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1.
We investigated electrical properties of nanostructured La1?x Sr x FeO3 (0 ?? x ?? 1) from 300 K?C400 K. The nanostructured La1?x Sr x FeO3 (0 ?? x ?? 1) was synthesized by citrate gel method requiring no pH control. X-ray diffraction pattern showed that single phase LaFeO3 with an orthorhombic structure was formed. The structure changed into rhombohedral for x = 0.5 and it became cubic for x = 1.0. For x ?? 0.5, our material showed non-linear current-voltage characteristics and for x > 0.5 it showed linear current-voltage characteristics. Poole Frenkel type conduction mechanism was found to be operative in LaFeO3 from 300 K?C400 K. The experimental values of field-lowering coefficient were by 2.56?C6.41 times higher than the predicted value and were attributed to the presence of localized fields. The increase in conductance with Sr content was due to formation of Fe4+ ions in addition to Fe3+ with the increase in Sr content. Impedance spectroscopy and ac conductivity analysis of La1?x Sr x FeO3 (0 ?? x ?? 1) was also carried out in the temperature range from 300 K?C400 K and frequency was varied from 20 Hz - 2 MHz. The ac conduction followed the correlated barrier hopping model in La0.9Sr0.1FeO3. 相似文献
2.
V. P. S. Awana Anand Pal M. Husain H. Kishan 《Journal of Superconductivity and Novel Magnetism》2011,24(1-2):151-157
We report synthesis, structural details, and magnetization of SmFe1?x Co x AsO with?x ranging from 0.0 to 1.0 at a close interval of 0.10. It is found that Co substitutes fully at the Fe site in SmFeAsO in an iso-structural lattice with a slightly compressed cell. The parent compound exhibited known spin density wave (SDW) character below 150?K. Successive doping of Co at the Fe site suppressed the SDW transition for x=0.05, and later induced superconductivity for x=0.10, 0.15, and 0.20, respectively, at 14, 15.5, and 9?K. The appearance of bulk superconductivity is established by wide open isothermal magnetization M(H) loops. For higher content of Co, i.e. x??0.30, superconductivity is not observed. Clearly, the Co substitution at the Fe site in SmFe1?x Co x AsO diminishes the Fe SDW character (x=0.05), introduces bulk superconductivity for?x from 0.10 to 0.20, and finally becomes a non-superconductor. The SmCoAsO also exhibits a secondary AFM-like transition below or around 50?K. The reported AFM ordering of Sm spins is seen from heat capacity C p(T) at 4.5?K and the same remains invariant with Co doping in SmFe1?x Co x AsO. Further, the FM ordering of Co-spins (seen in magnetization measurements) is not evident in C p(T) studies, suggesting weak correlations between ordered Co-spins in these systems. 相似文献
3.
F. Issaoui M. T. Tlili M. Bejar E. Dhahri E. K. Hlil 《Journal of Superconductivity and Novel Magnetism》2012,25(4):1169-1175
The Ca2?x Sm x MnO4 (x=0?C0.4) compounds were synthesized by a solid?Csolid method and characterized by XRD at room temperature. The XRD profiles were indexed with a tetragonal structure (I/4mmm space group) for x??0.3 and orthorhombic one (Pnma space group) for x=0.4. The magnetic measurements were studied as a function of temperature (T=2?C300?K) and applied field (?? 0 H=0?C10?T). When the temperature decreases, each compound has shown first a ferromagnetic?Cparamagnetic (FM?CPM) transition and then an antiferromagnetic?Cferromagnetic (AFM?CFM) one. The transition temperatures are found to be Sm-doping dependent. For all compounds, a spin-glass phenomenon is evidenced by FC/ZFC magnetization curves. 相似文献
4.
探讨了利用In在真空中予焙烧、生长溶液在乾H_2中焙烧技术以及利用逐次降低生长起始温度的液相外延(LPE)技术生长高纯度的In_(1-X)Ga_XAs(x~0.47)外延片的方法.比较好的电学结果如下:载流子浓度比没经任何焙烧处理低2.5—3个数量级,最好结果为5×10~(15)/cm~3,相应的室温迁移率为8500cm~2/V·S。 相似文献
5.
(BaTiO3)1 ? x (K0.5Bi0.5TiO3) x solid solutions exhibiting positive temperature coefficient of resistance behavior have been prepared using BaTiO3 presynthesized through oxalate coprecipitation. The peak in their dielectric permittivity has been shown to shift to higher temperatures (above 120°C) with increasing x. We have examined the effect of K0.5Bi0.5TiO3 content on the microstructure of the (BaTiO3)1 ? x (K0.5Bi0.5TiO3) x solid solutions. The results demonstrate that, with increasing x, both the minimum and maximum resistivities of the materials in the temperature range of their positive temperature coefficient of resistance behavior increase. The materials prepared using barium titanate presynthesized by the oxalate route have higher Curie temperatures and temperatures where they exhibit positive temperature coefficient of resistance behavior and lower minimum resistivities than do the materials prepared by solid-state reactions. 相似文献
6.
The (Tl0.5Pb0.5)Sr2(Ca1?x Te x )Cu2O7??? (Tl-1212) superconductor for x=0.0 to 0.5 has been prepared and studied by a powder X-ray diffraction method, electrical resistance and AC susceptibility measurements. Most of the samples showed Tl-1212 as the major phase and Tl-1201 as the minor phases. Small amounts of Te substitution (x??0.3) maintained the formation of the Tl-1212 phase but larger amounts led to the formation of 1201 and an unknown impurity phase. The resistance versus temperature curve showed metallic behavior for all samples. The resistance versus temperature curves showed onset transition temperature ( $T_{\mathrm{c\ onset}}$ ) between 92 and 97 K. Our results indicated the combined effects of Te substitution, heating temperature and heating time on the formation and optimization of the (Tl0.5Pb0.5)Sr2(Ca1?x Te x )Cu2O7 superconductor. 相似文献
7.
A. Yu. Mollaev R. K. Arslanov I. K. Kamilov V. M. Novotortsev S. F. Marenkin R. G. Dzhamamedov P. P. Khokhlachev I. V. Fedorchenko 《Inorganic Materials》2012,48(11):1070-1074
The resistivity (??) and Hall coefficient (R H) of n-Cd1 ? x Co x GeAs2 with x = 0.05?C0.15 were measured as functions of temperature (at atmospheric pressure) and pressure (up to p = 7 GPa). The temperature-dependent ?? data were used to determine the ionization energy of a cobalt-related impurity center. In the ??(p) and R H(p) curves, we identified structural semiconductor-semiconductor phase transitions under both increasing and decreasing pressure. Using a mixed-phase structure-effective medium model, we assessed the dynamics of the variation of phase composition with pressure. 相似文献
8.
Gil Drachuck Meni Shay Galina Bazalitsky Rinat Ofer Zaher Salman Alex Amato Christof Niedermayer Dirk Wulferding Peter Lemmens Amit Keren 《Journal of Superconductivity and Novel Magnetism》2012,25(7):2331-2335
We report the successful growth of a large (Ca x La1?x )(Ba1.75?x La0.25+x )Cu3O y (CLBLCO) single crystal. In this material, x controls the maximum of T c ( $T_{c}^{\max }$ ), with minimal structural changes. Therefore, it allows a search for correlations between material properties and $T_{c}^{\max }$ . We demonstrate that the crystals are good enough for neutron scattering and cleave well enough for Raman scattering. These results open new possibilities for cuprate research. 相似文献
9.
Murdochite-type (Mg6–x
Al
x
)MnOm8 (0x0.6) was synthesized at low temperature (700 °C) with the sol-gel process. The specific surface area, crystallite size, catalytic activity for the CO oxidation, and adsorption isotherms of oxygen on (Mg6–x
Al
x
)MnO8 were measured. The increase of the specific surface area with increasing Al3+ ion content was explained by the decrease of the particle size. The catalytic activity increased with increasing Al3+ ion content, and this increase was caused by the valence deviation from the Mn4+ ion to the Mn3.5+ ion. 相似文献
10.
Using first-principles calculation, we study effective electron correlation and spin density fluctuation in iron-based fluorides SrFe1?x Co x AsF (x=0, 0.125). We obtain the observed magnetic moment of Fe atom with a strongly attractive electron correction. Whereas, different from the parent compound, the density of state of superconducting SrFe1?x Co x AsF (x=0.125) near to the Fermi energy is reduced for both signs of effective electron correlation, and suggests strong instability there. In addition, spin density fluctuation resulted from the effective correlation exists in Co-doped compound, may propagate in the form of collective excitation and manifest as spin fluctuation with specific q-vector in momentum space. 相似文献
11.
Masahiko Hiroi Shingo Nakashima Kohei Nakao Tsugumi Rokkaku Masakazu Ito Iduru Shigeta Hirotaka Manaka Norio Terada 《Journal of Superconductivity and Novel Magnetism》2011,24(1-2):753-756
The properties of Heusler compounds Ru2?x Fe x CrGe are investigated and compared with those of Ru1.9Fe0.1CrSi. Ru2CrGe is confirmed to exhibit an antiferromagnetic transition with Ne??l temperature 13?K by magnetic susceptibility and specific heat measurements. When Fe is substituted for Ru, a peak in the magnetic susceptibility is observed, and in the lower temperature region irreversibility between temperature dependences of magnetization for zero-field-cooling and field-cooling conditions is found. Nevertheless, in specific heat of Ru1.9Fe0.1CrGe, there is no anomaly to indicate phase transition. The specific heat is almost identical to that for Ru1.9Fe0.1CrSi. The above results demonstrate that the magnetic states in the low temperature region of Fe-substituted samples are spin-glass-like states. Slight substitution of Fe for Ru destroys the long-range-order and lead to peculiar spin-glass-like states. 相似文献
12.
Rocksalt-type (Ni1–x
Li
x
)O (x=0.1 and 0.2) was synthesized at 1350° C in air and its electrical resistivity (R) was measured under various relative humidities (H). R increases with increasing H in the range 0H79%, reaches a maximum value, then decreases in the range 79%<H100%. The increase in R is explained by an electron boundary layer model. On the other hand, the decrease in R is explained by ionic conductivity. 相似文献
13.
Jwo -Shiun Sun Jon -Jer Yu Jeng -Chei You Chung -Chuang Wei 《Journal of Materials Science》1993,28(8):2163-2168
The dielectric properties of the (1–x)Ba(Zn1/3Nb2/3)O3–xBaSnO3 (0 x 0.32) composition at microwave frequencies were investigated in this study. With the addition of BaSnO3, the dielectric Q(Q
d) value of Ba(Zn1/3Nb2/3)O3 (BZN) can be improved and a small temperature coefficient of resonant frequency (f) can be achieved. When 22.6 mol % of Sn is added to BZN, the characteristics of the Ba(Sn0.226Zn0.258Nb0.516)O3 ceramics sintered at 1500°C are as follows: dielectric constant r = 32, f = + 12 p.p.m.°C1 and high Q
d value of 9700 at 10 GHz. Based on the classical dispersion theory and the logarithmic mixing rule, the effects with additions of substitutional element of BaSnO3 on the microwave dielectric properties of Ba(Zn1/3Nb2/3)O3 can be mostly explained. 相似文献
14.
Dan Xue Hong Zhang Yiyu Li Yulong Liu Zhicheng Li 《Journal of Materials Science: Materials in Electronics》2012,23(7):1306-1312
BaTi1?x Fe x O3?δ (x?=?0.1, 0.2, 0.3) powders were prepared by a wet chemical process polymerized with polyvinyl alcohol, and the related ceramics were obtained by conventional sintering process. The phase component and electrical properties of the ceramics were investigated. The analysis of X-ray diffraction indicates that the BaTi1?x Fe x O3?δ ceramics have a hexagonal crystalline structure. The temperature dependence of resistivity of the ceramics show a characteristic of negative temperature coefficient (NTC) of resistivity with the material constants of around 5,000?K. The impedance analysis reveals that both the grain effect and grain-boundary effect contribute simultaneously to the NTC effect. The conduction mechanisms for the NTC characteristic are proposed to be the electron-hopping model between Fe3+/Fe2+ ions inside grains and the charge carrier transports overcoming the energy barrier of the grain boundary by thermal activation. 相似文献
15.
A. V. Shlyakhtina D. A. Belov S. Yu. Stefanovich O. K. Karyagina L. G. Shcherbakova 《Inorganic Materials》2012,48(11):1126-1130
We have studied terbium substitution for ytterbium in (Yb0.9 ? x Tb x Ca0.1)2Ti2O7 ? ?? (x = 0.1, 0.2, 0.3, 0.4) pyrochlore solid solutions synthesized through coprecipitation followed by firing at 1550°C. The results indicate that only a small amount of terbium (less than 10%) can be incorporated into the pyrochlore structure of (Yb0.9Ca0.1)2Ti2O6.9 because of the large difference in ionic radius between the terbium and ytterbium cations: ??r = r(Tb CN 8 3+ ) ? r(Yb CN 8 3+ ) = 0.055 ?. The oxygen ion conductivity of the (Yb0.9 ? x Tb x Ca0.1)2Ti2O7 ? ?? solid solutions has been determined by impedance spectroscopy in air in the temperature range 300 to 900°C. At high temperatures (t > 640°C), their bulk conductivity was essentially independent of the Yb/Tb ratio. The observed decrease in density and microstructural changes were insignificant. At relatively low temperatures (t < 640°C), the bulk conductivity decreased slightly, and the decrease depended little on terbium concentration. 相似文献
16.
We have studied structure, magnetic and transport properties of polycrystalline samples synthesized with nominal compositions Bi0.2?x Pr x Ca0.8MnO3 (x=0.00, 0.02, 0.04, 0.08, 0.12, 0.16 and 0.20) via a solid-state reaction route. Magnetic measurements show that substitution of Pr at Bi site strongly affect the magnetic and charge-ordering properties. It has been found that the charge-ordering temperature (T CO) decreases with increasing x up to x=0.12 and then after it increases with x up to x=0.20. A spin glass (SG) state has been observed at ??105 K in all the samples. Pr doping also leads to enhancement in the magnetic moment up to x=0.12 and then after a decrease in magnetic moment up to x=0.20. A concomitant increase in resistivity up to x=0.04 and then decrease in resistivity up to x=0.20 is also observed. We propose that the local lattice distortion induced by the size mismatch between the A-site cations and 6s2 character of Bi3+ lone pair electron are responsible for the observed variation in the physical properties with doping content of Pr. 相似文献
17.
A. S. Saidov É. A. Koshchanov A. Sh. Razzakov Sh. K. Ismailov 《Technical Physics Letters》1999,25(12):986-987
Structures comprising Si-Si1−x
Gex-(Ge2)1−x
(InP)x with an intermediate Si1−x
Gex buffer layer were grown on silicon substrates. Morphological examinations, scanning patterns and diffraction spectra, and
also the electrophysical and luminescence properties of the heterostructures were used to show that the crystal perfection
of these structures depends on the choice of liquid-phase epitaxy conditions.
Pis’ma Zh. Tekh. Fiz. 25, 37–40 (December 26, 1999) 相似文献
18.
Perovskite manganites are interesting because of their colossal magnetoresistance. In this work high resolution thermal diffusivity measurements of La1–x
Sr
x
MnO3 (0 x 0.3) single crystals in the temperature range from 250 to 400 K are presented. A photopyroelectric device in the standard back configuration has been used. The thermal diffusivity through second-order magnetic phase transitions, as well as through first- and second-order structural phase transitions has been measured. The critical parameters of the sample with x = 0.3 at the ferromagnetic-to-paramagnetic transition have been obtained, and are close to the values predicted by the Ising model. 相似文献
19.
20.
Dean-Mo Liu 《Journal of Materials Science》1993,28(23):6353-6356
Grain growth in (Ca1–x
,Mg
x
)Zr4(PO4)6 (CMZP) ceramics in the final stage of sintering has been investigated. The grain growth in CMZP ceramics obeys the isothermal grain-growth kinetics with time exponent,n, lying between 1.8 and 2.4 which depends on magnesium content, indicative of a change in grain-growth rate. The time exponent for the grain growth of CMZP can be taken as 2.0 which implies that a normal grain growth develops in the CMZP ceramics. The apparent activation energy for grain growth demonstrates a maximum atx = 0.0 and a minimum atx = 0.1, with 103.2 and 39.4 kcal mol–1, respectively, indicating that a small amount of magnesium promotes grain-boundary migration. The critical grain size for initiating microcracks in the CMZP increases with increasing magnesium and reaches 9–12 m whenx = 0.4. 相似文献