Abstract
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.