High oxygen pressure floating zone growth and crystal structure of the layered nickelates R${}_4$Ni${}_3$O${}_{10}$ (R=La, Pr)

Abstract

Single crystals of the metallic Ruddlesden-Popper trilayer nickelates R${}_4$Ni${}_3$O${}_{10}$ (R=La, Pr) were successfully grown using an optical-image floating zone furnace under oxygen pressure (pO${}_2$) of 20 bar for La${}_4$Ni${}_3$O${}_{10}$ and 140 bar for Pr${}_4$Ni${}_3$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${}_4$Ni${}_3$O${}_{10}$ (R=La, 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 post-growth rapid cooling. Both La${}_4$Ni${}_3$O${}_{10}$ and Pr${}_4$Ni${}_3$O${}_{10}$ crystals undergo a metal-to-metal transition (MMT) below room temperature. In the case of Pr${}_4$Ni${}_3$O${}_{10}$, the MMT is found at ~157.6 K. For La${}_4$Ni${}_3$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, demonstrates a not insignificant coupling between electronic and lattice degrees of freedom in these trilayer nickelates.

21 pages, 8 figures, 3 tables