Structural insights into thermal behavior and vibrational properties of Ni5P4

First-row transition metal (Me) phosphides are the cost-effective materials in sustainable chemistry, including applications in hydrogen evolution reaction and the development of alkaline-metal-ion batteries. However, thermal behavior and vibrational properties of transition metal phosphides have been poorly studied. We report data on Ni₅P₄, one of the technologically demanded nickel phosphides, which was investigated by means of scanning electron microscopy, electron microprobe analyses, electron backscatter diffraction, Raman spectroscopy combined with Density Functional Theory and single-crystal X-ray diffraction (over the temperature range of 163–773 K). For the first time we determine its thermal expansion coefficient (α_V = 19 × 10⁻⁶ K⁻¹) based on single crystal data, and showed that the crystal structure of Ni₅P₄ undergoes maximum expansion perpendicular to the c axis, and minimum expansion along the c axis. Ni₅P₄ has clear Raman spectrum (18 peaks, the most intense and best resolved peaks are 143, 203, 238, 314, 414, 425 and 476 cm⁻¹). Our results evidence that quasi-metallic transition metal phosphides having Me/P ratio >1 can produce the quality Raman spectra applicable for their characterization.