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Isothermal relaxation of discommensurations in K2ZnCl4
1994
At the incommensurate-ferroelectric transition temperature T c of K 2 ZnCl 4 , the dielectric susceptibility contains an anomalous contribution both above and below T c . Previous quasi-static dielectric measurements and hysteresis loops demonstrated that this anomalous part arises from the peculiar dynamics of discommensurations. We have used isothermal dielectric measurements to get some insight into the long time dynamics of these discommensurations. We have found that the characteristic relaxation times τ are of the order of 10 4 s in the incommensurate and in the ferroelectric phase. Even more unusual is a non-monotonous relaxation which is observed in a restricted temperature range ab…
High temperature oxidation of Mg2(Si-Sn)
2016
Abstract High temperature oxidation of Mg 2 Si 1- x Sn x alloys ( x = 0.1 ⿿ 0.6) has been investigated. The oxidation rate was slow for temperatures below 430 °C. In the temperature range between 430⿿500 °C all the alloys exhibited breakaway oxidation. The onset temperature of the breakaway region in general decreased with increasing level of Sn in the alloy. The breakaway behavior is explained by a combination of the formation of a non-protective MgO layer and the formation of Sn-rich liquid at the interface between the oxide and Mg depleted Mg 2 Sn.
Zn-substituted iron oxide nanoparticles from thermal decomposition and their thermally treated derivatives for magnetic solid-phase extraction
2020
Abstract Controlled thermal decomposition of zinc and iron acetylacetonates in the presence of oleic acid and oleylamine provided surfactant-capped magnetic nanoparticles with narrow size distribution and the mean diameter of ≈15 nm. The combined study by XRD, XRF and Mossbauer spectroscopy revealed three important features of the as-prepared nanoparticles. First, the actual ratio of Zn:Fe was considerably lower in the product compared to the initial ratio of metal precursors (0.14 vs. 0.50). Second, a pure stoichiometric Zn-doped magnetite system, specifically of the composition Zn0.37Fe2.63O4, with no signatures of oxidation to maghemite was formed. Third, Zn2+ ions were distributed at bo…
Properties of Nanosized Ferrite Powders and Sintered Materials Prepared by the Co-Precipitation Technology, Combined with the Spray-Drying Method
2016
Cobalt and nickel ferrites powders are synthesized by the co-precipitation technology, combined with the spray-drying method. The crystallite size, specific surface area (SSA), magnetic properties of synthesized products are investigated. All the synthesized ferrites are nanocrystalline single phase materials with crystallite size of 5-6 nm, the SSA of 80-85 m2/g and the calculated particle size of 13-15 nm. After spray-drying granules of the size up to 10 μm are obtained. After thermal treatment at 550 and 950 °C SSA decreases to 40-50 m2/g and 20-22 m2/g, respectively. The saturation magnetization at these temperatures increase from 17 to 40 emu/g for NiFe2O4 and from 51 to 77 emu/g for C…
Structural, microstructural and dielectric studies in multiferroic LaSrNiO4-δ prepared by mechanical milling method
2016
Abstract The solid solution LaSrNiO 4-δ has been successfully prepared by a rapid method combining mechanical milling and heat treatment. The structure and microstructure transformations were characterized by X-ray powder diffraction, scanning and transmission electron microscopy. The dielectric property was also investigated. After 10 h of milling and 8 h of heat treatment at 1300 °C, X-ray diffraction analysis revealed LaSrNiO 4-δ single phase, exhibiting tetragonal structure with space group of I4/mmm. This result was confirmed by using the ED pattern for sample using the [001] orientation. The corresponding lattice images show the compound to be well ordered, indicating the absence of s…
Oxidation resistance of Ti 3 AlC 2 and Ti 3 Al 0.8 Sn 0.2 C 2 MAX phases: A comparison
2019
Ti3AlC2 and Ti3Al0.8Sn0.2C2 MAX phase powders are densified using Spark Plasma Sintering technique to obtain dense bulk materials. Oxidation tests are then performed over the temperature range 800-1000°C under synthetic air on the two different materials in order to compare their oxidation resistance. It is demonstrated that, in the case of the Ti3Al0.8Sn0.2C2 solid solution, the oxide layers consist in TiO2, Al2O3 and SnO2. The presence of Sn atoms in
Temperature dependence of luminescence of LiF crystals doped with different metal oxides
2020
Photoluminescence and cathodoluminescence of LiF crystals doped with different binary metal oxides were measured in the wide temperature range of 50-300 K and time interval of 10−8−10−1 s after the nanosecond electron excitation pulse. Both as-grown those and crystals irradiated by an electron beam in range of absorbed dose up to 103 Gy were studied. It is shown that spectral-kinetic characteristics of the luminescence depend on the absorbed dose (type of created/accumulated color centers), the irradiation temperature, the concentration of hydroxyl, which promotes incorporation of the MeO complex (Me: W, Ti, Fe, Li) into the crystal lattice, and the cation-dopants.
Antiferromagnetic NiO thickness dependent sign of the spin Hall magnetoresistance in γ-Fe 2 O 3 /NiO/Pt epitaxial stacks
2019
We study the spin Hall magnetoresistance (SMR) in epitaxial γ–Fe2O3/NiO(001)/Pt stacks, as a function of temperature and thickness of the antiferromagnetic insulating NiO layer. Upon increasing the thickness of NiO from 0 nm to 10 nm, we detect a sign change of the SMR in the temperature range between 10 K and 280 K. This temperature dependence of the SMR in our stacks is different compared to that of previously studied yttrium iron garnet/NiO/Pt, as we do not find any peak or sign change as a function of temperature. We explain our data by a combination of spin current reflection from both the NiO/Pt and γ-Fe2O3/NiO interfaces and the thickness-dependent exchange coupling mode between the …
Effect of oxidation post treatments on TiO2 coating manufactured using reactive very low-pressure plasma spraying (R-VLPPS)
2020
Abstract TiO2 coatings manufactured using reactive very low-pressure plasma spraying (R-VLPPS) were analyzed in different regions related to their position compared to the plasma flame. For that, a screen was used in order to hide an area of the substrate from the direct plasma flux. The coating morphology changed from quasi lamellar structure to highly vapor structure and coatings exhibited obvious modifications in terms of phases and mechanical properties. The effect of oxidation post treatment on the as sprayed coating was then studied by selecting two methods: in situ oxidation post treatment and classical thermal treatment. The two post treatments provided an increase of the main rutil…
Raman characterization of Pb2Na1−xLaxNb5−xFexO15 and Pb0.5(5−x)LaxNb5−xFexO15 (0≤x≤1) solid solutions
2011
Abstract The ferroelectric compounds Pb 2 Na 1− x La x Nb 5− x Fe x O 15 and Pb 0.5(5− x ) La x Nb 5− x Fe x O 15 (0≤ x ≤1) with the tungsten bronze type structure have been investigated using Raman spectroscopy. The evolution of the spectra as a function of composition at room temperature is reported. In the frequency range 200–1000 cm −1 three main A 1 phonons around 240 ( υ 1 ), 630 ( υ 2 ) and 816 ( υ 3 ) cm −1 were observed. The broadening of the Raman lines for high values of x originates from a significant structural disorder. This is in good agreement with the relaxor character of these compositions. The lowest-frequency part of the spectra, below 180 cm −1 , reveals a structural ch…