Time-differential perturbed-angular-correlation study ofK2HfF6polymorphism

The thermal behavior of the hyperfine interaction in ${\mathrm{K}}_2$ ${\mathrm{HfF}}_6$ was investigated by means of the time-differential perturbed-angular-correlation technique between 293 and 750 K. The quadrupole parameters associated with the monoclinic, orthorhombic, cubic, and trigonal phases have been determined. An activation energy $E_a$=86±16 kJ/mol could be calculated for the monoclinic-to-orthorhombic phase transition taking place between 384 and 466 K. An analogy with the hyperfine interaction of the isomorphous compound ${\mathrm{K}}_2$ ${\mathrm{ZrF}}_6$ could be established.