On the incorporation of nickel into hexagonal barium titanate: magnetic properties and electron paramagnetic resonance (EPR)

Systematic measurements of the magnetic moment of hexagonal 6H-BaTiO3 + 0.04 BaO + x NiO (0.005 ≤ x ≤ 0.02) ceramics were performed to study the influence of Ni ions on the magnetic properties. By temperature-dependent measurements of the paramagnetic susceptibility at 90 kOe, the Ni2+ ion was identified as the majority defect in air-sintered Ni-doped hexagonal barium titanate. Q-band EPR investigations of a 2.0 mol% Ni-doped single crystal revealed three different Ni centers located at Ti sites: first, Ni3+ ions at Ti sites in intact oxygen octahedra, second, Ni3+ associated with an oxygen vacancy and third, the presence of Ni2+ centers leading to a forbidden transition. The Ni3+—VO associate characterized by a vacancy in the face-sharing oxygen plane of the oxygen octahedra can be ruled out. The crystal field parameters of the Ni2+ defect were estimated by a combined fitting of the paramagnetic susceptibility and the EPR fine structure parameter D to B04\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$B_{0}^{4}$$\end{document} ≈ −17,300 cm−1, B02\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\left| {B_{0}^{2} } \right|$$\end{document} ≈ 2500 cm−1 and B34\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$B_{3}^{4}$$\end{document} ≈ 19,000 cm−1.