Journal of Alloys and Compounds 366 (2004) 15–20 Plutonium chalcogenides and pnictides: pressure induced phase transition and elastic properties Vipul Srivastava, Sankar P. Sanyal ∗ Condensed Matter Physics Laboratory, Department of Physics, Barkatullah University, Bhopal 462 026, India Received 29 April 2003; received in revised form 8 July 2003; accepted 8 July 2003 Abstract We have investigated the structural and elastic properties of three plutonium mono-chalcogenides (PuX; X = S, Se, Te) and three mono-pnictides (PuY; Y = As, Sb, Bi) using an interionic potential theory with modified ionic charge, at high pressure. This method has been found quite satisfactory in the case of cerium mono-chalcogenides and mono-pnictides. The calculated equation of state, phase transition pressure, and bulk modulus agree well with the experimental findings. We have also reported the second order elastic constants (SOEC) for these Pu compounds, for the first time. A comparison of the properties of chalcogenides and pnictides of shifted homolog pair Ce–Pu, is also presented. © 2003 Elsevier B.V. All rights reserved. Keywords: Plutonium compounds; High pressure; Phase transition; Elastic properties 1. Introduction Most of the rare earth (RE) mono-chalcogenides and pnic- tides [1] crystallize in NaCl type structure at ambient pres- sure and their f-electrons are localized. In the case of ac- tinide compounds, the RE ion has electronic configuration 5f n (6d7s) m . Under the application of pressure, these com- pounds lead to structural change and their valance changes to 5f n-1 (6d7s) m+1 . Extensive investigations have been car- ried out to understand the role played by the f-electrons in RE compounds. Many of them exhibit non-integer va- lence at high pressure and show different structures and properties and can be interpreted in terms of mixed va- lence compounds, arising from unstable f-orbital [2]. The actinide compounds can be divided into two groups; one belonging to localized 5f-electrons and other having itiner- ant 5f-electrons. The delocalization or itinerancy depends on the actinide–actinide distance under pressure [3]. The local- ized f-electrons at ambient pressure also show itinerancy in the same compound at high pressure. Such itinerant behav- ior can be seen in both lanthanide and actinide compounds and influences the structural phase transition. Benedict [1] ∗ Corresponding author. E-mail address: spsanyal@sancharnet.in (S.P. Sanyal). have reported a comparative study of homolog (compounds of lanthanide and actinide series with equal f-count, i.e. 4f n and 5f n ) and shifted homolog (compounds of lanthanide and actinide series with shifted f-count, i.e. 4f n and 5f n+4 ) with respect to their structural transition pressure and bulk modu- lus. Shifted homology initially proposed by Johansson [4] to explain the similarities between lanthanide 4f n and actinide 5f n+4 compounds. In this regard, a comparative study of the high-pressure properties of plutonium compounds with those of the cerium compounds will be useful for under- standing the role of f-electrons. It is revealed from the literature that the plutonium chalco- genides, PuX (X = S, Se, Te) and pnictides, PuY (Y = As, Sb, Bi) crystallize in NaCl type structure [1]. Amongst PuX and PuY compounds, PuS does not show any kind of phase transformation from its ambient NaCl structure up to 60 GPa [5], while PuSe [6] exhibits double phase change in the pressure range up to 47 GPa. Around 18 GPa, the B 1 type structure undergoes a second order phase transition to a rhombohedral phase and finally it transforms to the B 2 type structure around 35 GPa with a volume change of 11%. PuTe undergoes B 1 → B 2 transition between 15 and 19 GPa [7] with 9% volume reduction. In the mono-pnictides of pluto- nium, PuAs shows B 1 → B 2 transition around 35 GPa [8] while PuSb undergoes B 1 → B 2 transition at 18 GPa and 0925-8388/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0925-8388(03)00692-3