Improved control of atomic layering in perovskite-related homologous series

Abstract

Homologous series are layered phases that can have a range of stoichiometries depending on an index n. Examples of perovskite-related homologous series include (ABO3)nAO Ruddlesden–Popper phases and (Bi2O2) (An−1BnO3n+1) Aurivillius phases. It is challenging to precisely control n because other members of the homologous series have similar stoichiometry and a phase with the desired n is degenerate in energy with syntactic intergrowths among similar n values; this challenge is amplified as n increases. To improve the ability to synthesize a targeted phase with precise control of the atomic layering, we apply the x-ray diffraction (XRD) approach developed for superlattices of III–V semiconductors to measure minute deviations from the ideal structure so that they can be quantitatively eradicated in subsequent films. We demonstrate the precision of this approach by improving the growth of known Ruddlesden–Popper phases and ultimately, by synthesizing an unprecedented n = 20 Ruddlesden–Popper phase, (ATiO3)20AO where the A-site occupancy is Ba0.6Sr0.4. We demonstrate the generality of this method by applying it to Aurivillius phases and the Bi2Sr2Can–1CunO2n+4 series of high-temperature superconducting phases.

DyFe2O4: A new trigonal rare-earth ferrite grown by molecular-beam epitaxy

“…3(b), 30 nm thick films of DyFe 2 O 4 could be synthesized with no impurity phases detectable by XRD. Nonetheless, the Bragg peaks of DyFe 2 O 4 in the θ-2θ scan do appear asymmetric, which could indicate the presence of DyFeO 3 intergrowths, 40,41 or this could be caused by other inhomogeneous disruptions to the structure such as variation in oxygenation. As a consequence of the large lattice mismatch between the substrate and film, the film relaxes right away, which is reflected in a large full width at half maximum (FWHM) of 1.36 ○ of the ω rocking curve of the 003 peak of a 30 nm thick film [Fig.…”

Synthesis and electronic properties of Nd$_{n+1}$Ni$_{n}$O$_{3n+1}$ Ruddlesden-Popper nickelate thin films

“…In Sr n+1 Ti n O 3n+1 compounds, deviations from perfect stoichiometry by as much as 5+% often result in imperfect superlattices with rock salt intergrowths or missing rock salt layers but without substantial phase segregation [21,22]. Errors in monolayer dosing times can then be quantitatively estimated and adjusted for purely based on x-ray diffraction spectra of the superlattice phase [23]. The composition, or A:B cation ratio in an ABO 3 compound, can also be perfected using quantitative analysis of the beat frequencies and oscillation lineshapes in the reflection high energy electron diffraction (RHEED) intensities [22,24].…”

“…In other Ruddlesden-Popper systems, areas of locally varying n are frequently observed [23,[41][42][43][44]. To quantify the distribution of the Ruddlesden-Popper layerings, we employ phase lock-in analysis using the (001) pc and (101) pc peaks of the NdNiO 3 perovskite structure [30][31][32].…”

Comparing Thickness and Doping-Induced Effects on the Normal States of Infinite-Layer Electron-Doped Cuprates: Is There Anything to Learn?

“…Advances in oxide thin film deposition processes and, in particular, in oxide molecular beam epitaxy (O-MBE) techniques [ 1 , 2 , 3 , 4 , 5 ] allowing atomic-scale thickness control, abrupt interfaces, and the possibility to change the chemical composition over a distance of a single-unit cell, have given a fundamental burst to the study of the low-dimensional effects in oxide-based heterostructures [ 6 , 7 , 8 , 9 ], allowing the fabrication of these systems with performances comparable to those of the best conventional semi-conductor devices. In particular, several oxide-based quantum-well (QW) systems, where a thin conducting oxide is sandwiched between two layers of insulating oxide material, such as SrTiO 3 /SrVO 3 /SrTiO 3 , GdTiO 3 /SrTiO 3 /GdTiO 3 , SrVO 3 /SrTiO 3 /SrVO 3 , and SmTiO 3 /SrTiO 3 /SmTiO 3 [ 10 , 11 , 12 , 13 , 14 ], have been fabricated and studied.…”