A method for manufacturing a molten material (the crystallized portion of which consists of a single crystalline phase), includes a) mixing raw materials so as to form a feedstock; b) melting the feedstock until a liquid mass reaches a temperature higher than the melting temperature Tf of the molten material obtained at the end of step e); c) cooling until the liquid mass is completely solidified to obtain a molten material, the amorphous phase of which is constitutes less than 80 wt % thereof; d) optionally crushing/grinding and/or performing selection by particle size on the molten material; e) optionally, heat-treating the molten material at a temperature which is an increment lower than the melting temperature of the molten material and is between Tf−800° C. (or 500° C.) and Tf−50° C., for a period of time in a reducing environment; and f) optionally, crushing/grinding and/or performing selection by particle size on said molten material.