Crossover between distinct symmetries in solid solutions of rare earth nickelates

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.

Metal–insulator transition in composition-tuned nickel oxide films

“…Extensive previous work has documented an intimate interplay between lattice/structural and electronic properties across the broad family of rare earth nickelates and confirmed in particular the importance of the Ni-O-Ni bond angle [15][16][17][18][19][20][21]. As observed in earlier work [9], the A g -like modes of Nd 1−x La x NiO 3 both soften as the La content is increased, demonstrating that the oxygen octahedral rotations decrease in magnitude. With the reduction of octahedral rotations comes a straightening of the Ni-O-Ni bond angle.…”

“…In addition, LaNiO 3 forms in the R3c symmetry, distinct from the Pnma symmetry of NdNiO 3 , so a composition-driven lattice symmetry transition must occur at a specific value of x that may depend on temperature. This transition has been found to occur at around x = 0.5 at room temperature [9].…”

“…Thus the change in symmetry from Pnma to R3c with increasing x must occur at an x that is larger than x = 0.3. Indeed, previous work found that the room temperature crossover in symmetry from Pnma to R3c with increasing x in the Nd 1−x La x NiO 3 phase diagram occurs at approximately x = 0.5 [9].…”

The impact of Mn nonstoichiometry on the oxygen mass transport properties of La0.8Sr0.2Mn y O3±δ thin films

“…In the central part of the films, the FFT reveals the appearance of additional spots, related with ( 1 /2 1 /2 0) and ( 1 /2 0 0) reflections, as shown respectively in insets 2 and 3 of figure 2(c). These superstructures are characteristic of an orthorhombic structure, originated by antipolar displacement of A-site cations and tilting of the oxygen octahedra (see figure S2 in supporting information for more details) [52,53]. Overall, no structural defects nor secondary phases are visible in the film, confirming the fully epitaxial nature of the layer (see figure S3 in supporting information for more details).…”

Competition between Carrier Injection and Structural Distortions in Electron‐Doped Perovskite Nickelate Thin Films

“…In cases where solid solutions of two materials were deposited by sequential sub-monolayer deposition from two different sputtering targets, the composition of the resulting film was controlled by the precise calibration of the rates of the constituent materials. [79,80] In the study crystalline films of pure PbNiO 3 were not able to be grown to calibrate their growth rate, and therefore a preliminary calibration of the PbNiO 3 growth rate was performed by depositing an amorphous film and measuring its thickness with X-ray reflectivity. The Nd 1−x Pb x NiO 3 www.advelectronicmat.de films were then deposited assuming this growth rate was valid for crystalline films as well, and the precise Pb content of each film was determined after deposition using EDX.…”