共查询到20条相似文献,搜索用时 15 毫秒
1.
P. Mele C. Artini G.A. Costa R. Masini 《Journal of Physics and Chemistry of Solids》2009,70(2):276-280
Phase relation studies in the Gd2O3-Nd2O3 system have been performed on (Gd1−xNdx)2O3 samples (0?x?1) with the purpose of performing a systematic study of the composition effects on their structural and magnetic properties. All the samples were synthesized by calcination of the related oxalates at 1200 °C in order to ensure the complete decomposition of the oxalates. Five phase regions, namely an A-type hexagonal, a B-type monoclinic, a C-type cubic solid solution and two biphasic mixtures of the former three phase fields were detected in this system. The magnetic susceptibility measurements showed the presence of antiferromagnetic interactions in all samples. The Curie-Weiss temperature shows a nonlinear dependence on concentration. Deduced effective magnetic moments are close to the free ion values. 相似文献
2.
V.K. Sharma 《Journal of Physics and Chemistry of Solids》2009,70(6):941-947
In this paper we report the effect of microstructural characteristics on the magnetic properties of sol-gel synthesized Mn-doped ZnO. The microstructural characteristics of the samples (e.g., grain sizes and their distribution) have been varied by changing the sintering temperature (TS) and sintering duration (TH). Weak room temperature ferromagnetism (RTFM) has been observed in the samples sintered for ∼8 h at 500, 600, 700, 800 and 900 °C. The ferromagnetic fraction and the saturation magnetization, however, first increase as TS increases from 500 to 600 °C and after that both start decreasing. On the other hand, the samples sintered for ∼12 h at the same temperatures show paramagnetic behavior at room temperature. Field emission scanning electron microscope (FESEM) results show enhancement in the grain sizes with the increase in both TS and TH. Energy dispersive X-ray (EDAX) results show increase in the oxygen content in the sample with increase in both TS and TH. X-ray diffractometer (XRD) measurements reveal that the basic crystal structure of all the samples corresponds to the wurtzite structure of pure ZnO together with some minor impurities. The correlation between the observed magnetic properties and the microstructural characteristics of the samples has been discussed in this paper. 相似文献
3.
Sagar E. Shirsath B.G. Toksha S.M. Patange Ganesh S. Jangam 《Journal of Physics and Chemistry of Solids》2010,71(12):1669-1675
The ferrite samples of a chemical formula Ni0.5−xMnxZn0.5Fe2O4 (where x=0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) were synthesized by sol-gel auto-combustion method. The synthesized samples were annealed at 600 °C for 4 h. An analysis of X-ray diffraction patterns reveals the formation of single phase cubic spinel structure. The lattice parameter increases linearly with increase in Mn content x. An initial increase followed by a subsequent decrease in saturation magnetization with increase in Mn content is observed showing inverse trend of coercivity (Hc). Curie temperature decreases with increase in Mn content x. The initial permeability is observed to increase with increase in Mn content up to x=0.3 followed by a decrease, the maximum value being 362. Possible explanation for the observed structural, magnetic, and changes of permeability behavior with various Mn content are discussed. 相似文献
4.
A systematic study of magnetoelectric composite system (x) CoFe2O4+(1−x) Pb(Mg1/3Nb2/3)0.67Ti0.33O3 with x=0, 0.15, 0.30, 0.45 and 1 was carried out. The lattice strain was calculated using Williamson and Hall equation, which depends on the content of constituent phases in composites. The microstructure was studied using scanning electron microscopy. The ferroelectric transition temperature was independent of the content of individual phases, suggesting that the ferroelectric character is maintained in the composite. Observed P–E and M–H loops indicate that the multiferroic nature of magnetoelectric ceramics is dependent on the content of individual phases. The variation of magnetostriction with dc magnetic field was studied. The maximum magnetoelectric voltage coefficient of 7.2 mV/cm Oe is obtained for the synthesized composites. The magnetoelectric measurements are well explained with magnetostrictive behavior of the magnetic phase. 相似文献
5.
Gagan Kumar Jagdish Chand R.K. Kotnala 《Journal of Physics and Chemistry of Solids》2010,71(3):375-380
In the present work, mixed magnesium-manganese ferrites of composition Mg0.9Mn0.1Al0.3CozFe1.7−zO4 where z=0.3, 0.5 and 0.7 have been synthesized by the citrate precursor technique. X-ray diffraction patterns of the samples confirmed the formation of single-phase spinel structure. The ferrites have been investigated for their electric and magnetic properties such as dc resistivity, Curie temperature, saturation magnetization, initial permeability and relative loss factor (RLF). Fairly constant value of initial permeability over a wide frequency range (0.1-20 MHz) and low values of the relative loss factor of the order of 10−4-10−5, in the frequency range 0.1-30 MHz, are the cardinal achievements of the present investigation. In addition to this, initial permeability was found to increase with an increase in temperature while RLF was observed to be low at these temperatures. The dc resistivity and Curie temperature were found to increase with an increase in cobalt content. The mechanisms contributing to these results are discussed in detail in this paper. 相似文献
6.
The effect of co-dopant M (M=gallium (Ga), aluminum (Al), and scandium (Sc)) on the formation, crystallite growth, optical band gap, photocatalytic activity, and phase stability of anatase-type titanium dioxide solid solutions (Ti1−2XNbXMXO2) containing the same amount of dopant niobium (Nb) that were directly formed as nanoparticles under mild hydrothermal conditions at 180 °C for 5 h was investigated. The composition range X of the anatase-type solid solutions (Ti1−2XNbXMXO2) depended on the co-dopant M, i.e., X=0.15-0.20 for M=Ga and Al, and X=0.33 for M=Sc. A remarkable increase in the lattice parameter c0 was detected in the solid solutions co-doped with M=Sc. The increase in the amount of co-dopant M=Ga and Al enhanced the crystallite growth of the anatase-type solid solutions under the hydrothermal conditions. The photocatalytic activity of the solid solutions (Ti0.80Nb0.10M0.10O2) co-doped with M=Sc, Ga, and Al increased in that order. The co-dopant M=Ga promoted the anatase-to-rutile phase transformation of the solid solutions at lower temperature. 相似文献
7.
Prakash Chandra Sati Manisha AroraSunil Chauhan Manoj KumarSandeep Chhoker 《Journal of Physics and Chemistry of Solids》2014
Bi1−xDyxFeO3 (x=0.0, 0.03, 0.05, 0.07, 0.10 and 0.12) ceramics were synthesized by solid state reaction method. Effects of Dy substitution on structural distortion, magnetic and optical properties of BiFeO3 were examined by X-ray diffraction, Raman and UV–Visible spectroscopy. The samples were found to crystallize in rhombohedral structure of BiFeO3 with R3c space group. The reduction in lattice parameters and unit cell volume indicate the distortion in FeO6 octahedra of the rhombohedral structure without any signature of phase transformation up to x=0.12. The predictable weak ferromagnetic hysteresis loops can be observed in the Dy doped samples with maximum remnant magnetization of 0.2103 emu/g for x=0.12. The weak ferromagnetism is ascribed to the suppressed spiral spin structure and magnetically active characteristic of Dy3+ ions together with ferromagnetic coupling between Dy3+ and Fe3+ ions. With optical band gap in visible region, Dy doped BiFeO3 ceramics are potential material for optoelectronic device and solar cell applications. 相似文献
8.
Preparing M-type barium hexaferrite and improving the magnetic response of natural ferrites by incorporating barium carbonate (BaCO3) is ever-demanding. Series of barium carbonate doped ferrites with composition (100−x)Fe3O4·xBaCO3 (x=0, 10, 20, 30 wt%) are prepared through solid state reaction method and sintered gradually at temperatures of 800 and 1000 °C. Nanoparticles of natural ferrite and commercial BaCO3 are used as raw materials. Impacts of BaCO3 on structural and magnetic properties of these synthesized ferrites are inspected. The obtained ferrites are characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM) at room temperature. Uniform barium hexaferrite particles in terms of both morphology and size are not achieved. The average crystallite size of BaFe12O19 is observed to be within 30–600 nm. The sintering process results phase transformation from Fe3O4 (magnetite) to α-Fe2O3 (hematite) and the formation of hexagonal barium ferrite crystals. The occurrence of barium crystal is found to enhance with the increase of BaCO3 concentrations up to 20 wt% and suddenly drop at 30 wt%. Saturation and remanent magnetization of the doped ferrites are significantly augmented up to 16.37 and 8.92 emu g−1, respectively compared to their pure counterpart. Furthermore, the coercivity field is slightly decreased as BaCO3 concentrations are increased. BaCO3 mediated improvements in the magnetic response of natural ferrites are demonstrated. 相似文献
9.
The transport properties of Sr0.98La0.02SnO3−δ in the system Sr1−xLaxSnO3−δ, after which the pyrochlore La2Sn2O7 appears, were investigated over the temperature range 4.2-300 K. The oxide was found to be n-type semiconductor with concomitant reduction of Sn4+ into Sn2+. The magnetic susceptibility was measured down to 4.2 K and is less than 3×10−5 emu cgs mol−1 consistent with itinerant electron behavior. The electron is believed to travel in a narrow band of Sn:5s character with an effective mass ∼4 mo. The highest band gap is 4.32 eV and the optical transition is directly allowed. A further indirect transition occurs at 4.04 eV. The electrical conductivity follows an Arrhenius-type law with a thermal activation of 40 meV and occurs by small polaron hopping between nominal states Sn4+/2+. The linear increase of thermo-power with temperature yields an electron mobility μ300 K (2×10−4 cm2 V−1 s−1) thermally activated. The insulating-metal transition seems to be of Anderson type resulting from random positions of lanthanum sites and oxygen vacancies. At low temperatures, the conduction mechanism changes to a variable range hopping with a linear plot Ln ρ−1 vs. T−4. The photo electrochemical (PEC) measurements confirm the n-type conductivity and give an onset potential of −0.46 VSCE in KOH (1 M). The Mott-Schottky plot C−2-V shows a linear behavior from which the flat band potential Vfb=+0.01 VSCE at pH 7 and the doping density ND=1.04×1021 cm−3 were determined. 相似文献
10.
M. Penchal Reddy G. Balakrishnaiah M. Venkata Ramana K.V. Siva Kumar R. Ramakrishna Reddy 《Journal of Physics and Chemistry of Solids》2010,71(9):1373-4354
Polycrystalline NiCuZn soft ferrites with stoichiometric iron were prepared by a novel microwave sintering method. The powders were calcined, compacted and sintered at 950 °C for 30 min in a microwave sintering furnace. X-ray diffraction patterns confirm the formation of single phase cubic spinel structure. The grain size was estimated using SEM micrographs. The lattice constant is found to increase with increase in zinc concentration. The sintered ferrites have been investigated for their physical, magnetic and electrical properties such as bulk density, X-ray density, porosity, anisotropy constant, initial permeability, saturation magnetization, DC resistivity, dielectric constant and dielectric loss as a function of zinc concentration. Permeability, saturation magnetization, dielectric constant and dielectric loss were found to increase while DC resistivity was found to decrease with the replacement of Zn with Ni. The present series of ferrites are found to posses properties that are suitable for the core materials in multilayer chip inductors. 相似文献
11.
A. Martínez-de la Cruz F.E. Longoria Rodríguez 《Journal of Physics and Chemistry of Solids》2008,69(4):830-834
Electrochemical lithium insertion into (PO2)4(WO3)2m, where m=9 and 10, has allowed the determination of several phases Lix(PO2)4(WO3)2m between 3.4 and 0.01 V vs Li+/Li0. After the first cycle the electrochemical system was unable to maintain the high specific capacity of the cells (540 Ah/kg) due to irreversible processes. Nevertheless at high voltage values, above 1.4 V vs Li+/Li0, the lithium insertion proceeded through a reversible mechanism. By means of X-ray diffraction experiments we have detected the nature of different phases Lix(PO2)4(WO3)2m formed and we have established a correlation with the reversible/irreversible processes detected during the electrochemical insertion. 相似文献
12.
Room temperature multiferroic electroceramics of Gd doped BiFeO3 monophasic materials have been synthesized adopting a slow step sintering schedule. Incorporation of Gd nucleates the development of orthorhombic grain growth habit without the appearance of any significant impurity phases with respect to original rhombohedral (R3c) phase of un-doped BiFeO3. It is observed that, the materials showed room temperature enhanced electric polarization as well as ferromagnetism when rare earth ions like Gd doping is critically optimized (x=0.15) in the composition formula of Bi1+2xGd2x/2Fe1−2xO3. We believe that magnetic moment of Gd+3 ions in Gd doped BiFeO3 tends to align in the same direction with respect to ferromagnetic component associated with the iron sub lattice. The dielectric constant as well as loss factor shows strong dispersion at lower frequencies and the value of leakage current is greatly suppressed with the increase in concentration of x in the above composition. Addition of excess bismuth and Gd (x=0.1 and 0.15) caused structural transformation as well as compensated bismuth loss during high temperature sintering. Doping of Gd in BiFeO3 also suppresses spiral spin modulation structure, which can change Fe-O-Fe bond angle or spin order resulting in enhanced ferromagnetic property. 相似文献
13.
Aqueous electrochemical insertion of M+ (Na+ and H+) species into WO3(4,4′-bipyridyl)0.5 has been carried out. The chemical states and structure of the resulting product were analysed by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). XPS showed the presence of W6+ as well as the usual reduced W species (W5+) which is responsible for a change in colour. Moreover, the presence of these intercalates correlates with the evolution of the reduced W species. The bulk structure of the layered hybrid, as determined by powder X-ray diffraction, showed no alteration after electrochemistry, in contrast to the same measurements on tungsten trioxide (WO3). This however concurs with single-crystal X-ray studies, which show little change in lattice parameters with Na+ insertion. Four-probe resistance measurements of the layered hybrid coated film display a drop in resistance after electrochemistry, which can be attributed to the injection of charge-carriers into the conduction band. 相似文献
14.
The effect of indium (In) substitution in the dynamics of structure and ferrimagnetism of yttrium iron garnet (YIG) employing sintering temperature as a temporary agent of composition and structural changes was reported in this study. The nanoparticles of YIG powder samples with various In content (x=0.0–0.4) were prepared via the mechanical alloying (MA) technique. A brief, yet revealing characterization of the samples was carried out via transmission electron microscope, X-ray diffraction, Raman spectroscopy, B–H Hysteresisgraph, and LCR-metre. The X-ray diffraction analysis of the samples prepared via the MA indicates the formation of single phase YIG structure at much lower sintering temperature than that in the conventional ceramic technique. The lattice constant increases as In content increases which obeys Vegard's Law due to the larger In3+ ions replacing the smaller Fe3+ ions. The saturation induction increased reaching about 699.1 G for x=0.3 and decreased with further In substitution. Three stages of ordered magnetism formation were identified which attributed to development of crystallinity and larger grains for magnetic domain accommodation. The Curie temperature shows a decrement in their values with In content due to weakening of superexchange interactions. Raman shifts from 268.1 to 272.2 cm−1 with increasing In content were observed due to stress developed in the YIG crystal structure. 相似文献
15.
K RuckW Pitschke G Krabbes M WolfD Eckert K.-H Müller 《Journal of Physics and Chemistry of Solids》2002,63(10):1901-1907
Phases of the composition Ca1−x−yMgxCu2+yO3 have been prepared for the first time. The compounds are isostructural with the known end-members CaCu2O3 and MgCu2O3 showing a two-leg spin-ladder-like connection of copper and oxygen atoms within the Cu2O3-layer. Opposite the spin ladders this layer is folded, which results in a long-range antiferromagnetic ordering of these phases. The Néel temperature can be adapted by variation of x in Ca1−x−yMgxCu2+yO3 between 24 and 80 K. Several structural features, which influence the magnetic ordering, are discussed. 相似文献
16.
In this work, we report the magnetic properties of isotropic M-type SrFe12−xAlxO19 (x=0.0,1.5) hexaferrites synthesized by means of Pechini method. A polycrystalline distribution of fine grains was verified by Transmission Electron Microscopy for both compositions, with average sizes below 60 nm. Remarkable coercivity values within the range 500–850 kA/m were attained as a consequence of a combined effect of grain size refinement together with an enhancement of the anisotropy field afforded by the incorporation of the Al3+ cations into the hexagonal crystal structure. 相似文献
17.
The effects of K doping in the A-site on the structural, magnetic and magnetocaloric properties in La0.65Ca0.35−xKxMnO3 (0?x?0.2) powder samples have been investigated. Our samples have been synthesized using the solid-state reaction method at high temperature. The parent compound La0.65Ca0.35MnO3 is an orthorhombic (Pbnm space group) ferromagnet with a Curie temperature TC of 248 K. X-ray diffraction analysis using the Rietveld refinement show that all our synthesized samples are single phase and crystallize in the orthorhombic structure with Pbnm space group for x?0.1 and in the rhombohedral system with R3¯c space group for x=0.2 while La0.65Ca0.2K0.15MnO3 sample exhibits both phases with different proportions. Magnetization measurements versus temperature in a magnetic applied field of 50 mT indicate that all our investigated samples display a paramagnetic-ferromagnetic transition with decreasing temperature. Potassium doping leads to an enhancement in the strength of the ferromagnetic double-exchange interaction between Mn ions, and makes the system ferromagnetic at room temperature. Arrott plots show that all our samples exhibit a second-order magnetic-phase transition. The value of the critical exponent, associated with the spontaneous magnetization, decreases from 0.37 for x=0.05 to 0.3 for x=0.2. A large magnetocaloric effect (MCE) has been observed in all samples, the value of the maximum entropy change, |ΔSm|max, increases from 1.8 J/kg K for x=0.05 to 3.18 J/kg K for x=0.2 under a magnetic field change of 2 T. For x=0.15, the temperature dependence of |ΔSm| presents two maxima which may arise from structural inhomogeneity. 相似文献
18.
N.A. Bakr V.S. Waman R.R. Hawaldar V.G. Sathe S.R. Jadkar 《Journal of Physics and Chemistry of Solids》2011,72(6):685-691
Hydrogenated nanocrystalline silicon (nc-Si:H) thin films were deposited using HW-CVD technique at various deposition pressures. Characterisation of these films from Raman spectroscopy revealed that nc-Si:H thin films consist of a mixture of two phases, crystalline phase and amorphous phase containing small Si crystals embedded therein. We observed increase in crystallinity in the films with increase in deposition pressure whereas the size of Si nanocrystals was found ∼2 nm over the entire range of deposition pressure studied. The FTIR spectroscopic analysis showed that with increasing deposition pressure the predominant hydrogen bonding in the films shifts from, Si-H to Si-H2 and (Si-H2)n complexes and the hydrogen content in the films was found in the range 6.2-9.3 at% over the entire range of deposition pressure studied. The photo and dark conductivities results also indicate that the films deposited with increasing deposition pressure get structurally modified. It has been found that the optical energy gap range was between 1.72 and 2.1 eV with static refractive index between 2.85 and 3.24. From the present study it has been concluded that the deposition pressure is a key process parameter to induce the crystallinity in the Si:H thin films using HW-CVD. 相似文献
19.
M. Ito N. Tuji H. Adachi K. Namikawa Y. Murakami Y. Tokura 《Journal of Physics and Chemistry of Solids》2004,65(12):1993-1997
X-ray magnetic diffraction (XMD) experiments of ferromagnetic YTiO3 were performed. The orbital-magnetic form factor (L) and the spin-magnetic form factor (S) were individually measured by utilizing the LS separation method of the XMD. The experiments consisted of two parts. The first was the measurement of the orbital-magnetic form factor to examine whether the orbital moment of this compound was quenched or not. The second was the measurement of the spin-magnetic form factor to examine whether the ordered orbital of Ti-3d electrons was observed by the XMD. The result of the first experiment suggested quenching of the orbital moment. In the second experiment, the spin-magnetic form factor was observed for the total 22 reciprocal-lattice points. Calculated spin-magnetic form factor with a model wave function of the ordered orbital reproduced the observed one well. This result shows that the ordered orbital of Ti-3d electrons can be observed by the XMD. 相似文献
20.
Interaction of copper and NO2: Effect of joint presence of SO2, relative humidity and temperature 总被引:1,自引:0,他引:1
L. Mariaca D. de la Fuente S. Feliu Jr. J. Simancas J.A. Gonzlez M. Morcillo 《Journal of Physics and Chemistry of Solids》2008,69(4):895-904
This paper reports laboratory tests involving the dry deposition on copper surfaces of NO2, alone and in combination with SO2, at different concentrations (200 and 800 μg m−3), temperatures (15, 25 and 35 °C) and relative humidities (50%, 70% and 90%). Gravimetric results and characterisation of the corrosion products by optical microscopy, scanning electron microscopy (SEM/EDX), grazing incidence X-ray diffraction (GIXD) and X-ray photoelectron spectroscopy (XPS) show that the corrosive effect of NO2 acting alone depends greatly on the RH. At 90% RH copper behaves in the same way as in unpolluted atmospheres, while at lower RH localised attack is detected. Analysis reveals the presence of basic copper nitrate (gerhardtite, Cu2(OH)3NO3). However, in SO2-polluted atmospheres no differential behaviour with RH or temperature is observed. In these atmospheres copper corrosion is similar to that obtained in unpolluted or in NO2-polluted atmospheres at high RH, although GIXD detects basic copper sulphate (posnjakite, Cu4(OH)6SO4·2H2O). In the case of mixed atmospheres (SO2+NO2) a significant accelerating effect is observed when [NO2]>[SO2]. Otherwise an inhibitive effect is detected. At high RH in the presence of SO2, NO2 favours SO2 oxidation and finally sulphuric acid formation, which attacks the cuprite layer. S-containing compounds, especially basic copper sulphate, are easily detected by GIXD and XPS in the outermost corrosion product layer. However, at low RH, NO2 reacts preferentially with adsorbed water to produce nitrous and nitric acids that attack the cuprite layer. In this case, an outer corrosion product layer containing copper nitrite (soluble) and basic copper nitrate is formed over an intermediate layer that contains significant amounts of basic copper sulphate from the previous interaction of sulphuric acid and cuprite. 相似文献