Doping Influence on the Defect Structure and Ionic Conductivity of Fluorine-containing Phases - Functionalized Inorganic Fluorides - page 459

Because all anion positions of both Bi 1 x Ba x (O , F) 3 modifications [34] are occupied
by mobile F ions (contrary to the stoichiometric oxyfluoride ThOF 2 ), inflections in
temperature dependences of the conductivity at 400-430 K appear (Figure 14.36). The
reason for this phenomenon consists in the involvement of anion positions of the F2,3
sublattice in transport processes. Both regions of this dependence are well described in
terms of the Arrhenius-Frenkel equation: T ¼ 0 exp[E a /kT]. At low temperatures, E a1
0.56-0.63 eV and above T c , the ions of both sublattices are mobile and the conductivity
activation energy falls down to E a2 0.12-0.16 eV.

1

Bi 0,96 Ba 0,04 O y F 2,96-2y

lg σ T
S CM -1 K

0

y = 0,15

-1

y = 0,0375

y = 0,0675

-2

y = 0,0875

-3

2,0 2,4 2,8 3,2 3,6

1000/T,K

Figure 14.36 Temperature dependencies of conductivity of Bi 0,96 Ba 0,4 O y F 2,962y samples [34]

The conductivity of tysonites, as well as that of fluorites, is affected by the presence of
polarizable cations with a lone electron pair. The temperature dependences of conductivity
of modifications I and II, for Bi 1 x Nd x (O,F) 3 solid solutions (Figure 14.28) are pre-
sented in Figure 14.37[22]. The conductivity of solid solutions under investigation
increases, in both phases, when the bismuth ions content (and correspondingly, deficit of
anions) increases. But the conductivity is higher by one or two orders of magnitude in
modification I which contains more anion vacancies.

14.8.3 Concentration Dependences of Ionic Conductivity in Tysonite-like Solid
Solutions

Similarly to fluorite-like solid solutions, maxima on the concentration dependence curve
of conductivity were found for heterovalent doping tysonite-like solid solutions with I and
II structures (Figure 14.38 [115] and 14.39 [34]).