Floating zone growth at high oxygen pressures in Ruddlesden-Popper bilayer nickelate Y$_{y}$Sr$_{3-y}$Ni$_{2-x}$Al$_{x}$O$_{7-\delta}$

Abstract

With the discovery of superconductivity under pressure in the Ruddlesden-Popper (RP) bilayer La$_3$Ni$^{2.5+}_2$O$_7$ and trilayer La$_4$Ni$^{2.66+}_3$O$_{10}$, a new field of nickelate superconductors opened up. In this respect, Sr-Ni-O RP-type phases represent alternative systems that exist with partial cation substitution. We demonstrate that by Y-doping in Sr$_{3}$Ni$_{2-x}$Al$_{x}$O$_7$ (SNAO), as Y$_{y}$Sr$_{3-y}$Ni$_{2-x}$Al$_{x}$O$_7$ (YSNAO), the drawback of an insulating ground state is overcome, and a significant decrease in resistivity is achieved with crystals exhibiting semiconducting behavior. We employ optical floating zone (OFZ) growth at 10 bar oxygen partial pressure to explore the phase formation in a narrow region of Y-Sr-Ni-Al-O and investigate via DFT the general stability of the pure Sr-Ni-O scenario. Using extensive diffraction and spectroscopy, as well as transport and magnetization measurements, the structural, chemical, electrical, and magnetic properties of the as-grown and reduced compounds were investigated. The optimal growth of YSNAO allows for large high quality crystals suitable for neutron studies. In the Al-free growth, a known $n=1$ RP system with Sr$_{1.66}$Y$_{0.33}$NiO$_{4-\delta}$, from which the first single crystals were obtained, was further confirmed, opening the door for future exploration of \textit{A}-site substituted RP-type phases without Ni-site disorder.