  Broadband dielectric spectroscopy from Hz up to the infrared (IR) range and
temperature interval 10-300 K was carried out for xBaZrO3-(1-x)BaTiO3 (BZT-x, x
= 0.6, 0.7, 0.8) solid solution ceramics and compared with similar studies for
x = 0, 0.2, 0.4, 1 ceramics published recently (Phys. Rev. B 86, 014106
(2012)). Rather complex IR spectra without appreciable mode softening are
ascribed to Last-Slater transverse optic (TO) phonon eigenvector mixing and
possible two-mode mixed crystal behavior. Fitting of the complete spectral
range requires a relaxation in the 100 GHz range for all the samples. Below 1
GHz another relaxation appears, which is thermally activated and obeys the same
Arrhenius behavior for all the relaxor BZT samples. The frequently reported
Vogel-Fulcher behavior in BZT relaxors is shown to be an artifact of the
evaluation from the permittivity or loss vs. temperature dependences instead of
its evaluation from loss vs. frequency maxima. The relaxation is assigned to
local hopping of the off-centered Ti4+ ions in the frozen BTO clusters, whose
size is rather small and cannot grow on cooling. Therefore BZT is to be
considered as a dipolar glass rather than relaxor ferroelectric.
