Complex ions in ammonium hexafluorohafnate:crystal structure and internal dynamics

摘要

The crystal structure of (NH_4)_2HfF_6 was determined using a SMART 1000 CCD diffractometer (MoK-(alpha) radiation,graphite monochromator).The unit cell parameters are a=13.3902(7) A,b=7.6850(4) A,c=11.6731(6)A,spacegroup Pca2_1,and Z=8;least-square refinement in the anisotropic approximation gave R_1=0.0299 and wR_2=0.0682.The compound is isostructural to (NH_4)_2XrF_6.The dynamics of the complex ions was examined in the temperature range 200-425K;the energy of their activation was estimated.It was found that compounds of the (NH_4)_2AF_6 type (A=Zr or Hf) can be classified as superionic conductors at 380 to 428K.