共查询到20条相似文献,搜索用时 31 毫秒
1.
Radheshyam Rai Indrani Coondoo Rashmi Rani Igor Bdikin Seema Sharma Andrei L. Kholkin 《Current Applied Physics》2013,13(2):430-440
(1 ? x) K0.5Na0.5NbO3 ? xLiNbO3 (where x = 0.0, 5.0, 5.5, 6.0, and 6.5 wt.%) (KNLN) perovskite structured ferroelectric ceramics were prepared by the solid-state reaction method. X-ray diffraction patterns indicate that single phase was formed for pure KNN while a small amount of second phase (K6Li4Nb10O30, ~3%) was present in LN doped KNN ceramics. Phase analysis indicated the change in the crystal structure from orthorhombic to tetragonal with increase in LN content. The electrical behavior of the ceramics was studied by impedance spectroscopy technique in the high temperature range. Impedance analysis was performed using an equivalent circuit model. The impedance response in pure KNN and KNLN ceramics could be deconvoluted into two contributions, associated with the bulk (grains) and the grain boundaries. Activation energies for conductivity were found to be strongly frequency dependent. The activation energy obtained from dielectric relaxation data was attributed to oxygen vacancies. From PFM we found that the composition with 6.5 wt.% LN displays stronger piezocontrast as compared to pure KNN implying an evidence of a pronounced piezoelectric coefficient. 相似文献
2.
《Current Applied Physics》2015,15(11):1370-1376
Dielectric ceramic materials (1 − x) KNbO3 − xK0.5Bi0.5TiO3 (0 ≤ x ≤ 0.3) have been successfully synthesized via a stirred (dynamic) hydrothermal method. The microstructure, relative density and dielectric properties were studied as a function of KBT doping. The structure of the solid solutions changed from orthorhombic (x = 0; 0.05) to tetragonal (x = 0.1; x = 0.3) at room temperature. The morphotropic phase limit was obtained at x = 0.075 where we have noted the coexistence of the orthorhombic and tetragonal structures. The mean value of the measured dielectric permittivity εr was 700 and dielectric loss tanδ was about 0.06 at room temperature. The dielectric properties of the studied ceramics, from 80 to 450 K, depend not only on their microstructure but also on their relative density. A relaxation behavior was observed for the tanδ curves at temperature below 150 K. The activation energy (Ea) of this phenomenon increases from 0.15 to 0.34 eV with the increase of KBT amount. The conductivity σac remains constant at about 10−6 S m−1. 相似文献
3.
LaxSr1 ? xCoyFe1 ? yO3 ? δ (LSCF) represents one of the state-of-the-art cathode materials for solid oxide fuel cells (SOFCs) due primarily to its high ionic and electronic conductivity. In this study, a one-step infiltration process has been developed to deposit, on the surface of a porous LSCF cathode, a thin film (50–100 nm) of Sm0.5Sr0.5CoO3 ? δ (SSC), which is catalytically more active for oxygen reduction. Electrochemical impedance spectroscopy reveals that the SSC coating has dramatically reduced the polarization resistance of the cathode, achieving area-specific resistances of 0.036 Ω cm2 and 0.688 Ω cm2 at 750 °C and 550 °C, respectively. It has also maintained the stability of LSCF cathodes. In particular, the peak power densities are increased by ~ 22% upon the infiltration of SSC onto the porous LSCF cathodes of our best performing cells. These results demonstrate that a conductive backbone (e.g., LSCF) coated with a catalytic film (e.g., SSC) is an attractive approach to achieving an active and stable SOFC cathode for low-temperature solid oxide fuel cells. 相似文献
4.
《Solid State Ionics》2009,180(40):1683-1689
The complex perovskite (Pr0.75Sr0.25)1 − xCr0.5Mn0.5O3 − δ (PSCM) has been prepared and studied as possible anode material for high-temperature solid oxide fuel cells (SOFCs). PSCM exhibits GdFeO3-type structure and is both physically and chemically compatible with the conventional YSZ electrolyte. The reduction of PSCM resulted in structural change from orthorhombic Pbnm to cubic Pm-3m. Selected area electron diffraction (SAED) analysis on the reduced phases indicated the presence of a √2 × √2 × 2 superlattice. The total conductivity values of ∼ 75% dense Pr0.75Sr0.25Cr0.5Mn0.5O3 − δ at 900 °C in air and 5% H2/Ar are 9.6 and 0.14 S cm− 1 respectively. The conductivity of PSCM drops with decreasing Po2 and is a p-type conductor at all studied Po2. The average TEC of Pr0.75Sr0.25Cr0.5Mn0.5O3 − δ is 9.3 × 10− 6 K− 1, in the temperature range of 100–900 °C and is close to that of YSZ electrolyte. The anode polarization resistance of PSCM in wet 5%H2 is 1.31 Ω cm2 at 910 °C and in wet CH4 at 930 °C; the polarization resistance is 1.29 Ω cm2. PSCM was unstable at 900 °C in unhumidified hydrogen. Cell performance measurements carried out using graded PSCM and La0.8Sr0.2MnO3 as anode and cathode respectively yielded a maximum power density of 0.18 W cm− 2 in wet 5%H2/Ar at 910 °C and the corresponding current density was 0.44 A cm− 2 at 0.4 V. The activation energy for the electrochemical cell operating in wet (3% H2O) 5%H2/Ar fuel is 85 kJ mol− 1. 相似文献
5.
High-temperature compressive creep behaviour of the perovskite-type oxide Ba0.5Sr0.5Co0.8Fe0.2O3 − δ
J.X. Yi H.L. Lein T. Grande S. Yakovlev H.J.M. Bouwmeester 《Solid State Ionics》2009,180(36-39):1564-1568
Compressive creep tests have been performed on perovskite-type Ba0.5Sr0.5Co0.8Fe0.2O3 ? δ ceramics. The activation energy, stress exponent and inverse grain size exponent of the steady-state creep rates are evaluated at p(O2) = 0.21 ? 105 Pa and 0.01 ? 105 Pa in the stress, temperature and grain size ranges 5–20 MPa, 1078–1208 K and 2.5–17.4 µm, respectively. The results indicate that the creep rate of Ba0.5Sr0.5Co0.8Fe0.2O3 ? δ is controlled by diffusion of cations via both the oxide lattice (bulk diffusion) and along grain boundaries. The creep rate of Ba0.5Sr0.5Co0.8Fe0.2O3 ? δ increases profoundly by more than one order of magnitude at 1153–1178 K, which is tentatively linked with the onset of the hexagonal-to-cubic phase transition in this compound. 相似文献
6.
Lan Zhang Xinbing Chen San Ping Jiang Hong Quan He Yan Xiang 《Solid State Ionics》2009,180(17-19):1076-1082
Doped lanthanum manganese chromite based perovskite, La0.7A0.3Cr0.5Mn0.5O3 ? δ (LACM, A = Ca, Sr, Ba), on yttria-stabilized zirconia (YSZ) electrolyte is investigated as potential electrode materials for solid oxide fuel cells (SOFCs). The electrical conductivity and electrochemical activity of LACM depend on the A-site dopant. The best electrochemical activity is obtained on the La0.7Ca0.3Cr0.5Mn0.5O3 ? δ/YSZ (LCCM/YSZ) composite electrodes. The conductivity of LCCM is 29.9 S cm? 1 at 800 °C in air, and the electrode polarization resistance (RE) of the LCCM/YSZ composite cathode for the O2 reduction reaction is 0.5 Ω cm2 at 900 °C. The effect of Gd-doped ceria (GDC) impregnation on the LCCM cathode polarization resistances is also studied. GDC impregnation significantly enhances the electrochemical activity of the LCCM cathode. In the case of the 6.02 mg cm? 2 GDC-impregnated LCCM cathode, RE is 0.4 Ω cm2 at 800 °C, ~ 60 times smaller than 24.4 Ω cm2 measured on a LCCM cathode without the GDC impregnation. Finally the electrochemical activities of the doped lanthanum manganese chromites for the H2 oxidation reaction are also investigated. 相似文献
7.
Monika Karpierz Jan Suchanicz Krzysztof Konieczny Dorota Sitko Pascal Marchet Urszula Lewczuk 《Phase Transitions》2015,88(7):662-667
The 0.5K0.5Bi0.5TiO3–0.5PbTiO3 ceramics were prepared by following a standard solid-state method. The Raman, thermal and dielectric properties of these ceramics were investigated. The X-ray measurements showed that samples have single perovskite-type structure with tetragonal symmetry. Dielectric study revealed that the dielectric behaviour of the investigated ceramics is rather of normal ferroelectrics with large thermal hysteresis. The transition temperature observed by means of differential scanning calorimetry measurements is in good agreement with that obtained from dielectric study. 相似文献
8.
Physics of the Solid State - The structure, dielectric characteristics, and magnetoelectric effect of a 0.5BiFeO3–0.5PbFe0.5Nb0.5O3 multiferroic ceramics are studied. We found that the... 相似文献
9.
Changrong Zhou Xinyu Liu Weizhou Li Changlai Yuan 《Journal of Physics and Chemistry of Solids》2009,70(3-4):541-545
Lead-free piezoelectric ceramics of (1?x?y)Bi0.5Na0.5TiO3–xBi0.5K0.5TiO3–yLiNbO3 (BNT–BKT–LN-x/y) have been fabricated by a conventional solid-state reaction method, and their microstructure and electrical properties have been investigated. The results of X-ray diffraction (XRD) measurement show that K+, Li+ and Nb5+ diffuse into the Bi0.5Na0.5TiO3 lattices to form a solid solution with a pure perovskite structure. The BKT and LN addition has no remarkable effect on the crystal structure. However, a significant change in grain size took place. Simultaneously, with increasing amount of LN, the temperature for a ferroelectric–antiferroelectric phase transition is clearly reduced. The temperature dependence of dielectric properties suggests that the ceramics have diffuse-type phase transition characteristics. The piezoelectric constant d33 and the electromechanical coupling factor kp of the ceramics attain maximum values of 195 pC/N and 0.336 at x=0.18 and y=0.01. 相似文献
10.
11.
A.A. Khurram Nawazish A. Khan M. Mumtaz 《Physica C: Superconductivity and its Applications》2009,469(7-8):279-282
An intercomparison of Fluctuation Induced Conductivity (FIC) of Cu0.5Tl0.5Ba2Can?1CunO2n+4?y (n = 2, 3, 4) [CuTl-12(n ? 1)n] superconductor thin films is given. We tried to find any correlation between the critical temperature and the parameters extracted from the excess conductivity data i.e. cross-over temperature, pseudogap temperature and fluctuation amplitudes. We found that the critical temperature seems to depend on the fluctuation amplitude; greater the fluctuation amplitude higher is the critical temperature. 相似文献
12.
The structure and magnetic properties of Nd0.5Pb0.5-xSrxMnO3 (0≤x≤0.4) manganites were systematically investigated. Significant changes in Curie temperature and metal-insulator (MI) transition temperature of the samples were observed. All samples exhibited a transition from paramagnetic semiconducting to ferromagnetic metallic state.Curie temperature Tc and the MI transition temperature Tp increased with increasing Sr content. We attributed these behaviours to the enhancing of both the double exchange mechanism and the Jahn-Teller electron-phonon coupling. 相似文献
13.
《Current Applied Physics》2010,10(4):1059-1061
Lead-free 0.79(Bi0.5Na0.5)TiO3–0.14[Bi0.5(K0.5−xLix)]TiO3–0.07BaTiO3 (BNBK79 + xLi, x = 0.0, 0.1, 0.2, 0.25, 0.3, and 0.4) ceramics were prepared by conventional solid state reaction process. The crystalline structures and surface morphologies are investigated by X-ray diffraction method and scanning electron microscopy. Dielectric and piezoelectric properties were measured. With increasing of lithium substitution, the Curie temperatures of BNBK79 + xLi ceramics increase, but the maximum value of the dielectric constant decreases. And a relatively large remnant polarization of 17.6 μC/cm2 and 157 pC/N of d33 has been obtained when x = 0.3. 相似文献
14.
Lead-free ferroelectric ceramics with a morphotropic phase boundary (MPB) composition 85.4% (Bi0.5Na0.5)TiO3–2.6%BaTiO3–12.0% (Bi0.5K0.5)TiO3 (BNT-BT-BKT at a molar ratio of 85.4: 2.6: 12.0) doped with 0.8?mol% Nb2O5 were studied for their crystalline phases and microstructure. The crystalline phases were identified using X-ray diffractometry (XRD) with the contents determined using the Rietveld refinement technique. The phase-transformation-induced microstructure was analyzed using transmission electron microscopy (TEM) and the crystal symmetries were determined using the convergent-beam electron diffraction (CBED) technique. Samples sintered at 1200°C contain a mixture of cubic (C-), tetragonal (T-) and rhombohedral (R-) phases at a ratio of C/T/R?=?56.6: 28.4: 15.0?wt%. Two types of grains are produced: one characterized by a featureless contrast consisting of nano-scale T-domains dispersed in a C-phase matrix; the other a core-shell structure with a shell containing twin and anti-phase-boundary (APB) domains coexisting with a (C?+?T)-phase mixture core. The T- and R-twin boundaries are determined to {111}T and {110}R, respectively, and the fault vector for T-APB to R?=?1/2?110]T. The characteristic microstructure is discussed in terms of the reduction in the point group symmetry and changes in the unit cell volume or the Bravais lattice upon phase transformation among the C-, T- and R-phases. The twin and the APB domains are induced and explained. 相似文献
15.
The structure and magnetic properties of Nd_{0.5}Pb_{0.5-x}Sr_xMnO_3 (0≤x≤0.4) manganites were systematically investigated. Significant changes in Curie temperature and metal-insulator (MI) transition temperature of the samples were observed. All samples exhibited a transition from paramagnetic semiconducting to ferromagnetic metallic state. Curie temperature T_C and the MI transition temperature T_p increased with increasing Sr content. We attributed these behaviours to the enhancing of both the double exchange mechanism and the Jahn-Teller electron-phonon coupling. 相似文献
16.
SrTiO3(100) – (√5 × √5) – R26.6 surfaces were studied by means of high-resolution scanning tunneling microscopy (STM) under ultrahigh vacuum conditions. By varying the bias voltage in the occupied state, it was possible to observe the arrangement of titanium and oxygen atoms in the unit cells of a (√5 × √5) surface superstructure, which revealed that the TiO2 layer is the terminating plane of the (√5 × √5) surface. In the STM images, peculiar protrusions were seen at the oxygen fourfold hollow site responsible for √5 × √5 periodicity. The protrusions are asymmetrical in contrast, which would be an important consideration in proposing accurate structural models for (√5 × √5) surface superstructures. 相似文献
17.
Layered LiNi0.5Mn0.5 ? xAlxO2 (x = 0, 0.02, 0.05, 0.08, and 0.1) series cathode materials for lithium-ion batteries were synthesized by a combination technique of co-precipitation and solid-state reaction, and the structural, morphological, and electrochemical properties were examined by XRD, FT-IR, XPS, SEM, CV, EIS, and charge–discharge tests. It is proven that the aliovalent substitution of Al for Mn promoted the formation of LiNi0.5Mn0.5 ? xAlxO2 structures and induced an increase in the average oxidation number of Ni, thereby leading to the shrinkage of the lattice volume. Among the LiNi0.5Mn0.5 ? xAlxO2 materials, the material with x = 0.05 shows the best cyclability and rate ability, with discharge capacities of 219, 169, 155, and 129 mAh g? 1 at 10, 100, 200, and 400 mA g? 1 current density respectively. Cycled under 40 mA g? 1 in 2.8–4.6 V, LiNi0. 5Mn0.45Al0.05O2 shows the highest discharge capacity of about 199 mAh g? 1 for the first cycle, and 179 mAh g? 1 after 40 cycles, with a capacity retention of 90%. EIS analyses of the electrode materials at pristine state and state after first charge to 4.6 V indicate that the observed higher current rate capability of LiNi0. 5Mn0.45Al0.05O2 can be understood due to the better charge transfer kinetics. 相似文献
18.
The europium dopant concentration in strontium cerate was studied to achieve maximum hydrogen permeation. In order to determine high ambipolar conductivity, total conductivity and open circuit potential measurements were performed. Among the three different compositions of Eu-doped SrCe1 ? xEuxO3 ? δ (x = 0.1, 0.15 and 0.2) studied, SrCe0.9Eu0.1O3 ? δ showed highest total conductivity between 600 °C and 900 °C. However, transference number measurements showed increasing electronic conductivity with increasing dopant concentration and a stronger temperature dependence for electronic conduction. Therefore, the highest ambipolar conductivity was obtained over the compositional range from SrCe0.85Eu0.15O3 ? δ to SrCe0.8Eu0.2O3 ? δ depending on temperature. Finally, the hydrogen permeation flux was calculated based on the ambipolar conductivity and compared with experimental results. 相似文献
19.
《Superlattices and Microstructures》1997,21(3):459-461
A series of superconducting cuprates with the nominal composition YBa2Cu3 − xCdxO7 − yand the effect of Cd substitution on Cu sites in this compound is presented. X-ray powder diffraction patterns for these cadmium cuprates with reduced diamagnetism indicate an orthorhombic unit cell like-perovskite structure for (0 ≤ x ≤ 0.15), while for higher Cd concentration, i.e.x = 1.0 the material is polyphasic. The observed superconducting transition temperature of the samples is nearly the same ([formula] K), except for (x = 1.0) whereTcdrops to 72 K and a transition from metallic to semiconducting behavior of the normal state of the resistivity is observed. Such a decrease inTcfor higher Cd concentration could be attributed to the presence of the green phase in this composition. 相似文献