Synthesis and physical properties of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>LaNiO</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math> crystals
Pascal Puphal, Björn Wehinger, J. Nuss, Kathrin Küster, Ulrich Starke, Gastón Garbarino, B. Keimer, Masahiko Isobe, Matthias Hepting
Abstract
Infinite-layer (IL) nickelates are an emerging family of superconductors whose similarities and differences to cuprate superconductors are under intense debate. To date, the IL phase of nickelates can only be reached via topotactic oxygen reduction of the perovskite phase, using ${\mathrm{H}}_{2}$ gas or reducing agents such as ${\mathrm{CaH}}_{2}$. While the topotactic reduction method has been widely employed on thin film and polycrystalline powder samples, the reduction of ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{NiO}}_{3}$ single crystals with lateral dimensions up to 150 $\ensuremath{\mu}\mathrm{m}$ was achieved only recently, using an indirect contact method with ${\mathrm{CaH}}_{2}$. Here we report the topotactic transformation of much larger ${\mathrm{LaNiO}}_{3}$ crystals with lateral dimensions of more than one millimeter, via direct contact with ${\mathrm{CaH}}_{2}$. We characterize the crystalline, magnetic, and electronic properties of the obtained IL ${\mathrm{LaNiO}}_{2}$ crystals by powder and single-crystal x-ray diffraction (XRD), magnetometry, electrical transport, and x-ray photoelectron spectroscopy (XPS) measurements. The amount of incorporated topotactic hydrogen due to the reduction process is determined by a gas extraction method. In addition, we investigate the evolution of the lattice parameters under hydrostatic pressure up to 12 GPa, using high-resolution synchrotron XRD. Furthermore, we provide a direct comparison of several physical properties of the ${\mathrm{LaNiO}}_{2}$ crystals to their powder and thin film counterparts.