Site occupancy of Li ions in Li-doped K(Ta_1-xNb_x)O₃ single crystals: reanalysis of inelastic light scattering data and first-principles calculations

Abstract

The Li-doping effects of KTa_1-xNb_xO₃ (KTN) crystals on the site occupancy were investigated by reanalysis of Raman scattering results in the literature and density functional theory (DFT) based first-principles calculations. Above the Curie temperature (T_C), the transformation of the local A₁(z) mode of polar nanoregions (PNRs) of non-doped KTN into the E(x,y) mode of PNRs was reported in 5%Li-doped KTN. The site occupancy for 5%Li-doped-KTN was estimated using DFT results, and it shows that 4.2%Li ions occupy at A-site, while the 0.8%Li ions occupy at B-site. In 5%Li-doped KTN crystals, the hetero-valence random occupation of 0.8%Li ions at B-site can be the microscopic origin of the change of the local mode of PNRs.

KEYWORDS:

• Raman scattering
• polar nanoregions
• random fields
• Li-doped KTN
• density functional theory

Acknowledgments

The one of the authors (M. M. R.) wish to thank to Dr. T. Mori, Dr. M. A. Helal, and Dr. M. Aftabuzzaman for the fruitful discussion and sharing their idea about first-principles calculations.

Additional information

Funding

This study was supported in part by JSPS KAKENHI Grant Number JP17K05030 and a grant (No. 106/5/52/R.U./Eng.) from Faculty of Engineering, University of Rajshahi, Bangladesh.