Strain Engineering for Anion Arrangement in Perovskite Oxynitrides

Abstract

Mixed-anion perovskites such as oxynitrides, oxyfluorides, and oxyhydrides have flexibility in their anion arrangements, which potentially enables functional material design based on coordination chemistry. However, difficulty in the control of the anion arrangement has prevented the realization of this concept. In this study, we demonstrate strain engineering of the anion arrangement in epitaxial thin films of the CaSrTaON perovskite oxynitrides. Under compressive epitaxial strain, the axial sites in TaON octahedra tend to be occupied by nitrogen rather than oxygen, which was revealed by N and O K-edge linearly polarized X-ray absorption near-edge structure (LP-XANES) and scanning transmission electron microscopy combined with electron energy loss spectroscopy. Furthermore, detailed analysis of the LP-XANES indicated that the high occupancy of nitrogen at the axial sites is due to the partial formation of a metastable trans-type anion configuration. These results are expected to serve as a guide for the material design of mixed-anion compounds based on their anion arrangements.

Expanding frontiers in materials chemistry and physics with multiple anions

“…d High-pressure reactions. High pressure can prevent some reagents from dissociation or evaporation (upper) 22 – 26 , 41 , and also stabilize dense structures (lower) 27 . e Computational tools.…”

“…XANES is also effective for identifying the above elements and determining their chemical states. Perovskite (Ca 1– x Sr x )TaO 2 N epitaxial films with controlled strains were analyzed using XANES with a polarized light source 41 . From the intensity of π-bonded states of O or N with Ta-5 d via excitation from O and N core levels, it was concluded that N preferably takes the trans configuration in the TaO 4 N 2 octahedron for compressive strain states, which was also supported by STEM-EELS and DFT calculations (Fig.…”

Exploring Metastable Oxynitrides by Thin Film Growth Approach

“…7). To increase the epitaxial strain from substrate, Oka et al synthesized a series of Ca1-xSrxTaO2N films on SrTiO3 substrate and achieved the largest tetragonal strain of c/a ~ 1.05 at x = 0.5 [ 67 ]. Lineally polarized-X-ray absorption near edge structure (LP-XANES) measurements and scanning transmission microscope-electron energy loss spectroscopy of the Ca0.5Sr0.5TaO2N film directly proved that the axial anion sites were predominantly occupied by nitrogen as a result of trans-type N arrangement (Fig.…”

A Partial Anion Disorder in SrVO2H Induced by Biaxial Tensile Strain

“…As mentioned above, the TaO 4 N 2 octahedra in ATaO 2 N are exclusively of cis configuration, but the short-range-ordered state with zigzag -M-N-M-N-chains is not polar (or ferroelectric), which is unfortunate given the more polarizable nature of nitride anions compared with oxide anions. However, the recent thin film study of SrTaO 2 N and its Ca-substituted solid solution has shown that the application of compressive biaxial strain from a SrTiO 3 (STO) substrate induces a partial transformation to trans [12,13], leading to ferroelectric behavior [12].…”

“…The broad FWHM observed in the XRD profiles for the 12h-reacted film (Figure 2a) implies either a certain local variation in anion ordering or buckled [VO 2−x H x ] layers as observed in Ln-doped SrFeO 2+δ [21]. Further studies are necessary to clarify the anion arrangement of this intermediate phase, using, e.g., linearly polarized X-ray absorption spectroscopy as utilized to determine cis/trans-TaO 4 N 2 configuration in Ca-doped SrTaO 2 N [13].…”