The substitution of sodium for calcium in the fluoroapatite Ca10-xNax(
PO4)(6-x)SO4)(x)F-2 has been investigated. For 0 less than or equal to
x less than or equal to 6, a solid solution is obtained. From solid s
tate Na-23 MAS-NMR spectroscopy, it is shown that for the high substit
ution ratios, the sodium ions go into me Ca-II sites only, whereas at
small contents they are distributed among various sites. As a conseque
nce a drastic increase of the ionic conductivity is observed for the s
mall amounts of sodium with a maximum at x=0.4. From impedance measure
ments with sodium conducting electrodes, we can attribute this increas
e of conductivity to sodium mobility. Upon increasing the sodium conte
nt, conductivity decreases again and becomes purely fluorine-type agai
n.