The Wilson-Curtis equation In(alpha (an)) = Int (alpha (0)(an)) - b/d(2) re
lating the anion polarizability alpha (an) to the anion-cation distances d
in cubic NaCl-type alkali halides of the composition MX (M = Li, Na, K, Rb,
Ca; X = F, Cl, Br, I) is found to be valid for the family MF2 and M1-xRxF2
+x, crystals (M = Ca, Sr, Ba, Cd and R is a rare-earth metal) with the fluo
rite-type structure. (C) 2000 MAIK "Nauka/Interperiodica".