A DFT study of structural, elastic and lattice dynamical properties of Fe 2 Zr and FeZr 2 intermetallics Kawsar Ali a, b , P.S. Ghosh a, b, * , A. Arya a, b a Materials Science Division, Bhabha Atomic Research Centre, Mumbai, 400085, India b Homi Bhabha National Institute, Mumbai, 400094, India article info Article history: Received 6 January 2017 Received in revised form 12 June 2017 Accepted 13 June 2017 Available online 15 June 2017 Keywords: Thermodynamic properties Fe-Zr alloys Thermal conductivity Phonons abstract We report plane-wave based density functional theory (DFT) investigation of structural, elastic and lattice dynamical properties of Fe-rich C15-Fe 2 Zr and Zr-rich FeZr 2 intermetallic compounds. These in- termetallics dominantly appear in the Fe-Zr alloys which are potential candidates for immobilization of nuclear metallic waste. The calculated elastic constants and phonon dispersions show that both phases are mechanically and dynamically stable. The calculated bulk moduli as a function of temperature show that the Fe-rich C15 phase is less compressible and also less sensitive to temperature than the Zr-rich C16 phase. Furthermore, the C15-Fe 2 Zr phase has a lower thermal expansion co-efficient but higher thermal conductivity as compared to the C16-FeZr 2 phase; while the heat capacities (C P and C V ) of both the phases are almost identical above 450 K. © 2017 Elsevier B.V. All rights reserved. 1. Introduction Iron-Zirconium alloys play an important role in the nuclear in- dustry. Zr-rich Fe-Zr alloys are used as structural materials for light and heavy water based thermal reactors due to their low neutron absorption cross section and good mechanical and corrosion properties [1e3]. Zr-rich alloys, e.g., Zr-8 Stainless steel (SS) and Fe- rich alloys, e.g., SS-15 Zr alloys are promising candidates for immobilization of metallic solid waste originating after the reprocessing of spent nuclear fuel [4,5]. The domain of applications of Fe-Zr alloys and their ternary derivatives is not limited to the nuclear industry, as in Fe based aluminides, the presence of inter- metallic phases provides an additional strength which makes these alloys a suitable structural material for high temperature applica- tions [6e8]. Fe-Zr alloys are also excellent glass formers over a broad range of compositions [9,10] and the presence of interme- tallic phases acts as a storage material for hydrogen and its isotopes [11,12]. Furthermore, Zircaloy-2 and Zircaloy-4 alloys, which are used as structural and cladding materials in light and heavy water based thermal reactors, contain some amount of Fe and due to its fast diffusion and very low solubility in a-Zr [13,14], several intermetallic compounds, viz., hexagonal and cubic (Fe,Cr) 2 Zr Laves phases, tetragonal (Fe,Ni)Zr 2 phase and orthorhombic FeZr 3 are formed during different heat treatments [15e18]. The presence of Fe 2 Zr and FeZr 2 phases in SS-15 Zr and Zr-8 SS is prominent which in turn can incorporate the long living read- ionuclides present in the metallic waste [19e21]. In Fe-Zr binary phase diagram, three polymorphs of Fe 2 Zr, viz., cubic (C15), di- hexagonal (C36) and hexagonal (C14) phases and two poly- morphs of FeZr 2 , viz., a tetragonal (C16) phase and a cubic- structured phase, which only crystallizes in the presence of non- metals like O or N, have been observed [4,22,23]. Among the three polymorphs of Fe 2 Zr, the C15-phase has been shown experimen- tally to be the most stable phase under ambient conditions, while the other two phase are stable at high temperatures [22,23]. Similarly, the C16-FeZr 2 phase has been experimentally shown to be the most stable phase [22,24,25]. The evaluation of structural, mechanical and thermodynamic properties of C15-Fe 2 Zr and C16-FeZr 2 phases is crucial for estab- lishing their thermodynamic and elastic stability from the point of view of their potential use as metallic wasteforms in nuclear in- dustry. In our earlier publication, we calculated the ground state structural, mechanical and elastic properties of all the stable and metastable intermetallics of Fe-Zr system [26]. However, thermo- dynamic properties of Fe-Zr intermetallics have been insufficiently reported in the literature. Lück et al. [27] measured the constant pressure specific heat (C P ) of C14-Fe 2 Zr phase using differential * Corresponding author. Materials Science Division, Bhabha Atomic Research Centre, Mumbai, 400085, India. E-mail address: parthasarathi13@gmail.com (P.S. Ghosh). Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom http://dx.doi.org/10.1016/j.jallcom.2017.06.154 0925-8388/© 2017 Elsevier B.V. All rights reserved. Journal of Alloys and Compounds 723 (2017) 611e619