Broadband dielectric response and grain-size effect in K0.5Na0.5NbO3 ceramics
2010 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 107, no 1, 14111- p.Article in journal (Refereed) Published
Dielectric spectra of two K0.5Na0.5NbO3 ceramics with different grain sizes (10 and 0.5 mu m) were measured from 10(2) to 10(14) Hz in a broad temperature range. The sequence of first-order phase transitions (cubic-tetragonal-orthorhombic-rhombohedral) was detected by differential scanning calorimetry, dielectric spectroscopy, and time-domain terahertz spectroscopy. The grain size affects all the phase transitions, which are more smeared in the small-grain sample. In the large-grain ceramics, two well-separated near-Debye relaxations are seen in the tetragonal phase, which suddenly merge on cooling across the tetragonal-orthorhombic transition, and on further cooling the lower-frequency relaxation strongly broadens. On reducing the grain size, the higher-frequency relaxation shifts from similar to 1 to similar to 20 GHz and the lower-frequency one strongly broadens. Without quantitative understanding, these effects could be assigned to domain-wall dynamics and its temperature and grain-size dependences. Similar to pure KNbO3, an overlapped central-mode-soft-mode type excitation was detected in the terahertz range related to the effective hopping and oscillations of the off-centered Nb ions in a multiwell potential.
Place, publisher, year, edition, pages
2010. Vol. 107, no 1, 14111- p.
ceramics, cooling, differential scanning calorimetry, electric strength, grain size, high-frequency effects, potassium compounds, sodium compounds, solid-state phase transformations, submillimetre wave spectra, terahertz wave spectra
IdentifiersURN: urn:nbn:se:su:diva-50316DOI: 10.1063/1.3273490ISI: 000273689600074OAI: oai:DiVA.org:su-50316DiVA: diva2:380744
authorCount :102010-12-222010-12-222010-12-22Bibliographically approved