Solid solutions based on Na 7 (InP 2 O 7 ) 4 PO 4 and Na 3 In 2 (PO 4 ) 3 , where chromium, iron, and man ganese substitute for indium, have been prepared. When chromium and iron substitute for indium in Na 7 (InP 2 O 7 ) 4 PO 4 , a continuous solid solution series exists. When manganese substitutes for indium, it enters the compound in the oxidation state +3. The substitution of chromium for indium in Na 3 In 2 (PO 4 ) 3 occurs within the range from 0.11 to 0.74 (mol/mol), and that of iron for indium, from 0.09 to 0.62 (mol/mol). When manganese substitutes for indium, it enters the structure of the crystalline phase in insignificant amounts as a two charged cation.