High-pressure Phase Transition and Properties of Cu₃N: An Experimental and Theoretical Study

Aron Wosylus (1) , Ulrich Schwarz (1) , Lev Akselrud (1) , Matt Tucker (2) , Michael Hanfland (3) , Rabia Kaneez (4) , Christine Kuntscher (1) , Jörg von Appen (5) , Richard Dronskowski (1) , Dieter Rau (6) , Rainer Niewa (1)

1 CPfS - Max-Planck-Institut für Chemische Physik fester Stoffe
2 RAL - STFC Rutherford Appleton Laboratory
3 ESRF - European Synchrotron Radiation Facility
4 Institut für Physik
5 IAC RWTH - Institute of Inorganic Chemistry [Aachen]
6 Institut für Anorganische Chemie

In-situ X-ray and neutron diffraction investigations on Cu₃N indicate the onset of a high-pressure phase transition at about 5 GPa. The tetragonal cell parameters of the high-pressure phase reveal a discontinuous volume decrease of about 20 %. The phase transition is reversible, with a hysteresis of about 2 GPa. Subsequent ex-situ investigations in a multi-anvil press evidence a reversible re-formation of ambient pressure Cu₃N from XRD patterns. The structure refinement with N atoms disordered in distorted octahedral voids of a tetragonal body-centered Cu-substructure leads to an occupation of approximately 1/3 and thus to a composition of Cu₃N_1.0(1). Optical absorption measurements (IR-VIS) up to 10 GPa indicate a semiconductor–metal transition. Density-functional based total energy calculations concerning the proposed high-pressure phase of Cu₃N support strongly the experimental findings of a pressures-induced phase transition above 6 GPa to a structure with a Cu tetragonal body-centered sublattice and nitrogen atoms in distorted octahedral voids. However, the calculations identify a need for an ordered alternative to provide the tetragonal distortion within the range of the observed c/a-ratio. The resulting lattice parameters and the transition pressure fit with the measured data. For the case of an ordered occupation of the Cu bct octahedral voids, all observed properties are in good agreement with the calculations.

Mots clés: Physical Sciences

Aron Wosylus, Ulrich Schwarz, Lev Akselrud, Matt Tucker, Michael Hanfland, et al.. High-pressure Phase Transition and Properties of Cu₃N: An Experimental and Theoretical Study. Journal of Inorganic and General Chemistry / Zeitschrift für anorganische und allgemeine Chemie, 2009, 635 (12), pp.1959. ⟨10.1002/zaac.200900369⟩. ⟨hal-00514959⟩