Topotactic transformation of single crystals: From perovskite to infinite-layer nickelates.

Pascal Puphal,Masahiko Isobe,Peter A Van Aken,Y Eren Suyolcu,Hangoo Lee,Matthias Hepting,Mohammad Pakdaman,Jan A N Bruin,Katrin Fürsich,Yu-Mi Wu,Bernhard Keimer,Jürgen Nuss

doi:10.1126/sciadv.abl8091

Pascal Puphal, Masahiko Isobe + Show 10 more

Open Access

https://doi.org/10.1126/sciadv.abl8091

Copy DOI

Abstract

Topotactic transformations between related crystal structures are a powerful emerging route for the synthesis of novel quantum materials. Whereas most such “soft chemistry” experiments have been carried out on polycrystalline powders or thin films, the topotactic modification of single crystals, the gold standard for physical property measurements on quantum materials, has been studied only sparsely. Here, we report the topotactic reduction of La1−xCaxNiO3 single crystals to La1−xCaxNiO2+δ using CaH2 as the reducing agent. The transformation from the three-dimensional perovskite to the quasi–two-dimensional infinite-layer phase was thoroughly characterized by x-ray diffraction, electron microscopy, Raman spectroscopy, magnetometry, and electrical transport measurements. Our work demonstrates that the infinite-layer structure can be realized as a bulk phase in crystals with micrometer-sized single domains. The electronic properties of these specimens resemble those of epitaxial thin films rather than powders with similar compositions.

Highlights

Synthetic routes to materials in which anions are partially removed, inserted, or exchanged are rapidly gaining attention in solid-state physics and chemistry [1,2,3]
For the synthesis of the La1−xCaxNiO3 substitution series, we choose a strongly oxidizing environment using salt flux growth with a perchlorate oxidizer under external pressure from a multi-anvil press implemented in a Walker module (Fig. 1A), which is an established route for the synthesis of RENiO3 crystals [32,33,34]
Tests with several different ampule materials and thicknesses showed that Pt is the most suitable crucible material, it dissolves slowly at the used temperatures (Fig. 1C)

Summary

Introduction

Synthetic routes to materials in which anions are partially removed, inserted, or exchanged are rapidly gaining attention in solid-state physics and chemistry [1,2,3]. The perovskite crystals were reduced to the infinite-layer phase La1−xCaxNiO2+ using CaH2, and the structural, electronic, and magnetic properties were characterized. Local electron energy-loss spectroscopy (EELS) reveals close similarities between the electronic structures of our high-quality infinite-layer crystals and thin films.

Results

Conclusion