Binary Intermetallics in the 70 atom % R Region of Two R-Pd Systems (R = Tb and Er): Hidden, Obscured, or Nonexistent?

Thomas Bell,Anja-Verena Mudring,Volodymyr Smetana,Gerd H. Meyer

doi:10.1021/acs.inorgchem.0c01311

Thomas Bell, Anja-Verena Mudring + Show 2 more

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https://doi.org/10.1021/acs.inorgchem.0c01311

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Abstract

Although rare-earth-metal–transition-metal (R/T) phase diagrams have been explored extensively, our recent studies have uncovered new previously nonexistent binary intermetallics. These compounds belong to a narrow region between 70 and 71.4 atom % of the rare-earth metal but represent four different structure types. The binaries Tb7Pd3 and Er17Pd7 are compositionally approaching (less than 1 atom % difference) the previously reported R2.16Pd0.89 (R = Tb and Er), and apparently form by peritectoid transformation, thus, being hard to detect by fast cooling. Tb7Pd3 (1) crystallizes in the Th7Fe3 structure type (hP20, P63mc, a = 9.8846(4) Å, c = 6.2316(3) Å, Z = 2) while Er17Pd7 (2) belongs to the Pr17Co7 type being its second reported representative (cP96, P213, a = 13.365(2) Å, Z = 4). Er17Pd7 (2) is overlapping with the cubic F-centered Er2.11Pd0.89 (3b, Fd3̅m, a = 13.361(1) Å, Z = 32) with practically identical unit cell parameters but a significantly different structure. Electronic structure calculations confirm that heteroatomic R–T bonding strongly dominates in all structures; T–T bonding interactions are individually strong but do not play a significant role in the total bonding.

Highlights

In order to further explore cluster complex halides {TtRr}Xx with group 8−10 transition metals as the endohedral atom, a systematic study of the R/T/X systems (R = rare earth metal, T = transition metal, X = Cl, Br, and I) has been performed.[1−4]When the electronegativity of the halide increases, there is an increasing competition in the formation of cluster complex halide {TtRr}Xx versus intermetallic {TtRr} and salt RX3
Similar outcome has been observed for the synthesis targeting {CoPr3}Br3 leading to the formation of Co7Pr17.5 It is interesting to note that the corresponding binary intermetallic systems, Pr/Pt and Pr/Co, have been investigated thoroughly,[6] yet neither Pr4Pt3 nor Pr17Co7 had been identified during the initial phase diagram constructions
Two new rare earth-rich binary compounds with the late transition metal palladium, Tb7Pd3 (1, 70 atom % Tb) and Er17Pd7 (2, 70.8 atom % Er), have been observed during the exploration of rare-earth metal cluster complex halides with the endohedral transition metal atom Pd

Summary

■ INTRODUCTION

Our recent study on the Pr/Pt system showed that the application of various fluxes may lead to the discovery of hardly accessible or metastable intermetallics; they may be hidden or obscured and have been nonexistent to that point.[10] Both the Tb/Pd and Er/Pd systems have been explored since the 1950s exhibiting nine binary phases plus two hightemperature modifications each.[6,7] It is worth noting that both systems are almost identical excluding the newly explored region. The rare-earth halides were obtained via the ammonium chloride route from the respective oxide.[30,31] Due to the high sensitivity of some starting materials and products to moisture or air, all samples between 250 and 500 mg were weighed and loaded into tantalum ampules inside an argon-filled glovebox. Chemical bonding analysis was performed based on the crystal orbital Hamilton populations (COHP).[41]

■ RESULTS AND DISCUSSION

■ CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES