Indirect phase transition of refractory nitrides compounds of: TiN, ZrN and HfN crystal structures Eric K.K. Abavare a,⇑ , Michael K.E. Donkor a , Samuel N.A. Dodoo a , Osei Akoto b , Francis K. Ampong a , Bright Kwaakye-Awuah a , Robert K. Nkum a a Department of Physics, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana b Department of Chemistry, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana article info Article history: Received 7 February 2017 Received in revised form 27 March 2017 Accepted 8 April 2017 Keyword: Indirect phase transition and phonons abstract The static and dynamical phase stabilities of refractory nitrides based on plane wave calculation in the framework of generalised gradient approximation (GGA) are reported in this work. The calculation reveals that the postulated zinc blende (B3) phase is statically and dynamically stable unlike the cesium chloride (B2) because of an appearance of imaginary modes in the phonon spectra which prevents the formation of this crystal phase similar to the corresponding carbides. The soft modes of the phonon bands were explored over a temperature range of 280–350 K. The indirect phase transition pressures from the zinc blende to the cesium chloride structure are about 10-, 8-, and 7-fold lower compared with the direct transformation from the ground state rock-salt structure to the B2 phase of TiN, ZrN and HfN respectively. The calculated electronic partial density of states show strong hybridization at the gap region and that all the crystal phases are metallic. Again, the phonon calculation showed an appearance of phonon gap for the rock salt and the zinc blende phases but collapsed in the B2. Ó 2017 Elsevier B.V. All rights reserved. 1. Background Transition metal carbides and nitrides (carbonitrides) crystal- lizes into rock salt or the sodium chloride (B1) structure called refractory compounds [1,4] and belong to the space group Fm  3 m [2,3] (No. 225) with high binding energies resulting in high melting points [5]. The compounds physical properties are distinct of metal, very strong like diamond and considered as high temper- ature ceramics. The bonding [6] of the carbonitrides is as an admix- ture of metallic, ionic and covalent mechanisms which determine their unique properties. These attributes make the compounds interesting scientifically and technological attractive. The rele- vance of the refractory compounds to industry is enviable and interest in them keep growing. The use of these compounds are found in the protective and reactive coatings of nano composites [7], tools cutting, abrasives and even in microelectronics [8] where they are used as conductive barrier for metals contacts and active devices; here their electronic structures are explored in high tem- perature and pressure environments [9–11]. These compounds have widely been studied both experimentally [12–16] and theo- retically [6,17–19] and the research effort keeps increasing. Demkowicz et al. [20] group employed bulk diffusion couple experiments to study the chemical reactivity of the carbonitrides of Ti and silicon carbide relative to palladium and rhodium in the temperature regime of 1600  C. Similarly, the chemical reactivity of SiC-Pb coated fuel cells was previously explored by earlier work- ers [21,22] with respect to fuel application. Because SiC is very sus- ceptible to degradation by palladium, the use of carbonitrides as substitutes is seen as plausible candidates for fuel coating since they are gentle on Pd [23–25]. In similar related application, advanced fuels for the next generation gas-cooled fast neutron- spectrum reactors have been suggested to make use of other car- bonitrides ceramics instead of silicon carbide in fuel cell coating or ‘‘inert matrix” fuel materials [25,26]. Clearly, refractory compounds are superior materials for use in advanced industrial applications such as in optoelectronics and aerospace and depends on how stable the materials are to hostile conditions. The phase transition of TiC around 18 GPa from B1 to R phase was reported by Dubrovinskaia et al. [27] while Winkler et al. suggested that no phase transition in the B1 titanium carbide up to 26 GPa [28] exist; meanwhile no such report has been pre- sented for TiN. It has been conjectured that there is high probabil- ity for refractory carbonitrides to transform from the ground state NaCl(B1) to CsCl (B2) (space group Pm  3 m) [2,29] under high pressure. The transformation process is very similar to the http://dx.doi.org/10.1016/j.commatsci.2017.04.038 0927-0256/Ó 2017 Elsevier B.V. All rights reserved. ⇑ Corresponding author. E-mail addresses: eabavare@yahoo.com, ekkabavare.cos@knust.edu.gh (E.K.K. Abavare). Computational Materials Science 137 (2017) 75–84 Contents lists available at ScienceDirect Computational Materials Science journal homepage: www.elsevier.com/locate/commatsci