共查询到20条相似文献,搜索用时 15 毫秒
1.
The magnetic properties of La0.60R0.07Di0.33MnO3 ferromagnetic manganites (Di = Sr, Ba) are studied, where La is partly replaced by magnetic rare earths R. It is shown that (i) there is a ferromagnetic coupling between Mn and R spins, (ii) the Curie temperature is lowered compared to the parent La compound and (iii) its depression is correlated with the effective moment of the rare earth ion. This last relation is tentatively explained by a magnetic pair-breaking effect, where fluctuating R moments lower the double-exchange coupling between Mn atoms. 相似文献
2.
A. Ecija K. VidalA. Larrañaga A. Martínez-AmestiL. Ortega-San-Martín M.I. Arriortua 《Solid State Ionics》2011,201(1):35-41
Ln0.5M0.5FeO3-δ (Ln = La, Nd, Sm; M = Ba, Sr) perovskites have been synthesised by the glycine-nitrate route in order to obtain compounds with good morphological and electrical characteristics to be used as SOFC cathodes. A systematic study of the influence of the average ionic radius of the A cation (<rA>), on the structural, morphological and electrical properties of these perovskites has been performed. The obtained materials have been characterised by ICP-AES analysis, X-ray powder and neutron powder diffraction, scanning electron microscopy and four-probe conductivity measurements. In this study <rA> has been changed in the range 1.34 ≥ <rA > ≥ 1.25 Å, while keeping constant the doping level, x = 0.5 (in A position) and A cation size disorder, σ2 (rA) = 0.0161 Å2. Overall, the sample with the higher average ionic radius showed the highest values of conductivity. Chemical compatibility of the proposed cathodes with yttria-stabilised zirconia electrolyte (YSZ) has also been analysed. The data indicate that additional phase formations exist in all systems at temperatures above ~ 1000 °C. 相似文献
3.
The charge order (CO) domains of dimensionally controlled manganites Pr1−xCaxMnO3 and Pr1−xCa1+xMnO4 (x=0.5, 0.6 and 0.67), which have three-dimensional (3D) and two-dimensional (2D) Mn-O networks, respectively, have been studied by transmission electron microscopy (TEM). Although the electron diffraction data show similar dependences of the modulation wave vector on hole doping x, there are distinctive differences between the 3D and 2D systems in terms of the CO domain sizes. In the 2D system, the TEM images show that the domain size is almost constant irrespective of hole doping x. On the other hand, in the 3D system, the domain size of the incommensurate CO for x=0.6 is much smaller than those of the commensurate CO for x=0.5 and 0.67. Namely, in the 3D system, the CO states are strongly influenced by the incommensurability for the parent lattice. This difference indicates that the dimension of the Mn-O network plays a crucial role in the CO domain and suggests that the electron-lattice coupling of the 3D system is stronger than that of the 2D system. 相似文献
4.
5.
A.A. Yaremchenko A.V. Kovalevsky E.N. NaumovichV.V. Kharton J.R. Frade 《Solid State Ionics》2011,192(1):252-258
Phase relationships, thermal expansion and electrical properties of Mg1 − xFexO (x = 0.1-0.45) cubic solid solutions and Fe3 − x − yMgxCryO4 ± δ (x = 0.7-0.95; y = 0 or 0.5) spinels were studied at 300-1770 K in the oxygen partial pressure range from 10 Pa to 21 kPa. Increasing iron content enlarges the spinel phase stability domain at reduced oxygen pressures and elevated temperatures. The total conductivity of the spinel ceramics is predominantly n-type electronic and is essentially p(O2)-independent within the stability domain. The computer simulations using molecular dynamics technique confirmed that overall level of ion diffusion remains low even at high temperatures close to the melting point. Temperature dependencies of the total conductivity in air exhibit a complex behavior associated with changing the dominant defect-chemistry mechanism from prevailing formation of the interstitial cations above 1370-1470 K to the generation of cation vacancies at lower temperatures, and with kinetically frozen cation redistribution in spinel lattice below 700-800 K. The average thermal expansion coefficients of the spinel ceramics calculated from dilatometric data in air vary in the range (9.6-10.0) × 10− 6 K− 1 at 300-500 K and (13.2-16.1) × 10− 6 K− 1 at 1050-1370 K. Mg1 − xFexO solid solutions undergo partial decomposition on heating under oxidizing and mildly reducing conditions, resulting in the segregation of spinel phase and conductivity decrease. 相似文献
6.
The phase stability, thermal expansion, electrical conductivity, and oxygen permeation of perovskite-type oxides Ba0.5Sr0.5(Co0.8Fe0.2)1 − xNbxO3 − δ (x = 0 − 0.2) have been investigated. Room-temperature X-ray diffraction of as-prepared powders indicates that in the investigated compositional range solid solutions are formed. Long-term annealing experiments both in flowing air and nitrogen, at 750 °C, demonstrate that the phase instability observed in parent Ba0.5Sr0.5Co0.8Fe0.2O3 − δ (BSCF) is suppressed already at the minimum substitution of 5 mol% of niobium for (Co, Fe). Both electrical conductivity and thermal expansion are found to decrease with increasing niobium concentration, which behaviors can be explained by defect chemical considerations, taking into account charge compensation mechanisms by doping BSCF with Nb5+ donor cations. The oxygen permeation flux of 10 mol% Nb-substituted BSCF, in the range 800-900 °C, is reduced by 10% relative to that found for parent BSCF. Switching from helium to a CO2-containing purge gas results in a severe reduction or cessation of the oxygen flux. Options are discussed to avoid undesired formation of surface carbonates. 相似文献
7.
Yifang Ouyang Xiaoma Tao Hongmei Chen Yuanping Feng 《Physica B: Condensed Matter》2009,404(16):2299-2304
The elastic constants of the Al, Mg and rare earth (RE) lanthanide elements have been calculated at T=0 K by using the projector augmented-wave (PAW) method within the generalized gradient approximation (GGA). The bulk moduli, shear moduli, Young's moduli and Poisson's ratio of poly-crystalline solid are estimated from the calculated elastic constants of single crystal. Based on the quasi-harmonic Debye model, the Debye temperature, heat capacity, Grüneisen parameter and linear thermal expansion coefficient are also estimated. The present calculated results are in reasonable agreement with the available experimental data and other theoretical results. The present calculation of elastic constants for Ce also indicates that the PAW potential (named “Ce_3”), for which one f electron is kept frozen in the core and hence fix the valency of Ce to three (Ce_3) does not yield good results for the elastic constants. 相似文献
8.
S.K. Arora Vipul Patel R.G. Patel Brijesh Amin Anjana Kothari 《Journal of Physics and Chemistry of Solids》2004,65(5):965-973
The a.c. and d.c. conductivity of SrC4H4O6·3H2O are measured and are found to lie between usual conductivities of semiconductor and insulator. Temperature dependence of d.c. conductivity shows intrinsic conduction, which is confirmed by the slope of versus data. Due to application of thermal energy, noticeable conductivity peaks imply liberation of water molecules during dehydration and the formation of strontium oxalate. The conductivity plot has a nature similar to the intrinsic-to-extrinsic transition found in normal semiconductors. There occurs Efros hopping conduction in our samples. 相似文献
9.
Dysprosium metal layers deposited on (100)Si substrates were annealed in situ at 300 °C for different time intervals in order to produce DySi2−x layers at several stages of growth. Electron microscopy work showed that silicon reacts with Dy metal through the simultaneous growth of an amorphous interlayer and a polycrystalline phase to form DySi2−x. Compressive stresses due to volumetric changes during the reaction deform the produced silicide layer and induce roughness at the surface and interface. 相似文献
10.
Effect of co-doping Yb, Gd and Ce in scandia stabilized zirconia (SSZ) on the phase stability, high temperature aging behavior and ionic conductivity was studied. Both binary (10 mol% SSZ) and the ternary (co-doped) compositions were found to be in single cubic phase in the as-processed condition. However, the binary composition exhibited the rhombohedral ‘β’ phase after sintering whereas the ternary compositions remained in the single cubic phase. The sintered pellets were aged at 900 °C for 500 h in air to study the phase stability at high temperature. Transmission electron microscopy revealed that the aged samples of Yb and Gd co-doped compositions contain small amount of the tetragonal phase which resulted in considerable degradation in conductivity (more than 20%). The Ce co-doped sample, on the other hand, was in single cubic phase after aging and this ensured that conductivity reduction was minimal in this composition. The co-doped samples however, showed higher conductivity before and after aging compared to the binary composition. The rhombohedral ‘β’ phase was absent in all the co-doped ternary compositions even after high temperature aging. 相似文献
11.
Apatite silicates have recently been reported as promising electrolyte materials for intermediate temperature solid oxide fuel cells (IT-SOFCs). In this work, a series of apatite-type compounds La9.67Si6-xAlxO26.5-x/2 (LSAO) with x = 0-2 are synthesized by the sol-gel process at calcining temperature of 800-900 °C. Thermal expansion coefficient, relative density and electrical conductivity of these samples with different Al doped contents are investigated. A symmetrical cell, which is composed of La9.67Si5AlO26 electrolyte and (La0.74Bi0.10Sr0.16)MnO3+δ (LBSM) cathode, is fabricated and electrochemically characterized. LBSM cathode shows a good electrochemical performance, which proves LBSM to be a promising candidate cathode for LSAO-based electrolyte. 相似文献
12.
Mahdi S. Lataifeh 《Applied Physics A: Materials Science & Processing》2008,92(3):681-685
The saturation magnetization (M
s) and the initial magnetic susceptibility (χ
in) of substituted yttrium iron garnet (YIG) Ho3−x
Y
x
Fe5O12 where (x=0,0.3,1.5), pure terbium iron garnet Tb3Fe5O12, and substituted aluminum iron garnet (AlIG) Ho3Fe5−x
Al
x
O12 where (x=0.05,0.7) at room temperature are reported. It has been observed that M
s and χ
in decrease in a linear manner as Ho3+ replaces Y3+ in yttrium iron garnet. For substituted (AlIG), a drastic decrease in both M
s and χ
in as Al3+ ions replace Fe3+ ions. The rate of decrease of M
s and χ
in with the increase of Al3+ for substituted (AlIG) is greater than that for substituted (YIG). That is attributed to the decrease in the superexchange
interaction (self and mutual iron interactions) with Al substitution. 相似文献
13.
Nozomu Tsuboi Takanobu Hoshino Tomonori Suzuki Keizo Kato Futao Kaneko 《Journal of Physics and Chemistry of Solids》2005,66(11):2134-2138
Delafossite-type oxides of CuTbyY1−yO2, CuEuyY1−yO2, CuCaxTbyY1−x−yO2 and CuCaxEuyY1−x−yO2 have been prepared by solid state reactions. The lattice-parameter dependence on the composition implies substitution of the Tb3+, Eu3+ and Ca2+ cations for the Y3+ site. Noticeable sharp emission lines due to the f-f transitions (5D4→7FJ, J=3-6) of Tb3+ or due to the f-f transitions (5D0→7FJ, J=0-4) of Eu3+ are observed at room temperature. Electrical conductivities of CuCaxTbyY1−x−yO2 and CuCaxEuyY1−x−yO2 are larger than those of CuTbyY1−yO2 and CuEuyY1−yO2, indicating the increase of the hole concentration caused by the substitution of Ca2+ for the Y3+ site. These results indicate the controllability of the luminescence and conductivity in CuCaxTbyY1−x−yO2 and CuCaxEuyY1−x−yO2 delafossite-type oxides by simultaneous substitution of the rare earth Tb3+ or Eu3+ cation and the Ca2+ cation for the Y3+ site. 相似文献
14.
《Current Applied Physics》2014,14(4):590-595
In this study, we reported the effects of the boron (B) substitution into the Ca site in the Ca3Co4O9 system on the electrical, thermal and magnetic properties between 300 K and 5 K. The results indicated that the B-substitution into the system caused an increase of resistivity due to the decrease on carrier concentration. Thermal conductivity decreased for the x = 0.5 B-substituted sample and then increased with increasing the B-content. Analysis on the thermal conductivity of samples showed that the phonon–phonon interaction term is the dominant component in the total thermal conductivity for all the samples. It was found that the point defect contribution to the thermal conductivity increased by increasing the B-content. The temperature dependence of magnetic susceptibility showed a paramagnetic behavior at room temperature and ferrimagnetic behavior below 20 K for unsubstituted sample. But, the magnetization decreased in the B-substituted samples. The substitution of B into the Ca site destroyed the interlayer coupling, which resulted in the decrease of the ferromagnetic behavior. The susceptibility data was fitted using Curie–Weiss law with temperature independent term and the μeff values were calculated to be 1.42 μB and 3.89 μB for unsubstituted sample and the highest B-substitution, respectively. 相似文献
15.
Manuela Ferrara Heinz-Christoph Neitzert Maria Sarno Giuliana Gorrasi Diana Sannino Vittoria Vittoria Paolo Ciambelli 《Physica E: Low-dimensional Systems and Nanostructures》2007,37(1-2):66
The effect of the electrical field on the conductivity of linear low-density polyethylene/carbon nanotubes/ (LLDPE/CNT) composites during temperature cycling has been investigated. Under applied voltage a positive resistivity temperature coefficient was observed during heating already at low (2–3 wt%) CNT content, followed by a large negative temperature coefficient during cooling whose value depends on the applied voltage. The resistivity values after thermal cycling were markedly lower, while they slightly increased in the absence of an electrical field. The effects of thermal cycling on structural and physical properties of the composites have been evaluated by X-ray diffraction and differential scanning calorimetry. 相似文献
16.
17.
Measurements relating to molar magnetic susceptibility, dc electrical conductivity and thermoelectric power of Nd, Sm, Eu
and Gd are reported. The ac electrical conductivity at a few temperature ranges is also given. It is found that it follows
the Curie-Weiss law behaviour and this has been attributed to the crystal field effect. The experimental value of Bohr magneton
for the magnetic ions has been found to be in good agreement with theory. Thermoelectric power is negative in the measured
temperature range suggesting these materials to bep-type semi-conductors and holes as the dominant charge carriers. The results are explained using band theory. 相似文献
18.
Mohd. Hashim Alimuddin Shalendra Kumar Sagar E. Shirsath E.M. Mohammed Hanshik Chung Ravi Kumar 《Physica B: Condensed Matter》2012,407(21):4097-4103
Manganese zinc ferrites (MZF) have resistivities between 0.01 and 10 Ω m. Making composite materials of ferrites with either natural rubber or plastics will modify the electrical properties of ferrites. The moldability and flexibility of these composites find wide use in industrial and other scientific applications. Mixed ferrites belonging to the series Mn(1−x)ZnxFe2O4 were synthesized for different ‘x’ values in steps of 0.2, and incorporated in natural rubber matrix (RFC). From the dielectric measurements of the ceramic manganese zinc ferrite and rubber ferrite composites, ac conductivity and activation energy were evaluated. A program was developed with the aid of the LabVIEW package to automate the measurements. The ac conductivity of RFC was then correlated with that of the magnetic filler and matrix by a mixture equation which helps to tailor properties of these composites. 相似文献
19.
Shuyan Li Zhe Lü Xiqiang Huang Bo Wei Wenhui Su 《Journal of Physics and Chemistry of Solids》2007,68(9):1707-1712
Crystal structure, thermogravimetry (TG), thermal expansion coefficient (TEC), electrical conductivity and AC impedance of (Ba0.5Sr0.5)1-xLaxCo0.8Fe0.2O3-δ (BSLCF; 0.05?x?0.20) were studied in relation to their potential use as intermediate temperature solid oxide fuel cell (IT-SOFC) cathode. A single cubic pervoskite was observed by X-ray diffraction (XRD). The TEC of BSLCF was increasing slightly with the increasing content of La, and all the compounds showed abnormal expansion at high temperature. Proved by the TG result, it was associated with the loss of lattice oxygen. The electrical conductivity, which is the main defect of Ba0.5Sr0.5 Co0.8Fe0.2O3-δ (BSCF), was improved by La doping, e.g., the compound of x=0.20 demonstrated a conductivity of σ=376 S cm−1 at 392 °C. The increase of electrical conductivity resulted from the increased concentration of charge carrier induced by La doping. In addition, the AC impedance revealed the better electrochemical performance of BSLCF. For example, at 500 °C, the sample with composition x=0.15 yielded the resistance values of 2.12 Ω cm2, which was only 46% of BSCF. 相似文献
20.
The effect of nickel substitution on defect chemistry, electrical properties, and dimensional stability of calcium-doped yttrium chromite was studied for use as an interconnect material in high temperature solid oxide fuel cells (SOFCs). The compositions of Y0.8Ca0.2Cr1 − xNixO3 ± δ (x = 0-0.15), prepared using the glycine nitrate process, showed single phase orthorhombic perovskite structures over a wide range of oxygen partial pressures (4.6 × 10− 20 atm ≤ pO2 ≤ 0.21 atm at 900 °C). X-ray diffraction (XRD) analysis indicated that most of the nickel ions replacing chromium ions are divalent and act as acceptor dopants, leading to a substantial increase in conductivity. In particular, the conductivity at 900 °C in air increased from 10 S/cm to 34 S/cm with 15% nickel substitution, and an increase in charge carrier density was confirmed by Seebeck measurements, which validated the predominant Ni2+ oxidation state. A point defect model was derived, and the relationship between electrical conductivity and oxygen partial pressure was successfully fitted into the proposed model. The defect modeling results indicated that nickel substitution improves the stability of calcium-doped yttrium chromite toward reduction and suppresses the oxygen vacancy formation, which results in significantly increased electrical conductivity in reducing environment. The electrical conductivity of Y0.8Ca0.2Cr0.85Ni0.15O3 ± δ at 900 °C in reducing atmosphere (pO2 = 10− 17 atm) was 5.8 S/cm, which was more than an order of magnitude higher than that of Y0.8Ca0.2CrO3 ± δ (0.2 S/cm). Improved stability in reducing atmosphere was further confirmed by dilatometry measurements showing reduced isothermal “chemical” expansion, and the isothermal expansion in reducing atmosphere (pO2 = 10− 17 atm) at 900 °C decreased from 0.07% for Y0.8Ca0.2CrO3 ± δ to 0.03% for Y0.8Ca0.2Cr0.85Ni0.15O3 ± δ. Based on these results, enhanced electrical performance and mechanical integrity is expected with nickel substitution on calcium-doped yttrium chromite in SOFC operating conditions. 相似文献