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 NiBi ₃ , revealing the formation of a new layered intermetallic phase, NiBi ₂ . In situ diffraction data enabled us to solve the structure of NiBi ₂ , which crystallizes in the same structure type as PdBi ₂ , 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 NiBi ₂ . Isolating a bulk sample enabled us to evaluate prior theoretical predictions of phase stability for NiBi ₂ . 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 (NiBi ₃ ), quasi-two-dimensional at ∼14 GPa (NiBi ₂ ), 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.