Using applied pressure to guide materials design: a neutron diffraction study of La2NiO4+δ and Pr2NiO4+δ

Abstract

The compression behaviours of La₂NiO_4+δ and Pr₂NiO_4+δ have been studied up to a pressure of 2.8 and 2.2 GPa respectively. Using neutron diffraction, the mechanism of compression, and the behaviour of the NiO₆ and La/PrO₉ polyhedra in these layered perovskite materials have been determined. Their compression mechanisms have then been compared to related materials (La_2−xPr_xNiO₄, Pr_2−xNd_xNiO₄, La_2−xSr_xNiO₄ and Pr_2−xCa_xNiO₄) where the unit-cell volume has been reduced by controlling the composition (x), which acts as an ‘effective chemical pressure’. Understanding the effects of both has implications for materials design; pressure can be used to finely tune a property, which theoretically may then be emulated using chemical doping.