Controlling Dimensionality in the Ni–Bi System with Pressure

The discovery of new layered materials is crucial for the development of novel low-dimensional materials. Here, we report in situ high-pressure studies of the quasi-one-dimensional (1D) material NiBi3, revealing the formation of a new layered intermetallic phase, NiBi2. In situ diffraction data enabled us to solve the structure of NiBi2, which crystallizes in the same structure type as PdBi2, adding to a growing number of examples in which first-row transition-metal binary systems form structures at high pressure comparable to the ambient-pressure structures of their second-row congeners. Based upon the diamond anvil cell reactions, we initiated scale-up reactions in a multianvil press and isolated bulk NiBi2. Isolating a bulk sample enabled us to evaluate prior theoretical predictions of phase stability for NiBi2. Our findings of metastability within this phase are contrary to previous predictions, recommending continuing research into this phase. The dimensionality of the building units seems to vary as a function of synthesis pressure in the Ni–Bi system, being quasi-1D at ambient pressures (NiBi3), quasi-two-dimensional at ∼14 GPa (NiBi2), and three-dimensional at ∼39 GPa (β-NiBi). This observation represents the first demonstration of dimensionality control in a binary intermetallic system via application of pressure.