[en] The characteristics of a RF plasma for the crystal growth of nitrides with high dissociation pressures are described. The electrical behavior measured with a new ammeter is sensitive to both gas composition and ambient pressure. A VN rod was melted under optimum conditions of 400 torr in an Ar-N₂ mixed plasma to demonstrate that the present crystals have nearly the same composition as those obtained by RF induction heating under 10 atm of nitrogen. This is direct evidence of chemical dissociation of nitrogen from the melt being suppressed by means of the RF plasma gas