On the incorporation of nickel into hexagonal barium titanate: magnetic properties and electron paramagnetic resonance (
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On the incorporation of nickel into hexagonal barium titanate: magnetic properties and electron paramagnetic resonance (EPR) R. Bo¨ttcher1, H. T. Langhammer2,*
1 2
, T. Walther2, S. Ku¨cker2, and S. G. Ebbinghaus2
Fakultät für Physik und Geowissenschaften, Universität Leipzig, Linnéstraße 5, 04103 Leipzig, Germany Institut für Chemie, Martin-Luther-Universität Halle-Wittenberg, Kurt-Mothes-Straße 2, 06120 Halle, Germany
Received: 6 October 2020
ABSTRACT
Accepted: 13 November 2020
Systematic measurements of the magnetic moment of hexagonal 6H-BaTiO3? 0.04 BaO ? x NiO (0.005 B x B 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 B40 & -17,300 cm-1, B20 &
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The Author(s) 2020
2500 cm-1 and B43 & 19,000 cm-1.
Introduction Barium titanate as the prototype of the large perovskite oxide family with ferroelectric and piezoelectric properties is in the focus of solid-state research since decades. Aside from the continuous materials’ investigation for capacitors, actuators and
other passive electronic components, its potential multiferroic properties and the fact that suitably doped BaTiO3 is a dilute magnetic oxide (DMO) [1–4] proves the importance of further research on this material. DMOs or oxide diluted magnetic semiconductors (O-DMS) are promising materials for spintronics and magneto-optics [4–6]. While most of the related investigations used iron as dopant [1–4, 7–9],
Handling Editor: Till Froemling.
Address correspondence to E-mail: [email protected]
https://doi.org/10.1007/s10853-020-05566-7
J Mater Sci
previously also nickel-doped BaTiO3 was studied [9–11]. Barium titanate (BaTiO3) has a variety of phase transitions. Besides the well-known temperaturedriven phase transitions 125 C
0 C
90 C
cubic ! tetragonal ! orthorhombic ! rhombohedral
of the modifications with 3C stacking, this perovskite possesses a hexagonal high-temperature phase with 6H stacking, which can be stabilized down to room temperature via sintering and cooling in reducing atmosphere [12] or by doping with several 3d transition elements [13–15]. The 6H modification of BaTiO3 exhibits its own series of temperature-driven phase transitions [16, 17]: 51 C
199 C
hexagonal ! orthorhombic
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