Off-center impurity atoms in crystals

Alkali halides

• Lithium in potassium chloride, KCl(Li)
• Fluorine in sodium bromide, NaBr(F)
• Fluorine in potassium iodide, KI(F)
• Fluorine in rubidium iodide, RbI(F)
• Copper in potassium chloride, KCl(Cu)
• Silver in rubidium chloride, RbCl(Ag)
• Silver in rubidium bromide, RbBr(Ag)

Wide-gap incipient ferroelectrics

• Lithium in potassium tantalate, KTaO₃(Li)
• Niobium in potassium tantalate, KTaO₃(Nb)
• Sodium in potassium tantalate, KTaO₃(Na)
• Calcium in strontium titanate, SrTiO₃(Ca)
• Lead in strontium titanate, SrTiO₃(Pb)
• Manganese in strontium titanate, SrTiO₃(Mn)

IV-VI narrow-gap semiconductors

• Germanium in lead telluride, PbTe(Ge)
• Germanium in lead selenide, PbSe(Ge)
• Germanium in tin telluride, SnTe(Ge)
• Sulphur in lead telluride, PbTe(S)
• Selenium in germanium telluride, GeTe(Se)
• Lead in germanium telluride, GeTe(Pb) - a new type of off-center impurity of large size
• Tin in germanium telluride, GeTe(Sn) - a new type of off-center impurity of large size

Other crystals

• Oxygen in silicon, Si(O) (so-called A-center in irradiated silicon)
• Nitrogen in diamond, C(N)