authors |
Tkach, A; Almeida, A; Levin, I; Woicik, JC; Vilarinho, PM |
nationality |
International |
journal |
MATERIALS |
author keywords |
electroceramics; perovskites; polar dielectrics; X-ray absorption; Raman spectroscopy |
keywords |
FERROELECTRIC PHASE-TRANSITION; RAMAN-SCATTERING; SPECTROSCOPY; ATHENA; KTAO3; GLASS |
abstract |
Alkaline niobate and tantalate perovskites have attracted attention as polar dielectrics for electronics and telecommunications. Here, we studied the polar behaviour, lattice dynamics, and local structure in conventionally processed K0.985Mn0.015TaO3 +/-delta ceramics using a combination of variable-temperature dielectric and Raman spectroscopies, and X-ray absorption fine structure (XAFS) measurements, respectively. Mn doping induces a low-frequency dielectric relaxation in KTaO3 (KT), which follows the Arrhenius law with an activation energy U approximate to 105 meV and the characteristic relaxation time tau(0) approximate to 4.6 x 10(-14) s. Our XAFS results support preferential Mn occupancy of the cuboctahedral sites as Mn2+, with these cations strongly off-centred in the oversized oxygen cages. Such disordered Mn displacements generate electric dipoles, which are proposed as the source of the observed dielectric relaxation. We show that in Mn-doped ceramics, the low-frequency polar TO1 mode softens on cooling and, at low temperatures, exhibits a higher frequency than in undoped KT. This mode displays no detectable splitting, which contrasts with Li-doped KT that also contains off-centred Li+ species on the cuboctahedral sites. Therefore, we conclude that the coupling between the Mn displacements and the lattice is weaker than in the Li case, and Mn-doped KT therefore exhibits a dielectric relaxation but no ferroelectric transition. |
publisher |
MDPI |
isbn |
1996-1944 |
year published |
2021 |
volume |
14 |
issue |
16 |
digital object identifier (doi) |
10.3390/ma14164632 |
web of science category |
11 |
subject category |
Chemistry, Physical; Materials Science, Multidisciplinary; Metallurgy & Metallurgical Engineering; Physics, Applied; Physics, Condensed Matter |
unique article identifier |
WOS:000689568200001
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ciceco authors
impact metrics
journal analysis (jcr 2019):
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journal impact factor |
3.057 |
5 year journal impact factor |
3.424 |
category normalized journal impact factor percentile |
58.121 |
dimensions (citation analysis):
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altmetrics (social interaction):
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