Charge ordering and magnetism in the intermetallic oxides R₅Pb₃O (R = La-Sm)

The R₅Pb₃O family crystallizes in an interstitial derivative of the tetragonal Cr₅B₃ structure, in contrast to many hexagonal R₅Pb₃Z (Z = B, C, P) compounds. This structure features R-Pb chains along the c-axis. Despite being known for many years [1, 2], this family has remained largely unexplored until recently [3], with no physical properties reported for R = Pr-Sm compounds. In this talk, we present transport, magnetization, and diffraction measurements for R₅Pb₃O single crystals. Our experimental data, in agreement with theoretical calculations, support that the R₅Pb₃O (R = La and Ce) series hosts an electron-phonon coupling driven charge density wave (CDW) at low temperatures. The CDW ordering temperature is suppressed by more than 100 K by the La to Ce substitution, and X-ray diffraction indicates that the CDW is fully suppressed for R = Pr-Sm. Magnetic measurements reveal that the R = Pr-Sm members have ferrimagnetic structures with anomalously large coercive fields. Finally, high-pressure X-ray diffraction indicates structural transitions for the R = Pr-Sm, suggesting that the compression of R-Pb chains may stabilize new phases. 

[1] Guloy et al. Z. Anorg. Allg. Chem. 616.10 (1992). 

[2] Macaluso et al. Chem Mater. 16, 1560-1563 (2004). 

[3] Penacchio et al. Phys. Rev. B, accepted on 18 September 2025. doi: 10.1103/c1qw-ddfn