La1−xCaxMnO3:Ag0.2 (0.25 ≤ x ≤ 0.31) ceramics with high temperature coefficient of resistivity under magnetic field

The polycrystalline La_1?xCa_xMnO₃ ceramics exhibit good electromagnetic performance, i.e., high temperature coefficient of resistivity (TCR), which can be tuned flexibly with respect to structures. Unfortunately, the magnetic field applied to these materials causes a massive decrease in TCR, which hinders their practical applications. In this study, polycrystalline ceramic La_1?xCa_xMnO₃:Ag_0.2 was fabricated by sol–gel and solid–phase doping methods, and subsequently vast TCR was obtained in the magnetic field for ceramic with x = 0.2. For this polycrystalline material, high value of TCR (58.65%·K^?1, 62.00%·K^?1) could be maintained with or without magnetic field with metal–insulator (M ? I) transition temperature near room temperature range. Extremely high value of TCR in the presence of magnetic field is attributed to the spin–spin coupling effect, which is beneficial to the sensitivity of M ? I transition, generating vast TCR in the magnetic field. Overall, these findings provide new prospects for future applications in infrared bolometers.     

Fabrication and positive temperature coefficient of resistivity properties of semiconducting ceramics based on the BaTiO3–(Bi1/2K1/2)TiO3 system

BaTiO₃–(Bi_1/2K_1/2)TiO₃ (BT–BKT) ceramics have a low ρ_RT of 10¹–10² Ω cm like that of semiconducting materials prepared by sintering in a N₂ flow with low O₂ concentration. By annealing in air, the BT–BKT ceramics show an abrupt increase in their resistivity near the T_c, namely, a positive temperature coefficient of resistivity (PTC) characteristic. With 5 mol% and 10 mol% BKT added to BT, the ceramics display the PTC characteristic at 155 °C and 165 °C, respectively. Furthermore, the ratio, ρ_max/ρ_RT, of the highest resistivity (ρ_max) and the resistivity at room temperature (ρ_RT) of the ceramics increased on adding a small amount of Mn and a sintering aid.     

Structural and magnetic properties of Yb1−xSrxMnO3

The structural and magnetic properties of YbMnO₃ and Yb_0.82Sr_0.18MnO₃ multiferroics were studied by neutron powder diffraction (NPD), magnetometry and electron spin resonance (ESR) technics in a wide temperature range. Neutron diffraction measurements showed that the substitution of ytterbium ions with strontium ions in hexagonal h - YbMnO₃ (space group P6₃cm) leads to the destabilization of the crystal structure of the last compound and appearance of the mixture of three phases with different structure: hexagonal phase h - Yb_0.95Sr_0.05MnO₃ (space group P6₃cm), orthorhombic phase o - Yb_0.69Sr_0.31MnO₃ (space group Pbnm), hexagonal phase SrMnO₃ (space group P6₃cm). This fact was proved by the ESR measurements in which a several signals due to the phases of different structure were observed. NPD measurements showed that the magnetic structure of h - Yb_0.95Sr_0.05MnO₃ phase is similar to the magnetic structure of the pure h - YbMnO₃ and demonstrate the presence of the antiferromagnetic ordering in the samples. ESR and magnetization measurements of h - YbMnO₃ sample proved the presence of the antiferromagnetic correlations and also they showed the appearance of the ferromagnetically correlated nanoregions.     

DC field effect on dielectric property of Ba(ZrxTi1−x)O3 ceramics

Barium zirconate titanate Ba(Zr_xTi_1?x)O₃ (BZT) ceramics have been fabricated by conventional solid state route. The dielectric properties and ferroelectric relaxor behavior were investigated as a function of Zr content and DC bias field. It was found that the relaxor behavior of BZT is enhanced with the increase in Zr content. The temperature of maximum dielectric peak (T_m) of BZT ceramic is greatly increased with DC bias field (E) up to a certain threshold field E_t, below which T_m starts to increase gradually. This behavior could be associated with the size of domain. The relationship between temperature and dielectric tunability is also discussed in details.     

Influence of sintering temperature on energy storage properties of BaTiO3–(Sr1−1.5xBix) TiO3 ceramics

The effect of sintering temperature on microstructure, dielectric properties and energy storage properties of BaTiO₃–(Sr_1?1.5xBi_x)TiO₃ (x = 0.09) (BT–SBT) ceramics was investigated. The sintering temperature has pronounced influence on the grain size, shrinkage, and dielectric properties of the BT–SBT ceramics. With increasing sintering temperature, the dielectric constant increases largely. However, the increasing tendency of the dielectric breakdown strength (BDS) is less noticeable but become more evident with the consideration of Weibull modulus. For the BT-SBT ceramics, the unreleased energy density decreases and the electric field stability of the energy storage efficiency enhances with the increase of sintering temperature.     

Electrical and magnetic properties of La1−xSrxMnO3 (0.1 ≤ x≤ 0.25) ceramics prepared by sol–gel technique

La_1−xSr_xMnO₃ (0.1 ≤ x ≤ 0.25) high density ceramics were prepared by sol-gel method using methanol as solvent. X-ray diffraction analysis showed that all samples exhibited single perovskite structure and no second phase was detected. Scanning electron microscopy images exhibited good particle connectivity on the surface of sample, and grain size increased with the increase in Sr doping. Resistivity-temperature curves of samples were measured by standard four-probe method, and curves exhibited significant differences in studied range of Sr doping. Magnetic measurement results indicated that the variation of susceptibility of different samples was quite different, and the Curie temperature of samples increased with the increase in Sr content. For x = 0.2, temperature coefficient of resistance value of the sample was larger, and corresponding peak TCR temperature was 307.1 K, which is very close to room temperature. Thus, La_0.8Sr_0.2MnO₃ ceramics exhibited high TCR value close to room temperature. Combined with its excellent magnetic properties, La_0.8Sr_0.2MnO₃ ceramics may potentially act as effective candidates for uncooled radiation calorimeter and uncooled magnetic sensor. Applications of La_0.8Sr_0.2MnO₃ ceramics in uncooled infrared radiation calorimeter at room temperature will be highly beneficial.     

Large magnetocaloric effect of La0.67Pb0.33Mn1−xCoxO3 in small magnetic field variation

In this work, we studied in detail the magnetocaloric properties of La_0.67Pb_0.33MnO₃ according to the phenomenological model. Based on this model, a large magnetic entropy change has been discovered in La_0.67Pb_0.33MnO₃ when subjected to low magnetic field variation of 0.05 T. Furthermore, the results of Co doping clearly indicate that the magnetocaloric effect in this system is tunable. Therefore, this tuning makes this ceramic series potentially practical for the improvement of multimaterial layered magnetocaloric regenerators.     

Microstructure and characterization of Ag1−xLixNbO3 ceramics

Silver–lithium niobate, Ag_1−xLi_xNbO₃, is a promising candidate for lead-free piezoelectrics. Ceramic samples for x equal 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.08 and 0.1 were synthesized by solid state reaction. Room temperature X-ray studies indicate that all samples consist mainly of perovskite phase. Only small amounts of secondary phases, namely Ag₂Nb₄O₁₁, Ag and LiNbO₃, appear. For x≈0.06 the orthorhombic–rhombohedral morphotropic phase boundary is observed. Excellent piezoelectric properties, recently reported for x>0.1, may be the result of proximity of morphotropic phase boundary. Scanning electron microscopy and secondary ion mass spectroscopy investigations suggest that the secondary phases occur chiefly at the grain boundaries. Dielectric measurements, carried out in a wide temperature range, revealed that Ag_1−xLi_xNbO₃, for x≤0.05, undergoes the same complex sequence of phase transitions as AgNbO₃. On the other hand, for x>0.06, the temperature dependence of dielectric permittivity exhibits only two maxima, related to transitions from the ferroelectric R phase to the antiferroelectric M phase and followed by the paraelectric O phase. The dielectric results obtained confirm the existence of the morphotropic phase boundary.     

Microstructure effect on dielectric Properties of MgO-doped BaTiO3–BiYO3 ceramics

MgO-doped 0.97BaTiO₃–0.03BiYO₃ (0.97BT–0.03BY) polycrystalline ceramics were prepared by the solid-state sintering method. Then the structural, dielectric and resistant properties were investigated as functions of MgO addition. Microstructure was studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive spectrometry (EDS). The results show that Bi³⁺, Y³⁺ and Mg²⁺ ions exhibit nonuniform distribution behavior in BT–BY ceramics, demonstrating the existence of a “core–shell” structure, which plays important roles in the capacitance-temperature characteristics, where 0.97BT–0.03BY with the addition 2.2–2.8 at% MgO meets the Electronic Industries Association (EIA) X8R (−55 to 150 °C, ΔC/C_25 °C=±15% or less) specification. Moreover, the fine-grained samples with core–shell structure show much higher bulk resistance than the coarse-grained samples over the studied temperature range, which is attributed to the higher proportion of grain boundaries and the lower concentration of the effective acceptor.     

Preparation and ionic conduction of CaZr1−xScxO3−α ceramics

A series of CaZr_1−xSc_xO_3−α (x=0, 0.05, 0.10, 0.15) perovskite oxide ceramics were successfully fabricated at 1400 °C for 10 h and then further sintered at 1650 °C for 10 h via a solid-state reaction sintering process. Conductivities of the ceramics were measured under the atmosphere that contains 1% H₂/Ar and 5.63 kPa H₂O/Ar by the electrochemical impedance spectra technique. It was found that the conductivities of CaZr_1−xSc_xO_3−α (x=0, 0.05, 0.10, 0.15) ceramics increased with the increase of the measuring temperature, and the conductivity achieved its maximum value of 2.03×10⁻⁵–6.5×10⁻³ S cm⁻¹ when the doping amount of Sc (x) was 0.10. Additionally, element doping can increase the conductivities and decrease the conductivity activation energies of CaZr_1−xSc_xO_3−α ceramics. The results of transport number measurement indicated that the CaZr_0.9Sc_0.1O_3−α is almost a pure protonic conductor at 500–750 °C, while it is a mixed protonic-oxygen ionic-electronic conductor at 750–1300 °C.     

Multiscale study of ferroelectric–relaxor crossover in BaSnxTi1−xO3 ceramics

A systematic study of BaSn_xTi_1−xO₃ solid solutions (x = 0–0.20) by a combined field-induced dielectric and ferroelectric analysis with Raman and PFM investigations was realized, in order to obtain new insights concerning the composition-induced modification of the structural phase transitions and ferroelectric–relaxor crossover induced by the increase of Sn addition. The ceramics prepared via solid state reaction and sintering at 1400 °C/4 h showed average tetragonal symmetry for x ≤ 0.15 and cubic for x = 0.20. However, the dielectric and Raman analysis demonstrated that x = 0.05 and x = 0.15 are characterized by a coexistence of phases, which enhances their macroscopic properties (polarization for x = 0.05 and permittivity for x = 0.15). The domain structure shows a gradual modification when increasing Sn addition. No detectable domain structure has been found for x ≥ 0.15. All the compositions show local d₃₃(V) hysteresis loops at room temperature.     

Paradoxical effect of n−3-containing vegetable oils on long-chain n−3 fatty acids in rat heart

Flaxseed, echium, and canola oils contain α-linolenic acid (18∶3n−3, ALA) in a range of concentrations. To examine their effect on elevating cardiac levels of long-chain n−3 FA, diets based on these n−3-containing vegetable oils were fed to rats for 4 wk. Sunflower oil, which contains little ALA, was a comparator. Despite canola oil having the lowest ALA content of the three n−3-containing vegetable oils, it was the most potent for elevating DHA (22∶6n−3) levels in rat hearts and plasma. However, the relative potencies of the dietary oils for elevation of EPA (20∶5n−3) in heart and plasma followed the same rank order as their ALA content, i.e., flaxseed>echium>canola>sunflower oil. This paradox may be explained by lower ALA intake leading to decreased competition for Δ6 desaturase activity between ALA and the 24∶5n−3 FA precursor to DHA formation.     

Experimental and theoretical study on enhanced electrical properties of nickel-substituted La0.5Sr0.5CoO3−δ ceramics

The effect of Ni substitution on the thermal behavior, crystal structure, densification, and electrical properties of La_0.5Sr_0.5Co_1–yNi_yO_3-δ (y = 0.00–0.08) (LSCN) ceramics was discussed based on experimental measurements and theoretical calculations to search for a ruthenium–free and lead–free conductive oxide for thick film resistors. Ceramics were synthesized by the solid–state reaction, and calculations were performed with first–principle density functional theory (DFT). Results showed that the replacement of Ni ion to Co ion could help decrease the densification temperature and enhance the densification level and improve the conductivity of LSCN. Theoretical calculations, including the crystal structure, bond population, total energy, and density of states (DOS), supported the experimental results well. The maximum conductivity of 3155 S/cm was achieved as y = 0.04 was sintered at 1200 °C, and the peak temperature coefficient of resistance (TCR) of 2405.7 ppm/°C occurred at y = 0.06.     

Effect of Zr content on the wetting of BaTi1−xZrxO3 perovskite ceramics by Ag-based liquids

The study of the contact characteristics between functional ceramics and potential electrode metals is of primary importance when developing new devices. BaTiO₃ is the most used dielectric ceramic and its functional properties are tailored by the introduction of substituents. In this work, we verify the effect of the zirconium substituents in BaTi_1?xZr_xO₃ (x = 0, 0.1, 0.2, 0.4) ferroelectric perovskites on the wettability by liquid Ag and Ag-3 at% Cu alloy at 1000 °C in air, and the obtained metal/ceramic interfaces are characterised.With x going from 0 to 0.4, the contact angles increase from 83° to 104° and from 46° to 72° for pure Ag and Ag-3 at% Cu respectively. This trend is in agreement with the increased band-gap energy of the perovskites ascribed to the increase of Zr content. The better wetting of Ag-3 at% Cu compared to pure Ag is due to the formation of interfacial CuO; no further interfacial phenomena nor mutual interdiffusion are detected.     

Effect of SrTiO3 concentration and sintering temperature on microstructure and dielectric constant of Ba1−xSrxTiO3

The Ba_1−xSr_xTiO₃ materials have received increased attention as one of the most important materials for electroceramic components, such as high dielectric ceramic capacitors, tunable phase shifters and PTCR. In this paper, the effect of SrTiO₃ concentration and sintering temperature on the microstructure and dielectric constant of Ba_1−xSr_xTiO₃ materials at the Curie temperature have been investigated. When Ba_1−xSr_xTiO₃ materials were sintered at 1350 °C, the peak value of the dielectric constant, ϵ_max, monotonically decreased with increasing SrTiO₃ concentration. At the sintering temperature of 1400 °C the dielectric constant maximum at the T_C increased with an increase in the x value, reaching the highest value at around x=0.4 and then decreased. As sintering temperature increased to 1450 °C, ϵ_max increased with increasing SrTiO₃ concentration up to x=0.6. The dielectric properties of Ba_1−xSr_xTiO₃ materials were discussed in terms of SrTiO₃ concentration and microstructure.     

Voltage effect of corona poling on characteristics of PbZrxTi1−xO3 (PZT) film

The paper investigates the voltage effect of corona poling on the characteristics of PbZr_xTi_1−xO₃ (PZT) thin film. Purchased PZT powder and lab-made PZT solution were mixed together as sol-gel that was spin-coated on titanium (Ti) substrate. X-ray diffractometer (XRD), scanning electron microscopy (SEM), impedance analyzer were utilized to measure the orientation and dielectric characteristics of films for comparison. The experimental results indicated that the poling voltage would not affect the orientation of crystallization, microstructure and grain size of PZT film surface. However, the higher applied poling voltage would result in better charge storage capacity and energy transfer efficiency of the film.     

Structural and electric properties of polycrystalline Bi1−xErxFeO3 ceramics

Polycrystalline Bi_1?xEr_xFeO₃ ceramics were synthesized by the solid state reaction method followed by rapid liquid phase sintering. The effects of Er substitution on the structure, morphology and electrical properties of the BiFeO₃ multiferroic ceramics were investigated. X-ray diffraction and Raman studies reveal that the structure of BiFeO₃ is changed from rhombohedral to orthorhombic in the Er concentration range of 0.10–0.15, and the impurity phases decrease both due to Er substitution. The X-ray photoelectron spectroscopy shows that Fe²⁺ could be suppressed by Er substitution. The SEM investigations suggest that the Er substitution could significantly reduce the grain sizes and increase the density of the samples. The leakage current is found to be decreased with increasing Er concentration. The dielectric and ferroelectric measurements show that dielectric constant, dielectric loss and ferroelectric properties are strongly dependent on the Er concentration. Er substitution can significantly improve the dielectric constant and remnant polarization, and decrease the dielectric loss by reducing the leakage current.     

Preparation and microwave dielectric properties of Ca0.6La0.8/3(SnxTi1−x)O3 ceramics

Ca_0.6La_0.8/3(Sn_xTi_1−x)O₃ ceramics were prepared via a conventional solid state reaction method, and the effect of Sn doping on their crystal phase structure and microwave dielectric properties was investigated. Results showed that Sn doping could hinder the formation of the rutile TiO₂ detrimental phase of Ca_0.6La_0.8/3TiO₃ ceramic. Also, the Q×f₀ value was enhanced and the τ_f value was lowered by Sn doping. The best microwave dielectric properties, i. e. ε_r=113 and Q×f₀=8487 GHz were obtained for a Sn doping content of 0.02. The mechanism of the improved properties deriving by Sn doping is discussed.     

The influence of doping on flash sintering conditions in SrTi1−xFexO3−δ

Joule heating in flash sintering depends on the sample resistance, which is linked to the charged defects concentration. To study the contribution of defects on the flash sintering mechanism, this link should be untied. In SrTi_1−xFe_xO_3−δ (STFO) system, point defect concentration can be pinned while the resistance is influenced by the oxygen partial pressure (pO₂). SrTi_0.97Fe_0.03O_2.985 onset temperature at different pO₂ was examined at constant oxygen vacancy concentration. The furnace onset temperature decreases with increasing pO₂. The onset temperature of five STFO samples was predicted based on resistance-temperature dependency of the porous green ceramics in a dynamic heat balance simulation. High compatibility of model and experimental results showed reduction of onset temperature with increasing doping. Ex-situ impedance measurements of green samples reveal an overlapping Nyquist plots close to the sample onset temperature. This indicates that the onset is determined by the green body resistance regardless how it has been achieved.