Discovery of Two Polymorphs of TiP(4)N(8) Synthesized from Binary Nitrides

TiP(4)N(8) was obtained from the binary nitrides TiN and P(3)N(5) upon addition of NH(4)F as a mineralizer at 8 GPa and 1400 °C. An intricate interplay of disorder and polymorphism was elucidated by in situ temperature‐dependent single‐crystal X‐ray diffraction, STEM‐HAADF, and the investigation of annealed samples. This revealed two polymorphs, which consist of dense networks of PN(4) tetrahedra (degree of condensation κ=0.5) and either augmented triangular TiN(7) prisms or triangular TiN(6) prisms for α‐ and β‐TiP(4)N(8), respectively. The structures of TiP(4)N(8) exhibit body‐centered tetragonal (bct) framework topology. DFT calculations confirm the measured band gaps of α‐ and β‐TiP(4)N(8) (1.6–1.8 eV) and predict the thermochemistry of the polymorphs in agreement with the experiments.