High-Pressure Synthesis of the β-ZnN Nitride and the α-ZnN and β-ZnN Polynitrogen Compounds.

High-pressure nitrogen chemistry has expanded at a formidable rate over the past decade, unveiling the chemical richness of nitrogen. Here, the Zn-N system is investigated in laser-heated diamond anvil cells by synchrotron powder and single-crystal X-ray diffraction, revealing three hitherto unobserved nitrogen compounds: β-ZnN, α-ZnN, and β-ZnN, formed at 35.0, 63.5, and 81.7 GPa, respectively. Whereas β-ZnN contains the N nitride, both ZnN solids are found to be composed of polyacetylene-like [] chains. Upon the decompression of β-ZnN below 72.7 GPa, a first-order displacive phase transition is observed from β-ZnN to α-ZnN. The α-ZnN phase is detected down to 11.0 GPa, at lower pressures decomposing into the known α-ZnN (space group 3̅) and N. The equations of states of β-ZnN and α-ZnN are also determined, and their bulk moduli are found to be = 126(9) GPa and = 76(12) GPa, respectively. Density functional theory calculations were also performed and provide further insight into the Zn-N system. Moreover, comparing the Mg-N and Zn-N systems underlines the importance of minute chemical differences between metal cations in the resulting synthesized phases.