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The Thermodynamic Assessment of the Binary System Bi-Rh Ondrˇej Zobacˇ1 • Alesˇ Kroupa1

Submitted: 25 August 2020 / in revised form: 2 November 2020 / Accepted: 7 November 2020 Ó ASM International 2020

Abstract The Bi-Rh binary phase diagram was modelled by CALPHAD approach for the first time. The modelled phase diagram is based mainly on recently published experimental phase diagrams. Very good agreement with the experimental results was reached for the Bi-Rh phase diagram and for the calculated thermodynamic properties, namely the standard enthalpy of mixing of the BiRh phase at 25 °C. Keywords Bi-Rh system  binary phase diagram  CALPHAD approach  first assessment

presented by Kainzbauer et al.,[1] it was possible to construct first CALPHAD (CALculation of PHAse Diagram) type thermodynamic description of the Bi-Rh system. Bi-Rh system investigations were initiated by the interest in the superconductivity phenomenon in Zhuravlev and Zhdanov Ref 2 and by using of Rh as a stabilizing element of the unquenchable a-BiMn phase which is interesting as a ferromagnetic material presented by Lee et al.[3] The recently published experimental phase diagrams presented by Weitzer et al.[4] (Fig. 1a) and by Kainzbauer et al.[1] are shown on Fig. 1(b). A prior CALPHAD-based thermodynamic assessment of the phase diagram Bi-Rh had not been published.

1 Introduction 2 Literature Review Phase diagrams are important for the development of new materials and the study of their properties. Detailed knowledge about the coexistence and stability of phases in stable or metastable equilibrium significantly rationalizes design and consequent development of required materials properties. As experimental studies of multicomponent phase diagrams are very time consuming, the semiempirical CALPHAD type modelling of multicomponent phase diagrams is a very useful tool for the materials development. Robust and reliable thermodynamic descriptions of basic binary systems are crucial for the modelling of multicomponent systems. Thanks to the new experimental phase equilibria results of the Bi-Rh system that were

& Ondrˇej Zobacˇ [email protected] 1

Academy of Science, Institute of Physics of Materials, Zˇizˇkova 22, Brno 616 00, Czech Republic

2.1 Available Experimental Information The oldest experimental investigations of phases in the BiRh system were published in 1900 by Ro¨ssler[5] (Bi4Rh) and Wo¨hler and Metz[6] (Bi2Rh). First experimental phase diagram was published by Rode,[7] followed by Hansen et al.[8] The Bi-Rh alloys were studied intensively with a special focus on the superconducting properties of intermetallic phases by several authors.[2,9–12] A more refined phase diagram was constructed by Kuzmin et al.[11,12] and by Ross and Hume-Rothery.[13,14] Newly assessed the BiRh phase diagram was published by Predel.[15] Okamoto[16] published experimental assessment of the system based on experimental data published by Weitzer et al.[4] Kainzbauer et al.[1] recently published very complex experimental study of the Bi-Rh system using combina