  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 H$_2$ gas or reducing agents
such as CaH$_2$. While the topotactic reduction method has been widely employed
on thin film and polycrystalline powder samples, the reduction of
La$_{1-x}$Ca$_x$NiO$_3$ single-crystals with lateral dimensions up to 150
$\mu$m was achieved only recently, using an indirect contact method with
CaH$_2$. Here we report the topotactic transformation of much larger LaNiO$_3$
crystals with lateral dimensions of more than one millimeter, via direct
contact with CaH$_2$. We characterize the crystalline, magnetic, and electronic
properties of the obtained IL 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 LaNiO$_{2}$ crystals to their powder and thin film
counterparts.
