Structural and dielectric properties of PrSrNi0.8Mn0.2O4 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 degrees C for 8 h to produce a revealed PrSrNi0.8Mn0.2O4 single phase, exhibiting tetragonal structure with space group I4/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 was observed in these ceramics, and only one dielectric relaxation was found on the curve of a dielectric constant as a function of the temperature. The dielectric loss drops with increasing milling time. For 30 h milling it is divided by 100 at room temperature for low frequencies compared with 5 h milling. An equivalent circuit [R-C][R-CPE] was used to fit the experimental data and provide the activation energy of the thermally activated relaxation. Using the same nominal composition, the milling time has a major effect on the dielectric constant by significantly reducing the losses. (C) 2017 Elsevier B.V. All rights reserved.

Lead-free electroceramics samples of composition Ba1−xEr2x/3(Ti1−yZry)O3 (BETZ) with x = 0.01 and 0.02 and 0.20 ≤ y ≤ 0.35 have been elaborated by solid-state reaction technique. X-ray diffraction at room temperature discloses a single perovskite phase with a cubic symmetry. Dielectric measurements were carried out in the ranges (80–445 K) and (102–106 Hz) of temperature and frequencies respectively. The ceramics exhibited normal and/or relaxor ferroelectric properties then some of them have very interesting dielectric characteristics in the vicinity of room temperature. A wide dielectric anomaly combined to the dielectric maxima shift toward a higher temperature with increasing frequency denotes either a diffuse phase transition or relaxor behavior in some ceramics. For any erbium concentration, when titanium is substituted by zirconium, the temperature of the permittivity maximum TC (Tm) and the maximum permittivity (ε′rmax) decreases while ΔTm(f)= [Tm(106 Hz) − Tm(102 Hz)] and tan δ increase. The diffuse phase transition parameters were calculated from the modified Curie–Weiss law linear fit. Further a relaxor nature was confirmed and endorsed by a good fit to the Vogel–Fülcher relation.

Polycrystalline samples of Ba1-xPbx(Ti1-yZry)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 and epsilon'r(rmax) decreases while Delta T-m(f) = [T-m(10(6) Hz)-T-m(10(2) Hz)] and tgd increase. The diffuse phase transition parameters were estimated from a linear fit of the modified CurieeWeiss law. A good fit to the VogeleFlcher relation further corroborates suchrelaxor nature. (C) 2016 Elsevier B.V. All rights reserved.

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 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 were found on the curve of the temperature dependence of dielectric constant. An equivalent circuit [R-C][R-CPE] was used to fit the experimental data and provide the activation energy of the thermally activated relaxation. The activation energy values confirm the thermally activated small polaronic hopping contribution to the giant dielectric response. (C) 2016 Elsevier B.V. All rights reserved.

The solid solution LaSrNiO4-delta has been successfully prepared by a rapid method combining mechanical milling and heat treatment. The structure and microstructure transformations were characterized by Xray 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 degrees C, X-ray diffraction analysis revealed LaSrNiO4-delta 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 stacking faults and the growth of the crystallites. Dielectric relaxation of charge-ordered LaSrNiO(4-delta)ceramic was investigated in the temperature range 100-450 K. Giant dielectric response was observed in this ceramic, and only one dielectric relaxation was found on the curve of the temperature dependence of dielectric constant. The thermal activated small polaronic hopping between two charge ordering temperatures should contribute to the giant dielectric response in the present ceramics. (C) 2015 Elsevier B.V. All rights reserved.

Lead free piezoelectric KNbO3 (KN) nanoplates were successfully synthesized through reaction between Nb2O5 and KOH at 220 °C and 10 M KOH during 8 h. The influence of stirring hydrothermal process on the morphology was studied. X-ray patterns confirm the formation of a pure compound with a significant increase in lattice parameters relative to the bibliography. FTIR and TG measurements show the presence of hydroxyl groups located at the surface and in the bulk sample. Transmission electron microscopy observation highlights the formation of superimposed plates of KNbO3. The thickness of the plates corresponds to about twenty cells of orthorhombic KN. The measured dielectric constant εr and tangδ are 540 and 0.03, respectively at 1 kHz and room temperature. A relaxation phenomenon of domains walls has been observed below 150 K in the losses curves and between 450 and 530 K for the permittivity curves.

The BaTi0.4(Fe0.5Nb0.5)0.6O3 ceramic is synthesized by a solid-state reaction technique. The X-ray diffraction of the sample at room temperature shows a cubic phase. The dielectric properties are investigated as a function of frequency (20–106Hz) at different temperatures (80–417K). A giant low frequency dielectric permittivity (εr′∼3.105) was obtained. Two dielectric relaxation peaks were observed on the curve of dielectric loss vs. temperature. The intrinsic dielectric permittivity calculated by impedance spectroscopy from the values of the obtained bulk capacitances were remarkably high 230<εr′<330. The extrinsic factors play an important role on their dielectric response giving rise to a giant dielectric permittivity at T>150K. The heterogeneities conduction in the grains, grain boundaries and interfacial layers are related to a Maxwell–Wagner relaxation.

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 440 K. 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 materials as composites multiferroic. Based on crystal-chemical analysis we propose some relationships between the introduction of Ln3+ ions in the TTB framework and the chemical, structural and physical properties of these materials.

Recently, the concept of polarons has again been at the focus of solid-state research, as it can constitute the basis for understanding the high-temperature superconductivity or the colossal magnetoresistance of materials. More than a decade ago there were some indications that polarons play an important role in explaining low temperature maxima in imaginary part of the dielectric constant ε″(T) in ABO3 perovskites. In the present work we report the ac electrical conductivities of KTaO3; Li and PbTiO3; La, Cu and their frequency and temperature dependence. The real part of the complex ac conductivity was found to follow the universal dielectric response σ′∝νs. A detailed theoretical analysis of the temperature dependence of the parameter s revealed that, at low temperatures, the tunnelling of small polarons is the dominating charge transport mechanism in ABO3 perovskites.

Unpoled and efficient nonlinear optical (NLO) poled sodium niobium borophosphate glasses have been studied by means of dielectric spectroscopy. The thermal poling process induces a dielectric relaxation that gradually vanishes on heating for T≳500K. The data are interpreted by a two-layer (Maxwell-Wagner) model, consisting of a bulk and a Na+ poor surface layer with lower conductivity. Our results suggest that the ion transport is due to hopping mechanism implying at least Na+. All the dielectric results are in full agreement with previous optical analyses. This is an example of poled glasses where an efficient NLO response is directly correlated to the conductivity of the material enhanced by a high alkali loading.

Thin films of Ba(Ti,Zr)O-3 containing about 65% Zr have been grown using rf magnetron sputtering with various substrate temperatures (500-700 degrees C). All of them display ferroelectric relaxor features at low temperature (T < 200 K), namely a frequency dependent maximum of the dielectric permittivity and dispersion on the low temperature side of the peak. This is the first time that such a behaviour has been evidenced in lead-free sputtered thin films.

Pure and well-crystallized Barium Strontium Titanate (BST) nanoparticles with controlled Ba/Sr ratio have been successfully synthesized under supercritical conditions using a continuous-flow reactor in the temperature range of 150-380 degrees C at 26 MPa. To synthesize the Ba0.6Sr0.4TiO3 composition, alkoxides, ethanol and water were used. The resulting nanopowder consists of fine particles with an average particle size of 23 nm. The results show that the Ba/Sr ratio of this powder can be accurately controlled from the composition of precursor. The characterization of the as-synthesized Ba0.6Sr0.4TiO3 solid-solution and the dielectric properties of the sintered ceramics are here reported.

A method based on a seeded growth process was developed to coat ferroelectric nanoparticles with a dielectric silica shell. This method, applied to size-polydispersed (Ba0.6Sr0.4)TiO3 particles (BST, mean diameter 150 nm), allows the control of the silica shell thickness from 2 to 80 nm with an accuracy of 1-2 nm. The morphology and surface physical chemistry of the core-shell were studied by transmission electron microscopy, photon correlation spectroscopy, and zeta potential measurements. A size-sorting procedure consisting of several cycles of centrifugation was optimized to extract the BST@silica nanoparticles of the required size for dielectric properties tuning. Upon sinted ng, dielectric measurements showed that the ferroelectric transition was maintained in the dense nanocomposites.

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.

Lithium thioindate (LiInS$_{2}$) is a new nonlinear chalcogenide biaxial material transparent from 0.4 to 12 $μ$m, that has been successfully grown in large sizes and good optical quality. We report on new physical properties that are relevant for laser and nonlinear optics applications. With respect to AgGaS(e)$_2$ ternary chalcopyrite materials, LiInS$_{2}$ displays a nearly-isotropic thermal expansion behavior, a 5-times larger thermal conductivity associated with high optical damage thresholds, and an extremely low intensity-dependent absorption allowing direct high-power downconversion from the near-IR to the deep mid-IR. Continuous-wave difference-frequency generation (5-11$ μ$m) of Ti:sapphire laser sources is reported for the first time.

Pyroelectric current measurements performed on a LiInS2 monodomain single crystal show a linear variation of the current between 120 and 260K. Near room temperature, a space charge relaxation screens pyroelectricity. The pyroelectric coefficient follows a linear thermal dependence leading to an extrapolated value of 6×10−10CK−1cm−2 at 300K. As for other oxide-type pyroelectric compounds, this value is shown to be proportional to the electro-optic coefficient r333 of LiInS2.