Floating zone growth of large tetragonal Ruddlesden-Popper bilayer nickelate YySr3−yNi2−xAlxO7−δ single crystals

Abstract The discovery of superconductivity under high pressure in Ruddlesden-Popper (RP) type phase bilayer {{{La}}}₃{{{Ni}}}₂^2. 5+{{{O}}}₇ La 3 Ni 2 2. 5 + O 7 and trilayer {{{La}}}₄{{{Ni}}}₃^2. 66+{{{O}}}₁₀ La 4 Ni 3 2. 66 + O 10 has initiated the frontier of nickelate-based superconductors. In this context, RP-type phases within the Sr-Ni-O system offer promising alternatives as they offer unconventional high oxidation states and Sr- T -O comprises the usual RP series. Here, the intrinsic stability of the undoped Sr-Ni-O framework is investigated using density functional theory (DFT). While Sr 3 Ni 2 O 7 (SNO) is stable synthesis so far requires Al co-substition in Sr 3 Ni 2− x Al x O 7-δ (SNAO). Y-doping resulting in Y y Sr 3− y Ni 2− x Al x O 7-δ (YSNAO) effectively mitigates the challenge posed by an insulating ground state. This modification yields a substantial reduction in resistivity, with the crystals exhibiting semiconducting behavior. To explore phase formation within the narrow compositional window of the Y-Sr-Ni-Al-O system, single crystals were grown using the optical floating zone (OFZ) technique under an oxygen partial pressure of approximately 10 bar. The optimized growth conditions for YSNAO enabled the production of large (6 × 5 x 3 mm 3), high-quality crystals suitable for neutron scattering experiments. In the absence of Al, crystal growth yielded the n = 1 RP phase Sr 1. 66 Y 0. 33 NiO 4− δ, for which single crystals were obtained. The structural, chemical, electrical, and magnetic properties of both the as-grown and topochemically reduced YSNAO compounds were comprehensively characterized through diffraction, spectroscopy, transport, and magnetization measurements.