Charge density wave in intermetallic oxides R$_5$Pb$_3$O (R = La and Ce)

TL;DR

This study reports the discovery of charge density wave order in R$_5$Pb$_3$O intermetallic oxides (R=La, Ce), revealing structural phase transitions and electron-phonon interactions, with potential for exploring competing orders in oxides.

Contribution

First detailed characterization of R$_5$Pb$_3$O compounds, identifying CDW order and structural transitions, expanding understanding of intermetallic oxides with rare-earth elements.

Findings

Charge density wave observed in La and Ce variants.

Structural phase transition at 260 K (La) and 145 K (Ce).

CDW ordering temperature is highly pressure-sensitive.

Abstract

The R$_5$Pb$_3$O family was discovered decades ago, but has remained largely unexplored. Here, we report single crystal growth and basic characterization for the La and Ce members of this family. At room temperature, these compounds adopt a tetragonal structure (I4/mcm), where R and Pb atoms form linear chains along the c-axis. We identify a second-order structural phase transition at 260 K and 145 K for R = La and Ce, respectively. Single crystal X-ray diffraction reveals a lattice modulation below the transition temperature, resulting in R-Pb pairs in the z direction. The broken symmetry in the low-temperature phases results in a primitive structure with space group P4/ncc. Transport and diffraction measurements, in agreement with density functional theory calculations, support that the R$_5$Pb$_3$O (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, suggesting high pressure-sensitivity. Therefore, this family offers the potential for investigating competing orders in oxides, with heavier rare-earth members still to be explored.