Limits to the strain engineering of layered square-planar nickelate thin films

The layered square-planar nickelates, Nd(n+1)Ni(n)O(2n+2), are an appealing system to tune the electronic properties of square-planar nickelates via dimensionality; indeed, superconductivity was recently observed in Nd(6)Ni(5)O(12) thin films. Here, we investigate the role of epitaxial strain in the competing requirements for the synthesis of the n = 3 Ruddlesden-Popper compound, Nd(4)Ni(3)O(10), and subsequent reduction to the square-planar phase, Nd(4)Ni(3)O(8). We synthesize our highest quality Nd(4)Ni(3)O(10) films under compressive strain on LaAlO(3) (001), while Nd(4)Ni(3)O(10) on NdGaO(3) (110) exhibits tensile strain-induced rock salt faults but retains bulk-like transport properties. A high density of extended defects forms in Nd(4)Ni(3)O(10) on SrTiO(3) (001). Films reduced on LaAlO(3) become insulating and form compressive strain-induced c-axis canting defects, while Nd(4)Ni(3)O(8) films on NdGaO(3) are metallic. This work provides a pathway to the synthesis of Nd(n+1)Ni(n)O(2n+2) thin films and sets limits on the ability to strain engineer these compounds via epitaxy.