the invention relates to novel materials of the formula : a 1 - δ m 1 v m 2 w m 3 x m 4 y m 5 z o 2 wherein a is one or more alkali metals comprising sodium and / or potassium either alone or in a mixture with lithium as a minor constituent ; m 1 is nickel in oxidation state + 2 ; m 2 comprises a metal in oxidation state + 4 selected from one or more of manganese , titanium and zirconium ; m 3 comprises a metal in oxidation state + 2 , selected from one or more of magnesium , calcium , copper , zinc and cobalt ; m 4 comprises a metal in oxidation state + 4 , selected from one or more of titanium , manganese and zirconium ; m 5 comprises a metal in oxidation state + 3 , selected from one or more of aluminium , iron , cobalt , molybdenum , chromium , vanadium , scandium and yttrium ; wherein 0 ≦ δ ≦ 0 . 1 v is in the range 0 & lt ; v & lt ; 0 . 5 ; w is in the range 0 & lt ; w ≦ 0 . 5 ; x is in the range 0 ≦ x & lt ; 0 . 5 ; y is in the range 0 ≦ y & lt ; 0 . 5 ; z is ≧ 0 ; and further wherein v + w + x + y + z = 1 . such materials are useful , for example , as electrode materials in sodium ion battery applications .