In this paper, diamond crystallization from carbonyl nickel powders is investigated in detailed by temperature gradient growth (TGG) at high pressure (6.0-6.5 GPa) and high temperature (1350-1430 degrees C) conditions. We find that the synthesis condition for diamond crystallization is higher than that of the conventional Fe-Ni catalyst medium. The morphology of the diamond synthesized from carbonyl nickel powders tends to an irregular shape. Furthermore, Fourier transform infrared (FTIR) measurements indicate that nitrogen atoms simultaneously exist in the synthesized diamond in the forms of A-centers and C-centers. We hope that our paper can provide valuable information and clues to study the incorporation of nitrogen impurity into natural diamond structure. (C) 2012 Elsevier B.V. All rights reserved.