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The Binary Bi-Rh Phase Diagram: Stable and Metastable Phases.
Peter Kainzbauer1, Klaus W Richter1, Herbert Ipser1
1University of Vienna, Faculty of Chemistry, Department of Inorganic Chemistry - Functional Materials, Althanstrasse 14, 1090 Vienna, Austria.
Journal of Phase Equilibria and Diffusion
|January 31, 2020
Summary
This study reinvestigated the bismuth-rhodium phase diagram, refining phase boundaries and temperatures. A new phase, BiRh0.81, was discovered, and the metastability of Bi3Rh was confirmed.
Area of Science:
- Materials Science
- Solid State Chemistry
- Crystallography
Background:
- The binary bismuth-rhodium (Bi-Rh) system's phase diagram requires detailed investigation, particularly concerning the BiRh phase and its thermal behavior.
- Accurate phase diagrams are crucial for understanding material properties and developing new alloys.
Purpose of the Study:
- To reinvestigate the Bi-Rh phase diagram between 23 and 60 at.% Rh.
- To refine the phase boundaries and peritectic decomposition temperature of the BiRh phase.
- To confirm existing phases and identify new ones within the Bi-Rh system.
Main Methods:
- Powder X-ray diffraction (XRD) and high-temperature powder XRD were employed for phase identification and structural analysis.
- Differential thermal analysis (DTA) and scanning electron microscopy (SEM) were used to determine thermal events and microstructural features.
Main Results:
- The phase boundaries of BiRh at 750 °C and its peritectic decomposition temperature were refined.
- The existence of Bi4Rh and two modifications of Bi2Rh (α and β) was confirmed.
- A new orthorhombic phase, BiRh0.81 (MnP structure type, Pmna), was discovered.
- The previously reported stable Bi3Rh phase was found to be metastable.
- Revised peritectic reaction temperatures were determined: L + Rh ↔ BiRh at 979 °C and L + BiRh ↔ β-Bi2Rh at 785 °C.
Conclusions:
- The Bi-Rh phase diagram has been more accurately defined, with refined phase boundaries and reaction temperatures.
- The discovery of BiRh0.81 and the confirmation of Bi3Rh metastability provide new insights into the Bi-Rh system.
- The transition temperature between α-Bi2Rh and β-Bi2Rh is significantly influenced by the presence of Bi3Rh and BiRh0.81.
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