Abstract: There is provided a process for producing LiMXO4, comprising the steps of reacting a source of lithium, a source of M, and a source of X together, in a melted state at a reaction temperature between 900 to 1450 C, in the presence of an excess of (A) a solid-solid reducing couple having an oxygen partial process at equilibrium (pO2) comprised between 10?8 and 10?15 atm at said reaction temperature according to an Ellingham-Richardson diagram for oxides, or (B) one component of the solid-solid reducing couple together with a gas-gas reducing couple having an oxygen partial pressure equilibrium (pO2) between 10?8 and 10?15 atm at said reaction temperature according to an Ellingham-Richardson diagram of oxides, and under thermic equilibrium and thermodynamic equilibrium. There is also provided a LiMXO4 melt-solidified product free from off-composition impurities.