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Donor doping of K0.5Na0.5NbO3 ceramics with strontium and its implications to grain size, phase composition and crystal structure
Jitka Hreščak, Goran Dražić, Marco Deluca, Iztok Arčon, Alojz Kodre, M. Dapiaggi, Tadej Rojac, Barbara Malič, Andreja Benčan, 2017, original scientific article

Abstract: In this study, the particular effects of A-site donor doping in a lead-free piezoceramic material K0.5Na0.5NbO3 (KNN) doped with Sr2+, i.e., the crystal-structure change, the secondary-phase formation and the grain-size decrease, were investigated. The already-reported causes of these effects upon doping KNN were critically discussed and a mechanism of the effects’ formation was suggested and experimentally supported with advanced analytical methods. Extended X-ray absorption fine structure (EXAFS) analyses proved that the Sr occupies the perovskite A-sublattice, and locally modifies the KNN monoclinic structure to cubic. With the help of Sr K-edge EXAFS and wavelength-dispersive X-ray spectroscopy, the Sr was found to be homogenously distributed in the KNN perovskite lattice with 0.5, 1 and 2% Sr and no Sr segregation on the nano level was found in any of the studied samples with transmission electron microscopy. Introducing Sr into the A-sublattice, as well as accounting for the charge-compensating A-site vacancies in the starting composition, causes increasing lattice disorder and microstrain, as determined from a Rietveld refinement of the synchrotron X-ray diffraction data. Above 2% Sr the system segregates the A-site vacancies in a secondary phase in order to release the chemical pressure, as revealed by Raman spectroscopy. All these effects result in an increasing number of low-angle grain boundaries that limit the grain growth and finally lead to a significant grain-size decrease.
Found in: ključnih besedah
Summary of found: ...analyses proved that the Sr occupies the perovskite A-sublattice, and locally modifies the KNN monoclinic...
Keywords: perovskite, potassium sodium niobate, donor doping, cation vacancies
Published: 17.01.2017; Views: 2589; Downloads: 209
.pdf Fulltext (2,11 MB)

Unusual magnetodielectric effects in La2CuMnO6 induced by a dynamic crossover in dielectric relaxation at TC
Jasnamol Pezhumkattil Palakkal, Cheriyedath Raj Sankar, Ajeesh Parayancheri Paulose, Matjaž Valant, Artem Badasyan, Manoj Raama Varma, 2018, original scientific article

Abstract: A series of fixed frequency dielectric measurements shows dielectric relaxation in La2CuMnO6, with a dynamic (Arrhenius to Arrhenius) crossover at TC. The external magnetic field alters the relaxation parameters in the vicinity of crossover and induces an unusual trend in the magnetodielectric coupling around TC. A large magnetodielectric coupling of 55% (at 68 K, 4 kHz) and 61% (at 105 K, 285.8 kHz) under a small magnetic field of 5 kOe is discovered. Presence of ferromagnetic short-range correlations above TC and a sign reversal of magnetoresistance around TC are observed. Specific heat analysis revealed the presence of ferromagnetic, variable range hopping active charge localized state. The presence of ferromagnetic short-range correlations and the influence of a core-grain dominated magnetoresistance on the Maxwell-Wagner interfacial polarization are responsible for the observed large magnetodielectric effect. Both the magnetic ordering and external magnetic field control the electric dipole relaxation in the material.
Found in: ključnih besedah
Summary of found: ...Double perovskite Griffiths-like phase Dielectric Magnetoresistance Magnetodielectric...
Keywords: Double perovskite Griffiths-like phase Dielectric Magnetoresistance Magnetodielectric
Published: 03.01.2018; Views: 1746; Downloads: 0
.pdf Fulltext (1,24 MB)

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