Strontium bromide

Strontium bromide is a chemical compound with a formula SrBr2. At room temperature it is a white, odourless, crystalline powder. Strontium bromide imparts a bright red colour in a flame test, showing the presence of strontium ions. It is used in flares and also has some pharmaceutical uses.

Preparation
SrBr2 can be prepared from strontium hydroxide and hydrobromic acid.
 * Sr(OH)2 + 2 HBr → SrBr2 + 2 H2O

Alternatively strontium carbonate can also be used as strontium source.
 * SrCO3 + 2 HBr → SrBr2 + H2O + CO2(g)

These reactions give hexahydrate of strontium bromide (SrBr2*6H2O), which decomposes to dihydrate (SrBr2*2H2O) at 89 °C. At 180 °C anhydrous SrBr2 is obtained.

Structure
At room temperature, strontium bromide adopts a crystal structure with a tetragonal unit cell and space group P4/n. This structure is referred to as α-SrBr2 and is isostructural with EuBr2 and USe2. The compound's structure was initially erroneously interpreted as being of the PbCl2 type, but this was later corrected.

Around 920 K (650 °C), α-SrBr2 undergoes a first-order solid-solid phase transition to a much less ordered phase, β-SrBr2, which adopts the cubic fluorite structure. The beta phase of strontium bromide has a much higher ionic conductivity of about 1 S/cm, comparable to that of molten SrBr2, due to extensive disorder in the bromide sublattice. Strontium bromide melts at 930 K (657 °C).