Single crystals of the metallic Ruddlesden-Popper trilayer nickelates $R_4{\mathrm{Ni}}_3{\mathrm{O}}_{10}$ ($R=\mathrm{La},\mathrm{Pr}$) were successfully grown using an optical-image floating zone furnace under oxygen pressure $\left(p{\mathrm{O}}_2\right)$ of 20 bar for ${\mathrm{La}}_4{\mathrm{Ni}}_3{\mathrm{O}}_{10}$ and 140 bar for ${\mathrm{Pr}}_4{\mathrm{Ni}}_3{\mathrm{O}}_{10}$. A combination of synchrotron and laboratory x-ray single-crystal diffraction, high-resolution synchrotron x-ray powder diffraction and measurements of physical properties revealed that $R_4{\mathrm{Ni}}_3{\mathrm{O}}_{10}$ ($R=\mathrm{La},\mathrm{Pr}$) crystallizes in the monoclinic $P{2}_1/a$ ($Z=2$) space group at room temperature, and that a metastable orthorhombic phase (Bmab) can be trapped by postgrowth rapid cooling. Both ${\mathrm{La}}_4{\mathrm{Ni}}_3{\mathrm{O}}_{10}$ and ${\mathrm{Pr}}_4{\mathrm{Ni}}_3{\mathrm{O}}_{10}$ crystals undergo a metal-to-metal transition (MMT) below room temperature. In the case of ${\mathrm{Pr}}_4{\mathrm{Ni}}_3{\mathrm{O}}_{10}$, the MMT is found at 157.6 K. For ${\mathrm{La}}_4{\mathrm{Ni}}_3{\mathrm{O}}_{10}$, the MMT depends on the lattice symmetry: 147.5 K for Bmab vs 138.6 K for $P{2}_1/a$. Lattice anomalies were found at the MMT that, when considered together with the pronounced dependence of the transition temperature on subtle structural differences between Bmab and $P{2}_1/a$ phases, demonstrate a not insignificant coupling between electronic and lattice degrees of freedom in these trilayer nickelates.

• Received 7 April 2019
• Revised 6 June 2020
• Accepted 13 July 2020

DOI:https://doi.org/10.1103/PhysRevMaterials.4.083402