0000000000160639
AUTHOR
O. Bidault
Influence of B-site chemical ordering on the dielectric response of the Pb(Sc1/2Nb1/2)O3relaxor
The influence of chemical B-site ordering between Sc3+ and Nb5+ cations on the properties of the Pb(Sc1/2Nb1/2)O3 (PSN) relaxor has been investigated. Depending of the degree of ordering, PSN exhibits different behaviours. For a completely disordered material, a relaxor–ferroelectric phase transition is observed at 379 K by DSC. Ordering between Sc3+ and Nb5+ cations on the B-site of the perovskite structure leads to a non-homogeneous material constituted of two phases: ordered and disordered phases. The phase transition temperature of the ordered phase is confirmed to be lower (346 K) than that of the disordered phase. It appears that the phase transition of the disordered phase is shifted…
Improve the dielectric properties of PrSrNi0.8Mn0.2O4 compounds by longer mechanical milling
Abstract Structural and dielectric properties of PrSrNi 0.8 Mn 0.2 O 4 ceramics elaborated by a rapid method combining mechanical milling and heat treatment were studied for the first time. The raw materials are milled at different times ( t mil = 0, 5, 10, 20 and 30 h) and annealed at 1300 °C for 8 h to produce a revealed PrSrNi 0.8 Mn 0.2 O 4 single phase, exhibiting tetragonal structure with space group I 4/ mmm . This result was confirmed by using the TEM/ED pattern for sample milled at 30 h using the [001] orientation. The corresponding lattice images show a well-ordered compound, indicating the absence of stacking faults and the growth of the crystallites. Giant dielectric response …
Structural, microstructural and dielectric studies in multiferroic LaSrNiO4-δ prepared by mechanical milling method
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…
Study of the spontaneous relaxor to normal ferroelectric phase transition in la-doped lead titanate
Abstract Highly lanthanum doped lead titanate ceramics exhibit relaxor properties and undergo on cooling a subsequent spontaneous macroscopic phase transition. The dielectric response is strongly affected by chemical (copper) doping and is found to become independent of the applied ac field for temperatures lower than the phase transition one.
Dielectric relaxation and polaronic hopping in Mn-substituted LaSrNiO4 nickelates prepared by mechanical milling method
Abstract The structures, microstructures and dielectric properties of LaSrNi1−xMnxO4 (x = 0, 0.1, 0.2, 0.3 and 0.5) ceramics synthetized by mechanical milling followed by heat treatment were studied. One single tetragonal phase was revealed in all compounds. Structural parameters were obtained by Rietveld refinement. The substitution of Ni ions by Mn produces a variation of the lattice parameters but no phase change is observed. The surface morphology and elemental analysis of these samples were respectively investigated by Scanning Electron Microscopy (SEM) and energy dispersive X-ray technique (EDS). Giant dielectric response was observed in these ceramics, and at least two relaxations we…
Space-charge relaxation in perovskites.
We report a dielectric anomaly in several perovskites at intermediate frequencies 10\ensuremath{\le}f\ensuremath{\le}${10}^{7}$ Hz in the temperature range 400 \ifmmode^\circ\else\textdegree\fi{}C \ensuremath{\le}T\ensuremath{\le}800 \ifmmode^\circ\else\textdegree\fi{}C. We have found this dielectric maximum in more than 100 samples of various shapes and textures. This anomaly is shown to arise from a Debye dielectric dispersion that slows down following an Arrhenius law. We have established a link between this dielectric relaxation and the conductivity. We propose that it can be achieved through a space-charge model that quantitatively agrees with the experimental results in the lower temp…
The Ba2LnFeNb4O15 “tetragonal tungsten bronze”: Towards RT composite multiferroics
Several Niobium oxides of formula Ba2LnFeNb4O15 (Ln = La, Pr, Nd, Sm, Eu, Gd) with the Tetragonal Tungsten Bronze (TTB) structure have been synthesised by conventional solid-state methods. The Neodymium, Samarium and Europium compounds are ferroelectric with Curie temperature ranging from 320 to 440K. The Praseodymium and Gadolinium compounds behave as relaxors below 170 and 300 K respectively. The Praseodymium, Neodymium, Samarium, Europium and Gadolinium compounds exhibit magnetic hysteresis loops at room temperature originating from traces of a barium ferrite secondary phase. The presence of both ferroelectric and magnetic hysteresis loops at room temperature allows considering these mat…
Substitution effects on the relaxor properties of lead magnesium niobate ceramics
Abstract The temperature dependence of the dielectric permittivity is studied in different Pb(Mg⅓Nb⅔)O3 based ceramics, in which the ordered region size can be changed by introducing titanium or lanthanum ions. Both the relaxor behaviour and the nonlinear dielectric component are found to be dependent on the impurity content. Especially, the nonlinearity increases strongly as the material exhibits a more conventional ferroelectric behaviour, i.e. as the size of the polar clusters, which develop in the paraelectric matrix, increases.
Enhancement of the dielectric response through Al-substitution in La1.6Sr0.4NiO4 nickelates
The structures and dielectric properties of La1.6Sr0.4Ni1−xAlxO4 (x = 0, 0.2 and 0.4) ceramics elaborated using the Pechini method were studied for the first time. The same unique tetragonal phase was found in all compounds. The lattice parameters were found using Rietveld refinement. The surface morphology characterization and elemental analysis of these samples were respectively carried out using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). A giant dielectric response was observed in these ceramics, and one dielectric relaxation was found. The substitution of nickel with aluminum results in a colossal dielectric constant value (>106). The dielectric l…
Dielectric spectroscopy measurements of the sub-Tg relaxations in amorphous ethyl cellulose: A relaxation magnitude study
Amorphous ethyl cellulose exhibits three secondary relaxations at temperatures below its glass transition. The fitted parameters that describe these processes and the comparison with other polysaccharides allow to ascribe the relaxations to lateral groups on one hand and to local main chain motion on the other hand. Their contributions to the dielectric constant overlap and induce a broad dielectric losses peak. The amplitude of one of these relaxations is found to decrease regularly with time. It is believed it comes from a gradual change of the polar groups chemical environment that constrains their motion.
Normal and relaxor ferroelectric behavior in the Ba1−xPbx(Ti1−yZry)O3 solid solutions
Abstract Polycrystalline samples of Ba 1−x Pb x (Ti 1−y Zr y )O 3 (BPTZ) with x = 0.025 & 0.1 and 0.10 ≤ y ≤ 0.50 have been synthesized by high-temperature solid-state reaction technique. X-ray diffraction reveals the formation of single phase with tetragonal or cubic structure. Dielectric investigations were carried out in the temperature range from 80 to 445 K with frequencies range from 10 2 to 10 6 Hz. A broad dielectric anomaly coupled with the shift of dielectric maxima toward a higher temperature with increasing frequency indicates either a diffuse phase transition or relaxor behavior in some of these ceramics. Whatever lead content, when zirconium is substituted by titanium, T C an…
Polaronic relaxation in perovskites
We report a low-temperature loss anomaly in several oxidic perovskites such as ${\mathrm{KTaO}}_{3}$, ${\mathrm{KTaO}}_{3}$:Nb, ${\mathrm{SrTiO}}_{3}$, ${\mathrm{SrTiO}}_{3}$:Ca, ${\mathrm{PbTiO}}_{3}$:La, Cu, and ${\mathrm{BaTiO}}_{3}$:La. We show that this anomaly arises from a low-frequency dielectric relaxation. The activation energy and the relaxation time of this process are nearly the same for all the investigated perovskites disregarding their composition, texture, and ferroelectric properties. We thus ascribe the loss anomaly to the localization of polarons on residual defects. Although the dielectric losses in ${\mathrm{SrTiO}}_{3}$ and ${\mathrm{SrTiO}}_{3}$:Ca are qualitatively …