16th International Conference on Muon Spin Rotation, Relaxation and Resonance (μSR2025)

Anion Configuration of $A$TaO$_2$N ($A$=Ba, Sr) Studied by μ-LCR

Not scheduled

20m

Poster Presentation Chemistry Poster Session 1

Speaker

Dr Masanori Miyazaki (Muroran Institute of Technology)

Description

In perovskite Ta oxynitrides $A$TaO$_2$N ($A$=Ba, Sr), a new degree of freedom, $cis/trans$, is introduced by the anion configuration. In these materials, a dielectric constant of about 10$^2$-10$^3$ has been observed at room temperature. However, powder X-ray diffractions show structures such as $Pm\bar{3}m$ and ${I4/mcm}$, which have central symmetry and do not exhibit dielectric polarization [1,2]. Powder neutron diffractions also show structures with similar symmetries, although O/N occupancies have been determined. However, the anion configuration has not yet been determined, and two or three candidate crystal structure models have been proposed [3-5]. On the other hand, first-principles DFT calculations suggest that the most stable structure is a tetragonal crystal, rather than a cubic or tetragonal crystal, and among these, the $cis$-type of $Pmc2_1$ is the most stable. Taking into account these results, the $cis$-type of $Pmc2_1$ has been reported to be the most promising candidate [6,7].
This study aims to obtain insight into the O/N configuration from the viewpoint of local structure. Muon cross-resonance ($\mu$-LCR) experiments were performed on powder $A$TaO$_2$N ($A$=Ba, Sr) samples. The experiment was performed at S1-ARTEMIS, J-PARC with a magnetic field dependence at 50 K. The muon sites were estimated from Hartree potential calculations by DFT using the ab-initio calculation package VASP.
In addition, the nuclear quadrupole resonance magnetic field of $^{14}$N nuclei observed through muons was estimated by calculating the charge density distribution and then performing EFG calculations from the charge density distribution. In my talk, I will show the results observed in $\mu$-LCR and discuss the expected structure.

References:
[1] A. Hosono, $et$ $al$., Solid State Sci. 144 (2023) 107310.
[2] S-K. Sun, $et$ $al$., J. Amer. Ceram. Soc. 97 (2014) 1023-1027.
[3] M. Yang, $et$ $al$., Nat. Chem. 3 (2011) 47– 52.
[4] Y-R. Zhang, $et$ $al$., J Ceram. Soc. Jpn. 119 (2011) 581– 586.
[5] K. Page, $et$ $al$., Chem. Mater. 19 (2007) 4037– 4042.
[6] S. H. Porter, $et$ $al$., Cryst. Growth Des. 14 (2014) 117.
[7] Y. Masubuchi, $et$ $al$., Chem. Mater. 36 (2024) 7504– 7513.