Funct. Mater. 2021; 28 (3): 427-436.

doi:https://doi.org/10.15407/fm28.03.427

Dielectric and magnetic properties of KTaO3 co-doped with Li and Co: size effects

S.V.Lemishko1, O.O.Andriiko2, M.M.Prokopiv3, M.O.Tripachko4, I.S.Golovina1,5

1V.Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine, 41 Nauky Ave., 03028 Kyiv, Ukraine
2National Technical University of Ukraine, "Igor Sikorsky Kyiv Polytechnic Institute", 37 Peremogy Ave., 03056 Kyiv,Ukraine
3V.Bakul Institute for Superhard Materials, National Academy of Sciences of Ukraine, 2 Avtozavodska Str., 04074 Kyiv, Ukraine
4Institute of Physics, National Academy of Sciences of Ukraine, 46 Nauky Ave., 03020 Kyiv,Ukraine
5Drexel University, 3141 Chestnut Str., Philadelphia, 19104 PA, USA

Abstract: 

We present dielectric and magnetic properties of potassium tantalate KTaO3 co-doped with Li (4 mol.%) and Co(4 mol. %) for different powder particle sizes: 200 nm (submicron crystals) and 80 nm (nanosized crystals). As-synthesized submicron crystals have a cubic shape with rounded corners, while nanosized crystals have an elongated parallelepiped shape with clear even edges. The dielectric relaxation parameters of Li atoms are determined using the Vogel-Fulcher law: activation energy Ea = 0.0167 eV and characteristic frequency ν0 = 107 Hz. A significant decrease in these parameters was found in comparison with KTaO3 doped only with lithium, which indicates the role of cobalt in the dynamics of off-center lithium atoms. The kinetic parameters describing the relaxation behavior of Co atoms are also determined. The parameters are found to be very close: Ea = 0.387&plusm;0.05 eV, ν0 = (2.5&plusm;0.8)·1013 Hz and Ea =0.391&plusm;0.05 eV, ν0 = (3&plusm;1)·1013 Hz for a submicron and nanosized sample,respectively. The formation of cluster magnetism with the presence of clusters of different sizes is established. As the temperature changes from 110 to 290 K,the average size of clusters increases from 2115 to 3360 and from 3071 to 5577 Co atoms per cluster for a submicron and nanosized sample, respectively.

Keywords: 
potassium tantalate, size effect, relaxor ferroelectric, dielectric relaxation, cluster magnetism.

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