Electron doping of the layered nickelate La$_4$Ni$_3$O$_{10}$ by aluminum substitution: A combined experimental and DFT study

TL;DR

This study investigates how aluminum substitution affects the electronic, magnetic, and structural properties of La4Ni3O10, revealing significant changes in conductivity and magnetic behavior through combined experimental and DFT analyses.

Contribution

It provides new insights into electron doping effects in layered nickelates by combining experimental synthesis, characterization, and DFT calculations to understand property modifications.

Findings

Resistivity shifts from metallic to semiconducting with Al doping.

No long-range magnetic order detected despite doping.

Metal-to-metal transition persists up to 0.15 Al-level.

Abstract

The physical properties of La$_4$Ni$_3$O$_{10}$ with a 2D-like Ruddlesden-Popper-type crystal structure are extraordinarily dependent on temperature and chemical substitution. By introducing Al$^{3+}$ atoms ($x$) randomly at the Ni-sites, the average oxidation state for the two non-equivalent Ni-cations is tuned and adopt values below the average of +2.67 in La$_4$Ni$_3$O$_{10}$. La$_4$Ni$_{3-x}$Al$_x$O$_{10}$ is a solid solution for $x=0.00$ to 1.00, and are prepared by the citric acid method. The samples adopt a slightly distorted monoclinic structure (P21/a), evidenced by peak broadening of the (117) reflection. We report on a remarkable effect on the electronic properties induced by tiny amounts of homogeneously distributed Al-cations, with clear correspondence between resistivity, magnetization, diffraction, and DFT data. DFT shows that electronically there is no significant difference between the non-equivalent Ni atoms and no tendency towards any Ni$^{3+}$/Ni$^{2+}$ charge ordering. The electron doping via Al-substitution has a profound effect on electric and magnetic properties. The resistivity changes from metallic to semiconducting with increasing band-gap at higher Al-levels, consistent with results from DFT. The metal-to-metal transition reported for La$_4$Ni$_3$O$_{10}$, which is often interpreted as a charge density wave, is maintained until $x = 0.15$ Al-level. However, the temperature characteristics of the resistivity change already at very low Al-levels (below 0.03). A coupling of the metal-to-metal transition to the lattice is evidenced by an anomaly in the unit cell dimensions. No long-range magnetic order is detected by powder neutron diffraction. The introduction of the non-magnetic Al$^{3+}$ changes the Ni$^{3+}$/Ni$^{2+}$ ratio and is likely to block double-exchange pathways by means of -Ni-O-Al-O-Ni- fragments into the network of corner shared octahedra with the emergence of possible short-range order in ferromagnetic like islands.