The electrochemical behavior of Zr4+ in potassium-free fused alkali fluorides has been studied in the temperature range of 773-1123 K. With an inert tungsten or molybdenum electrode, a well-defined oxydo-reduction wave was observed during cyclic voltammetry experiments. The reduction of Zr4+ is a single four-electron reversible step, and the process is diffusion controlled. Chronopotentiometry measurements give rise to the diffusion coefficient values of Zr4+ ions. For instance, a value 2.92 x 10(-5) cm(2) s(-1) was found at 1010 K. The reduction of Zr4+ ions was also studied using a nickel electrode for which Ni-Zr alloys formation was pointed out as revealed by cyclic voltammetry. The analysis of these deposits by scanning electron microscopy (SEM) and energy dispersive X-ray showed the presence of a multilayered Ni-Zr alloy with different Zr contents. On graphite electrodes, zirconium carbides have been evidenced on cyclic voltammograms and the formation of Zr metal was observed by SEM. (c) 2007 The Electrochemical Society.