Direct observation of β-TaH phase precipitation in tantalum endash hydrogen solid solution

An ordered β-Ta2H tantalum hydride precipitate and a disordered α-Ta endash H solid solution matrix have been observed directly by field ion microscopy and analyzed by atom probe analysis. The ordered and disordered field ion images have been explained by the electronic transition rate in the theory of field ionization. On the other hand, we found surprisingly that the field evaporation voltage dramatically decreased to approximately one half of its original evaporation voltage as the evaporation of the precipitate moves toward the phase boundary, which may due to the effects of the interface energy. copyright 1996 American Vacuum Society