Using the powder x-ray diffractometry method, we have obtained for the
first time data on the lattice parameters of CoCl2 in the temperature
range from 5 to 293 K. The room-temperature lattice parameters are in
good agreement with the previously known values of other researchers.
With the aid of the data obtained we estimate tile spontaneous magnet
ostriction in tile ordered phase of this chloride. The estimated latti
ce distortions at the phase transition coincide in sign with those in
NiCl2 but are opposite to those in FeCl2.