception to VSEPR theory which would predict a linear structure. Ab initio calculations have been cited to propose that contributions from d orbitals in the shell below the valence shell are responsible. Another proposal is that polarization of the electron core of the strontium atom creates an approximately tetrahedral distribution of charge that interacts with the Sr−F bonds.Core Distortions and Geometries of the Difluorides and Dihydrides of Ca, Sr, and Ba Bytheway I, Gillespie RJ, Tang TH, Bader RF Inorganic Chemistry, Vol.34, No.9, 2407-2414, 1995

Properties

It is almost insoluble in water (its K_sp value is approximately 2.0x10⁻¹⁰ at 25

degrees Celsius The degree Celsius is the unit of temperature on the Celsius scale (originally known as the centigrade scale outside Sweden), one of two temperature scales used in the International System of Units (SI), the other being the Kelvin scale. The ...

). It irritates eyes and skin, and is harmful when inhaled or ingested.
Similar to CaF₂ and BaF₂, SrF₂ displays

superionic conductivity Superionic water, also called superionic ice or ice XVIII is a phase of water that exists at extremely high temperatures and pressures. In superionic water, water molecules break apart and the oxygen ions crystallize into an evenly spaced latti ...

at elevated temperatures.https://web.archive.org/web/20051214052733/http://www.newmet.co.uk/Products/koch/strontium.php
/ref> Strontium fluoride is transparent to light in the wavelengths from vacuum ultraviolet (150 nm) to

infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

(11

µm The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Unit ...

). Its optical properties are intermediate to calcium fluoride and barium fluoride.

Uses

Strontium fluoride is used as an

optical material Optical materials are transparent materials from which optical lenses, prisms, windows, waveguides, and second-surface mirrors can be made. They are required in most optical instruments. Most optical materials are rigid solids, but flexible and ...

for a small range of special applications, for example, as an

optical coating An optical coating is one or more thin layers of material deposited on an optical component such as a lens, prism or mirror, which alters the way in which the optic reflects and transmits light. These coatings have become a key technology in th ...

on lenses and also as a thermoluminescent

dosimeter A radiation dosimeter is a device that measures dose uptake of external ionizing radiation. It is worn by the person being monitored when used as a personal dosimeter, and is a record of the radiation dose received. Modern electronic personal dos ...

crystal. Another use is as a carrier of strontium-90 radioisotope in

radioisotope thermoelectric generator A radioisotope thermoelectric generator (RTG, RITEG), sometimes referred to as a radioisotope power system (RPS), is a type of nuclear battery that uses an array of thermocouples to convert the heat released by the decay of a suitable radioacti ...

References

{{Authority control Fluorides Strontium compounds Optical materials Crystals Alkaline earth metal halides Fluorite crystal structure