Doping Influence on the Defect Structure and Ionic Conductivity of Fluorine-containing Phases - Functionalized Inorganic Fluorides - page 444

Lu Yb Er Y Dy Td Gd Sm

lg σ 293 K (S/c m )

Al Ga Sb Sc In La

-4

-5

-6

0.6 0.8 1.0 1.2 r i , Å

Figure 14.19 Ionic conductivity dependence of Pb 0.9 R 0.1 F 2.1 phases, at 293 K, on the R 3þ
ionic radius. (Reprinted with permission from [10] Copyright (1997) Pleiades Publishing Inc.)

It is shown in [67] for Cd 0.9 R 0.1 F 2.1 (R ¼ La-Lu, Y) that ionic conductivity ( 500K )of
fluorites of various RE elements correlates with concentration of interstitial fluoride ions
(F i(48g) þ F i(32f)1 þ F i(32f)2 ) located on the periphery of clusters. These interstitial fluoride
ion concentrations were measured by means of single-crystal X-ray diffraction (XRD).
The concentration and mobility of charge carriers depend on the cluster type forming the
defect region. At a RF 3 concentration called the percolation limit - x per - defect regions
combine themselves in joint conductivity channels. It results in a sharp conductivity
increase in fluorite samples (Figure 14.20 [63]).

-log σ [S cm -1 ] Ea, eV

(a) (b)

2

4 1.4

1

1.2

6

3

1.0

8

3

1

0.8

2

10

0.6 0

0 0.1 0.2 0.3 x

0.1 0.2 0.3 x

Figure 14.20 Concentration dependences of the conductivity (log ) at 500 K and of the
conductivity activation energy for Ca 1x R x F 2þx solid solutions. R - La(1), Gd(2), Lu(3).
(Reprinted with permission from [63] Copyright (2006) Pleiades Publishing Inc.)