Electric fields produced by a charge density in ionic crystals

Spati all y ex ten ded de fec ts s uc h a s th e F ce nt e r give rise to a n effective defec t cha rge de nsit y whI c h may produ ce im po rtan t pola ri za tio ns in th e c rys ta l.T he electric fi eld in the c rystal de pe nd s upo n these jnduced dipoles.Latti ce summa tio ns for th e contribution to th e elec tri c fi eld whic h arises fro m ioni c shell s ce nte red about th e defec t a re e va lua ted fo r th e NaC I a nd CaF, la ttice stru ctu res.