Synthesis and characterization of infinite-layer La_1-xCa_xNiO₂ single crystals

Superconductivity was recently discovered in Sr-doped RNiO₂ (R = Pr, Nd) thin films. However, first experiments on polycrystalline powder samples reveal no superconducting transition, raising the question whether epitaxy to a substrate is required for superconductivity in nickelates. So far, high-quality bulk single-crystalline samples have not been investigated, although they might host properties distinct from powders. We have therefore synthesized perovskite nickelate single crystals with various rare-earth cations R and dopant elements using flux growth under high pressure via a Walker-type multi-anvil apparatus. We found that especially the compound La_0.8Ca_0.2NiO₃ can be synthesized with excellent crystalline quality and without traceable impurity phases. We will present the synthesis of La_0.8Ca_0.2NiO₃ and the reduction to La_0.8Ca_0.2NiO₂, together with results from scanning transmission electron microscopy, x-ray diffraction, magnetic susceptibility, electronic transport, and Raman spectroscopy measurements.