$La_3Pd_2NaO_9$: A High-Valent Insulating Palladate

TL;DR

This paper reports the synthesis and detailed characterization of a novel high-valent palladate, La3Pd2NaO9, revealing its crystal structure, insulating behavior, and magnetic properties, and suggesting potential for further exploration of palladates.

Contribution

First synthesis and structural analysis of La3Pd2NaO9, a high-valent palladate with unique properties, expanding the understanding of palladate materials.

Findings

La3Pd2NaO9 crystallizes in monoclinic P2_1/c space group.

The material exhibits insulating electrical behavior.

Magnetic measurements indicate paramagnetism likely due to high-spin Pd2+.

Abstract

A high-valent palladate, $La_3Pd_2NaO_9$, has been synthesized for the first time. Single crystals with dimensions of 20 ${\mu}$m on edge were successfully grown using the flux method at 420 $^o$C and 70 bar oxygen pressure. Energy dispersive spectroscopy (EDS) and inductively coupled plasma mass spectroscopy (ICP) measurements show that the atomic ratio of La: (Pd+Na) is 3: 3 and Pd: Na is 2: 1. X-ray photoelectron spectroscopy (XPS) measurements show that the oxidation state of Pd is dominated by +4. Synchrotron X-ray single-crystal diffraction measurements revealed that this material crystallizes in the monoclinic $P2_1/c$ space group with charge ordering of Na and Pd. Real-space imaging via scanning transmission electron microscopy (STEM) confirmed the crystal structure and revealed excellent sample homogeneity. Electrical resistivity measurements show an insulating behavior. Magnetic measurements show an unexpected paramagnetic behavior, which probably originate from a small fraction of high-spin Pd$^{2+}$ evidenced by XPS. The successful growth of $La_3Pd_2NaO_9$ single crystals with a high-valent oxidation state of Pd offers an approach for exploring interesting palladates, including potential bilayer Ruddlesden-Popper palladates analogous to the high temperature superconducting $La_3Ni_2O_7$.