Abstract
A strong coupling of the lattice to functional properties is observed in many transition metal oxide systems, such as the ABO3 perovskites. In the quest for tailor-made materials, it is essential to be able to control the structural properties of the compound(s) of interest. Here, thin film solid solutions that combine NdNiO3 and LaNiO3, two materials with the perovskite structure but distinct space groups, are analyzed. Raman spectroscopy and scanning transmission electron microscopy are combined in a synergistic approach to fully determine the mechanism of the structural crossover with chemical composition. It is found that the symmetry transition is achieved by phase coexistence in a way that depends on the substrate selected. These results carry implications for analog-tuning of physical properties in future functional materials based on these compounds.
Highlights
Perovskite oxides with the general formula ABO3 comprise a large family of materials owing to the wide variety of cations that can be substituted onto the A- and B-sites
For the x = 0.7 film, only very faint half-order intensity is observed and the fast Fourier transform (FFT) pattern largely corresponds to what would be expected for a purely rhombohedral structure. These results show that for Nd1−xLaxNiO3 on the LaAlO3 substrate, there is a range of compositions where Pnma and R3c symmetries coexist with the higher symmetry rhombohedral phase growing inward from the interface and the surface
The crossover from Pnma is seen to start at around x = 0.5 at room temperature with regions of phase coexistence with both Pnma and R3c symmetries until around x = 0.7, regardless of the sign of the biaxial strain or the substrate symmetry. These observations confirm what was expected for the consideration of these two space groups and show that solid solutions of the type R1−xLaxNiO3 do not represent a continuous tuning in terms of the lattice
Summary
Perovskite oxides with the general formula ABO3 comprise a large family of materials owing to the wide variety of cations that can be substituted onto the A- and B-sites. This high degree of flexibility in chemistry is reflected in the plethora of physical properties that can be obtained ranging from superconductivity to ferroelectricity.. Part of the reason for the chemical flexibility of the perovskite oxide structure stems from the multiple stable ABO3 space groups. A total of 15 space groups can be derived through only cooperative tilts and rotations of the octahedra while maintaining their shape.. A total of 15 space groups can be derived through only cooperative tilts and rotations of the octahedra while maintaining their shape. Cation substitution, polar and antipolar ionic displacements, or Jahn–Teller effects can be accommodated in distorted perovskite structures, giving rise to a great variety of crystal symmetries and corresponding physical properties.
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