Local structure order around Ni in Hf‒Cu‒Ni glassy ribbons: XANES and EXAFS study at Ni K‒edge

This work has investigated the formation of the local structure order around Ni in Hf‒Cu‒Ni glassy ribbons by employing X‒ray absorption near edge structure (XANES) and extended X‒ray absorption fine structure (EXAFS) spectroscopy at Ni K‒edge. XANES probed 1s to 4p transition at the shoulder of the spectra. The main peak of the spectra corresponds to the 1s to 4p dipole selection rule. The magnitude of the first peak of the EXAFS signal, belonging to the first coordination shell of Ni, decreased with an increase in Ni concentration. The coordination number (CN) of Ni/Cu atoms increases, whereas that of Hf atoms decreases with increasing Ni concentration. The first peak of Hf57Cu11Ni32 (Hf57), Hf59Cu18Ni23 (Hf59), and Hf60Cu21Ni19 (Hf60) is dominated by Ni–Ni and Ni–Cu pair. A nearly linear decrease in atomic distances of Ni‒Hf pair is observed with an increase in CN of Ni/Cu, thereby indicating atomic re‒arrangement around the central absorbing atom. Hf57 with large CN of Ni/Cu atoms has shown the most negative PHS (product of enthalpy of chemical mixing and normalized mismatch entropy) and large supercooled liquid region. This work reflects that the CN of an element strongly influences the glass formation ability of an alloy.