Spinel-structured Ni-free Zn0.9Cu x Mn2.1-x O4 (0.1 ≤ x ≤ 0.5) thermistors of negative temperature coefficient

Most spinel-structured materials of negative temperature coefficient (NTC) contain Ni, which have high cost. In this work, Ni-free Zn_0.9Cu _x Mn_2.1-x O₄ (0.1?≤?x?≤?0.5) NTC material system is developed. X-ray diffraction (XRD) spectra show that Zn_0.9Cu _x Mn_2.1-x O_\intered at 1100 °C crystallizes in a tetrahedral spinel structure, which is caused by the Jahn-Teller effect of the Mn³⁺ ions at the B sites. Cu2p_3/2 X-ray photoelectron spectra (XPS) demonstrate that most of Cu ions located at B sites are at the valance of 2+. The resistivity of Zn_0.9Cu _x Mn_2.1-x O₄ varies from 1,340 Ω cm to 51,489 Ω cm, and B value from 3,357 K to 4,276 K. The resistivity drift after annealing at 150 °C in air for 1,000 h is less than 3 % which is stable enough for practical application.     

Effect of Eu-doping on the magnetic and magnetoresistive properties of La0.65Ca0.35MnO3

The effects of Eu-doping in the A-site on the magnetic and magnetoresistive properties of La_0.65-xEu_xCa_0.35MnO₃ (x = 0, 0.05, 0.10, 0.15) bulk samples have been investigated. All samples have a single perovskite structure. The Curie temperature T _C decreases with increasing Eu content from 268 K for x = 0 to 141 K for x = 0.15. The magnetoresistivity increases with increasing Eu content. Upon an application of a magnetic field of 2.0 T the maximum magnetoresistivity of 97.3% for the La_0.50Eu_0.15Sr_0.35MnO₃ was obtained. It provides an effective way to obtain the high magnetoresistance in the polycrystalline manganites.     

The effects of LSM coating on 444 stainless steel as SOFC interconnect

The effect of oxide (La_0.9Sr_0.1MnO₃, LSM) coating on the commercial stainless steel (STS444) interconnect as SOFC interconnect was examined by measuring the polarization resistance (R _p) of LSCF (La_0.6Sr_0.4Co_0.2Fe_0.8) cathodes of various electrolyte-supported cells (La_0.9Sr_0.1Ga_0.8Mg_0.2 [LSGM], Ce_0.9Gd_0.1O₂ [GDC10], or 8 mol% Y₂O₃-doped ZrO₂ [8YSZ]). The electrochemical impedance of LSCF cathodes was monitored during ～140 h in air at 600 and 700°C to determine the cathodic R _p values. With or without interconnect contacts, the magnitude of cathodic R _p value of LSGM electrolyte was similar to that of GDC electrolyte and much smaller than that of YSZ electrolyte. However, no apparent difference in the rate of increase was observed among the cathodes on the different electrolytes. Although the R _p value of the LSCF cathode in contact with LSM-coated STS444 was much reduced from that with uncoated STS444, the coating was not perfect to prevent the Cr evaporation from the interconnect and thus to avoid the degradation of LSCF cathode. Thus new coating methods or materials are needed to protect the LSCF cathode from the Cr poisoning.     

Performance of La0.9Sr0.1Ga0.5Ni0.5O3 as a Cathode for a Lanthanum Gallate Fuel Cell

The cathodic overpotential of a La_0.9Sr_0.1Ga_0.5Ni_0.5O₃ (LSGN) electrode on a La_0.9Sr_0.1Ga_0.8Mg_0.2O₃ (LSGM) electrolyte was studied using the current interruption technique. The electrode performance was found to be clearly superior to La_0.85Sr_0.15MnO₃ and comparable to La_0.6Sr_0.4CoO₃ in the temperature range of 700–850°C. The exchange current density is a maximum in air and is smaller in either 100% O₂ or 2% O₂ suggesting that the occupation of surface adsorption sites is important. The overpotential-current density curves suggest that charge transfer is the limiting process for high current densities. An energy dispersive spectrometry line scan did not show any significant interdiffusion of Ni ions across the electrode/electrolyte boundary.     

Photoluminescence and ESR identification of γ-ray irradiation induced defects responsible for thermoluminescence in Tb<Superscript>3+</Superscript> activated hibonite (CaAl<Subscript>12</Subscript>O<Subscript>19</Subscript>) powder material

In this paper, we report the effect of Pb doping on the magnetic and magnetocaloric properties of La_0.7Ca_0.3-x Pb _x MnO₃ (0.15?≤?x?≤?0.3) polycrystalline samples. The samples were prepared by solid state synthesis method. X-ray diffraction patterns indicate that these samples have monoclinic structure with the Pc/2 space group. The magnetization measurements indicated that all samples exhibited a paramagnetic–ferromagnetic transition and the transition temperature increased with increasing of Pb concentration. Using phenomenological model, the magnetocaloric behavior of all the samples has been calculated based on the experimental magnetization data. Our results on the magnetocaloric properties suggest that the compound La_0.7Ca_0.15Pb_0.15MnO₃ is attractive as a possible material for magnetic refrigeration.     

High dielectric permittivity of SrBi2Nb2O9(SBN) added Bi2O3 and La2O3

In this paper, the structural and dielectric properties of SrBi₂Nb₂O₉ (SBN) as a function of Bi₂O₃ or La₂O₃ addition level in the radio (RF) and microwave frequencies were investigated. The SBN, were prepared by using a new procedure in the solid-state reaction method with the addition of 3; 5; 10 and 15 wt.% of Bi₂O₃ or La₂O_3. A single orthorhombic phase was formed after calcination at 900 °C for 2 h. The analysis by x-ray diffraction (XRD) using the Rietveld refinement confirmed the formation of single-phase compound with a crystal structure (a?=?5.5129 Å, b?=?5.5183 Å and c?=?25.0819 Å; α?=?β?=?γ?=?90°). Scanning Electron Microscope (SEM) micrograph of the material shows globular morphologies (nearly spherical) of grains throughout the surface of the samples. The Curie temperature found for the undoped sample was about 400 °C, with additions of Bi³⁺, the temperature decreases and with additions of La³⁺ the Curie temperature increased significantly above 450 °C. In the measurements of the dielectric properties of SBN at room temperature, one observe that at 10 MHz the highest values of permittivity was observed for SBN5LaP (5%La₂O₃) with values of 116,71 and the lower loss (0.0057) was obtained for SBN15LaP (15%La₂O₃). In the microwave frequency region, Bi₂O₃ added samples have shown higher dielectric permittivity than La₂O₃ added samples, we highlight the SBN15BiG (15 % Bi₂O₃) with the highest dielectric permittivity of 70.32 (3.4 GHz). The dielectric permittivity values are in the range of 28–71 and dielectric losses are of the order of 10^?2. The samples were investigated for possible applications in RF and microwave components.     

Sintering behavioral and electrochemical performances of LSM-BSB composite cathode for IT-SOFCs

In this paper, La_0.8Sr_0.2MnO₃-Ba_0.1Bi_0.9O_1.5-?? (LSM-BSB) composite cathode was prepared and characterized for intermediate temperature solid oxide fuel cells (IT-SOFCs). XRD results show that no reaction occurred between LSM and BSB at 900°C. SEM results show that the LSM-BSB composite cathode formed good contact with YSZ electrolyte after sintered at 900°C for 2 h, which significantly reduced the sintering temperature of cathode. Compared with the LSM-YSZ electrode sintered at 1200°C for 2 h, LSM-BSB electrode exhibits better electrochemical performance. At 800°C, the area specific resistance (ASR) of the LSM-BSB30 electrode is about 0.168 ??cm², which is nearly 1.5 times lower than that of LSM-YSZ composite cathode.     

Composition-dependent dielectric properties and energy storage performance of (Pb,La)(Zr,Sn,Ti)O3 antiferroelectric ceramics

In this work, Pb_0.97La_0.02(Zr _x Sn_0.95?x Ti_0.05)O₃ (PLZST) (0.5?<?x?<?0.9) tetragonal antiferroelectric (AFE_T) and orthogonal antiferroelectric (AFE_O) ceramics were successfully fabricated by screen printing process. The ceramic materials were in thick-film form bonded with a small amount of glass. The electric field up to 400 kV/cm was presented for antiferroelectric ceramics. Besides, in order to reduce the energy loss of ceramics, the effects of Sn content and temperature on the dielectric properties and energy storage performance of AFE ceramics were investigated. With the increase of Sn content, the forward threshold electric field (E _AF) and backward threshold field (E _FA) decreased and the energy storage density increased obviously. The maximum energy storage density of 5.6 J/cm³ (30 °C) and 4.7 J/cm³ (120 °C) with corresponding energy efficiency of 67 % and 73 % were obtained in Pb_0.97La_0.02(Zr_0.5Sn_0.45Ti_0.05)O₃ ceramic, which makes this material a promising potential application in capacitors for pulsed power systems.     

Improvement of a GDC-based composite cathode for intermediate-temperature solid oxide fuel cells

La_0.84Sr_0.16MnO_3?δ - Ce_0.8Gd_0.2O_2-δ (LSM-GDC) composite cathodes were fabricated by impregnating the LSM matrix with both LSM′ (La_0.84Sr_0.16MnO_3?δ) and GDC (or only GDC), and the ion-impregnated LSM-GDC composite cathodes showed excellent performance. At 750 °C, the value of the cathode polarization resistance (R _p ) was only 0.058 Ω cm² for an ion-impregnated LSM-GDC composite cathode which was impregnated with both LSM′ and GDC. For the performance of the single cell with the same cathode, the maximum power density was 1.1 W cm^?2 at 750 °C. The long-term test of the cell was carried out at 700 °C with a constant load of 0.3 A cm^?2 and the output voltage was stable on the whole. The results demonstrated that LSM-GDC fabricated by impregnating the LSM matrix with both LSM′ and GDC was a promising composite cathode material for the intermediate-temperature solid oxide fuel cells.     

The effect of Co addition on the electrical conductivity of Sr- and Mg-doped LaAlO3

Co was added to see its effect on the electrical conductivity of Sr- and Mg-doped LaAlO₃ (La_0.9Sr_0.1 Al_0.9Mg_0.1O₃, LSAM). Electrical conductivities of La_0.9Sr_0.1(Al_0.9Mg_0.1)_{1− x}Co_xO₃ (LSAMC) for x = 0–0.20 were measured using 2-probe a.c. and 4-probe d.c. method at temperature between 300 and 1300^∘C in air, and as a function of Po ₂ (1–10⁻¹⁵ atm) at 1200^∘C. Electrical conductivities in air increased with increasing Co content, while their activation energy decreased. From the impedance spectroscopy analysis, it was found that both the grain and the grain boundary conductivities of LSAMC samples increased rapidly with Co-addition. LSAMC samples were oxygen ion conductors in low Po₂ and mixed conductors in high Po ₂ up to x = 0.1 just like LSAM. With Co-doping, p-type conductivities increased, however, ionic conductivities remained nearly constant.     

A combination method for improving electrical property of Calcium bismuth niobate ceramics

Calcium bismuth niobate CaBi₂Nb₂O₉ (CBN) ceramic is a promising candidate for high-temperature piezoelectric applications due to its high Curie temperature. However, the extremely low piezoelectric properties hinder its application. A combination method with element doping and texturing was used to improve the electric properties of CBN ceramic. First of all, the Mn element was chosen to be doped to improve the piezoelectric and resistance properties of CBN ceramic. Then, an optimal composition was subsequently textured by templated grain growth (TGG) method to further improve the piezoelectric properties. The piezoelectric properties, Curie temperature (Tc), and resistivity of textured Ca_0.95Mn_0.05Bi₂Nb₂O₉ ceramics (d ₃₃?=?21, k _p?=?10.9 %, Tc?=?942 °C, ρ?=?2.1?×?10⁵Ω·cm at 600 °C) were improved obviously compared to pure random CBN ceramics (d ₃₃?=?6, k _p?=?4.6 %, Tc?=?930 °C, ρ?=?0.6?×?10⁵Ω?·?cm at 600 °C). Furthermore, it has excellent resistance to thermal depoling and keep about 5.7 % kp until the temperature up to 600 °C. This combination method makes the textured Ca_0.95Mn_0.05Bi₂Nb₂O₉ ceramics to be a promising candidate for high-temperature piezoelectric applications.     

Effects of Ni doping on B-site ordering and magnetic behaviors of double perovskite Sr2FeMoO6

Sr₂FeMoO₆ of double perovskite structure has attracted much attention recently, owing to its substantial low-field magnetoresistance reported at room temperature. In our study, a mechanical activation process is devised for successful formation of Ni-doped double perovskite Sr₂(Fe_{1 − x} Ni _x )MoO₆ (0.00 ≤ x ≤ 0.20). For the first time, a single phase of double perovskite is synthesized in air by using MoO₂ as the starting material. Ni doping in Sr₂FeMoO₆ significantly affects its long-range B-site ordering and magnetic behaviors, where the B-site long-range order parameter is progressively enhanced with increasing Ni doping level. Both magnetization and the Curie temperature in Sr₂FeMoO₆ are enhanced significantly by Ni doping, where they both depend almost linearly on the degree of B-site long-range ordering.     

Structure and dielectric properties of Cu and (K,Na) doped SrBi2Nb2O9 ferroelectric ceramics

Ferroelectric ceramics, SrBi₂Nb₂O₉ (SBN), Sr_0.8Cu_0.2Bi₂Nb₂O₉ (SCBN) and Sr_0.8K_0.1Na_0.1Bi₂Nb₂O₉ (SKNBN) were prepared by a solid state reaction process. X-ray diffraction analysis shows that the alkali and Cu almost diffuse into the SBN lattice to form a solid solution during sintering and some slight secondary phases was detected. The effect of alkali and Cu on dielectric properties of the SBN ceramics was discussed. The dielectric loss factor of (K,Na) doped SBN ceramics degraded considerably to 0.01 and their frequency and temperature stabilities were enhanced. The dielectric constant was enhanced by approximately 60% and the Curie temperature (Tc) was also improved for Cu doped SrBi₂Nb₂O₉ ceramics.     

Dielectric and ferroelectric properties of Nb-doped Ba0.8Sr0.2TiO3 ceramics

Ferroelectric and dielectric properties were investigated for Ba_0.8Sr_0.2Ti_(1?5/4x)Nb _x O₃ ceramics with different Nb₂O₅ concentrations. The relations between the ceramic structures and those properties were discussed. The Ba_0.8Sr_0.2TiO₃ doping with 0.01mol% Nb₂O₅ appears to have a strong ferroelectric effect and better dielectric properties. The max permittivity (? _max) is up to 7,521.3 and Ba_0.8Sr_0.2Ti_(1?5/4x)Nb _x O₃ ceramics has higher permittivity even at room temperature. The permittivity presents broadened curves at large temperature ranges, which suggests a non Curie–Weiss behavior near the transition temperature. The diffuse phase transition coefficient (δ) for Ba_0.8Sr_0.2Ti_(1?5/4x)Nb _x O₃ doping with 0.01mol% Nb₂O₅ reaches 0.098, and its P–E loop expresses a diffusing curve. The remanent polarization (2P _r) and coercive field are 31.3 μC/cm² and 10 kV/cm, respectively. The P–E loop presents a diffusing curve, which is relative to the relaxor characteristic.     

Characterization in a Wide Frequency Range (40 MHz–67 GHz) of a KTa0.65Nb0.35O3 Thin Film for Tunable Applications

A (100) oriented KTa_0.65Nb_0.35O₃ 400 nm-thin film has been deposited by Pulsed Laser Deposition on MgO substrate. Microwave measurements, performed on InterDigitated Capacitors, show a paraelectric phase at room temperature with a tunability for the devices of 64% under an electric field of 400 kV/cm. Then, using a specific de-embedding method, the complex permittivity of the KTN thin film has been extracted from 40 MHz up to 67 GHz on coplanar waveguides. As promising applications are pointed out at 60 GHz, such as indoor communications, material characterizations are expected in this spectrum.     

Room temperature multiferroic properties of Mn doped La2Ti2O7

Polycrystalline La₂Ti_2-xMn_xO₇ (LTMO) (x?=?0?0.16) ceramics fabricated by the conventional solid-state reaction are utilized to investigate the effect of Mn doping on the ferroelectric (FE) and ferromagnetism (FM) systematically. Both the FE and FM properties strongly depend on the doping level of Mn atoms, which directly induces a structural phase transition from monoclinic to orthorhombic. Compared with pure La₂Ti₂O₇ (LTO), remnant polarization decreases sharply with the doping level at first, and slightly increases when x?≥?0.08, which is proposed to result from the evolution oxygen vacancies. All the doped samples exhibit weak FM property at room temperature, until the maximum can be observed for x?=?0.08. Mn³⁺-Mn⁴⁺ double-exchange and anti-FM Mn³⁺-Mn³⁺ and Mn⁴⁺-Mn⁴⁺ super-exchange interactions are responsible for the different ferromagnetic behavior of LTMO.     

Effect of Mg doping on dielectric properties of sol-gel derived (Pb0.7Sr0.3)Mg x Ti1–x O3–x thin film

(Pb_0.7Sr_0.3)Mg _x Ti_1–x O_3–x (x?=?0?～?0.3) thin films were successfully prepared on ITO/glass substrate by sol-gel technique. The crystalline phase structures were measured through X-ray diffraction (XRD). The dielectric properties were measured by a precision impedance analyzer. Results show that the perovskite phase was stable in (Pb_0.7Sr_0.3)Mg _x Ti_1–x O_3–x thin film. Its lattice constant was found to decrease with the increase of x when x?<?0.1 and increase when x?>?0.1.The crystalline phase formation and the dielectric properties of the (Pb_0.7Sr_0.3)Mg _x Ti_1–x O_3–x thin film depend on Mg doping content. The phase formation ability was decreased below x?=?0.1 and then increased above x?=?0.1 with the increase in x. The dielectric constant of the thin film is correspondingly changed. The tunabilities of about 35%?～?63% were obtained at 10 kHz. The highest tunability and the lowest dielectric loss of the thin films appeared at x?=?0.2. The FOM of the thin film with Mg doping of x?=?0.2 is about three times higher than that of x?=?0.1 under applied frequency of 10 kHz.     

Low dielectric dissipation and enhanced tunability of Ba0.6Sr0.4TiO3 thin films by the modified composition and multilayer structure

Ba_0.6Sr_0.4Ti_1+yO₃ (BST, y?=?0.1, 0.15, 0.2, 0.25, 0.3) thin films were fabricated on Pt-coated silicon substrates by modified sol-gel techniques. It was found that the tunability of BST thin films and dissipation factor decreased with the increase of Ti content. The multilayer structure of Ba_0.6Sr_0.4Ti_1+yO₃(200 nm)/Ba_0.6Sr_0.4TiO₃(100 nm)/Ba_0.6Sr_0.4Ti_1+yO₃ (200 nm; y?=?0.1, 0.2, 0.25) was designed to enhance the tunability. Our results indicated that the modified composition and multilayer structure were beneficial to lowering the dielectric dissipation and enhancing the tunability simultaneously. The tunability of 26.7% and dielectric dissipation of 0.013 were achieved for modified BST thin films.     

Investigation of magnetic and ferroelectric properties along with the magnetoelectric coupling behavior for asserting a room temperature bi-phase composite as multiferroics

Various composites of nominal composition (1-x)Ba_0.95Ca_0.05TiO₃?+?xLi_0.1Cu_0.1Co_0.1Zn_0.6Fe_2.1O₄ have been prepared and studied thoroughly. X-ray diffraction and Rietveld refinement confirmed the presence of Ba_0.95Ca_0.05TiO₃ and Li_0.1Cu_0.1Co_0.1Zn_0.6Fe_2.1O₄ phases in the composites. The microstructures have been investigated by field emission scanning electron microscopy. Temperature dependent dielectric constant shows two peaks, one is at 150 °C and another at 270 °C for x?=?0.10 composite which resembles the characteristic ferroelectric and ferromagnetic transition peaks. A gradual progression of ferro-para electric transition towards room temperature is observed with doping. The non-Debye type dipole relaxations have been found. The linearity in the log(σ_AC) vs. log(ω) plots indicate that conduction is due to small polaron hopping. The real part of initial permeability increases with growing ferrite concentration but the cut-off frequency decreases. The magnetic property is also enhanced with doping content. The typical ferroelectric hysteresis loops have also seen with the addition of Li_0.1Cu_0.1Co_0.1Zn_0.6Fe_2.1O₄ up to x?=?0.40. The impedance values are found to decreases in the Nyquist plots. The magnetoelectric voltage coefficient is obtained 287?×?10³ V/mT for x?=?0.15 at room temprrature. We found both ferromagnetic and ferroelectric hysteresis loops at room temperature. So, it confirms that the composites exhibit room temperature multiferroicity. This type of composites offers variety of opportunity for multifunctional devices application like hetero-structured read / write memory devices, switching devices and magnetic field sensing devices.

     

Glassy ferromagnetism in La0.75Sr0.25-xKxCoO3 polycrystalline perovskite cobaltites

In this paper, the structural and magnetic properties of La_0.75Sr_0.25-xK_xCoO₃ (0≤x≤0.15) powder samples are reported. X-ray diffraction analysis using Rietveld refinement show that all our samples crystallize in the rhombohedral structure with \( R\overline{3}c \) space group. At low temperatures, with increasing K amount, the samples change from ferromagnetic like behavior (x?=?0, 0.05 and 0.1) to spin glass one (x?=?0.15). The ferromagnetic-paramagnetic transition temperature decreases with increasing K amount from 235K (x?=?0) to 200K (x?=?0.1). In the paramagnetic phase, all our synthesized samples obey the Curie-Weiss law. In the vicinity of T_C, the magnetic entropy change |ΔS _M | for La_0.75Sr_0.2K_0.05CoO₃ sample reached maximum values of 0.47Jkg/K and 2.27Jkg/K under magnetic field variation in the range 1T and 7T, respectively. The magnetization hysteresis loops demonstrate a weakening the ferromagnetism with increasing K content.