Nickel acetylacetonate was thermally decomposed in oleylamine under inert atmosphere. Nanocrystals of two cubic phases and a hexagonal phase appeared. The phases were identified using X-ray diffraction, laboratory X-ray photoelectron spectroscopy (XPS), and hard-X-ray photoelectron spectroscopy (HX-PES). The hexagonal phase was a nickel carbide, Ni3C, which had been often identified as a hexagonal close-packed metallic nickel. One cubic phase was a face-centered metallic nickel, and the other cubic phase was proposed as a novel cubic nickel carbide, which was characterized as an intermediate product of the carbidization of metallic face-centered cubic Ni to the hexagonal nickel carbide.

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Bulk sensitive x-ray spectroscopy is performed to systematically study the effect of substitution on the valence transition in strongly correlated Yb compounds, such as Y 0.1 Yb 0.9 InCu 4 , YbInCu 4 , and YbIn 0.88 Ag 0.12 Cu 4 , and is compared with complementary magnetic-susceptibility results. High-resolution x-ray absorption spectroscopy with partial fluorescence yields mode and resonant x-ray emission spectroscopy is used to measure the valency change as a function of temperature. The valency change determined from spectroscopy exactly follows the temperature evolution of the magnetic susceptibility. The results confirm first-order transitions in Y 0.1 Yb 0.9 InCu 4 and YbInCu 4 , while YbIn 0.88 Ag 0.12 Cu 4 exhibits a continuous mixedvalence transition. The present results are in agreement with the mean-field Anderson lattice model theory of Goltsev and co-workers ͓Phys. Rev. B 63, 155109 ͑2001͒; J. Phys.: Condens. Matter 17, S813 ͑2005͔͒, which includes the role of local deformations and Kondo volume collapse in the valence transition.