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1.
Polycrystalline Sr2Fe1−xGaxMoO6 (0 ≤ x ≤ 0.6) materials have been synthesized by solid state reaction method and studied by neutron powder diffraction (NPD) and magnetization measurements. Rietveld analysis of the temperature dependent NPD data shows that the compounds crystallize in the tetragonal symmetry in the space group I4/m. The anti-site (AS) defects concentration increases with Ga doping, giving rise to highly B-site disordered materials. Ga doping at the Fe-site decreases the cell volume. The evolution of bond lengths and the cation oxidation states was determined from the Rietveld refinement data. The saturation magnetization and Curie temperature decreased with the increasing Ga content in the samples. Low temperature neutron diffraction data analysis and magnetization measurements confirm the magnetic interaction as ferrimagnetic in the sample.  相似文献   

2.
Manoj Kumar 《Materials Letters》2007,61(10):2089-2092
xCuFe2O4-(1 − x)BiFeO3 spinel-perovskite nanocomposites with x = 0.1, 0.2, 0.3 and 0.4 were prepared using citrate precursor method. X-ray diffraction (XRD) analysis showed phase formation of xCuFe2O4-(1 − x)BiFeO3 calcined at 500 °C. Transmission electron microscopy (TEM) shows formation of nanocrystallites of xCuFe2O4-(1 − x)BiFeO3 with an average particle size of 40 nm. Variation of dielectric constant and dielectric loss with frequency showed dispersion in the low frequency range. Coercivity, saturation magnetization and squareness have been found to vary with concentration of ferrite phase and annealing temperature due to the increase in crystallite size. Squareness and coercivity increased with an increase in annealing temperature up to 500 °C and then decreased with a further increase in temperature to 600 °C. Magnetoelectric effect of the nanocomposites was found to be strongly depending on the magnetic bias and magnetic field frequency.  相似文献   

3.
The grain size and the density of the Zn1 − xSnxO (0 ≤ x ≤ 0.05) samples decreased with increasing SnO2 content. The addition of a small amount of SnO2 (x ≤ 0.01) to ZnO led to an increase in both the electrical conductivity and the absolute value of the Seebeck coefficient, resulting in a significant increase in the power factor. The thermoelectric power factor was maximized to a value of 1.25 × 10−3 Wm−1 K−2 at 1073 K for the Zn0.99Sn0.01O sample.  相似文献   

4.
Nanocrystalline nickel ferrite with different concentration of Ni and Zn (NixZn1 − xFe2O4 where x = 0.1, 0.3, 0.5) were synthesized using chemical co-precipitation method. The effect of doping ion concentration on physical properties like crystalline phase, crystallite size, particle size, and saturation magnetization are investigated. The X-ray diffraction pattern confirms the synthesis of single crystalline NixZn1 − xFe2O4 nanoparticles. The lattice parameter decreases with increase Ni content resulting in reduction of lattice strain. HRTEM images revealed that the as-prepared nanoparticles were crystalline with particle size distribution in 10-30 nm range. The saturation magnetization show the superparamagnetic nature of sample for x = 0.1 and x = 0.3 whereas for x = 0.5, the material is ferromagnetic. The saturation magnetization value is 23.95 emu/gm for Ni0.1Zn0.9Fe2O4 sample and it increases with increase in Ni content.  相似文献   

5.
CaRuO3-CaTiO3 ceramic composites were prepared by sintering for short times for potential applications in the areas of electronic ceramics. Scanning electron microscopy and energy dispersive X-ray analysis showed two separate phases, CaRuO3 and CaTiO3 in the composite. Conductivity data, measured by the four-probe method, showed that the composites have high electrical conductivity when x ≥ 0.19 in xCaRuO3-(1 − x)CaTiO3 composites. Furthermore, the nanoparticle of calcium ruthenate prepared by reverse micelle synthesis was used to be conductive agent for the composite. The result shows that the use of nano-sized calcium ruthenate enabled higher electrical conductivity to be maintained down to x = 0.09.  相似文献   

6.
Electrical and magnetoelectric properties of magnetoelectric (ME) composites containing barium titanate as electrical component and a mixed Ni-Co-Mn ferrite as the magnetic component are reported. The ME composites with a general formula (x)BaTiO3 + (1 − x)Ni0.94Co0.01Mn0.05Fe2O4 where x varies as 0, 0.55, 0.70, 0.85 and 1 were prepared by standard double sintering ceramic method. The presence of both the phases was confirmed by X-ray diffraction technique. The dc resistivity was measured as a function of temperature. The variation of dielectric constant (?) and loss tangent (tan δ) with frequency (100 Hz-1 MHz) and with temperature was studied. The conduction is explained on the basis of small polaron model based on ac conductivity measurements. The static value of ME conversion factor i.e. dc (ME)H was studied as function of intensity of magnetic field. The changes were observed in dielectric properties as well as ME effect as the molar ratio of the components was varied. A maximum value of ME conversion factor of 610 μV/cm Oe was observed in the case of a composite containing 15 mol% ferrite phase.  相似文献   

7.
Mass density, glass transition temperature and ionic conductivity are measured in xLi2O-(40 − x)Na2O-50B2O3-10Bi2O3 and xK2O-(40 − x)Na2O-50B2O3-10Bi2O3 glass systems with 0 ≤ x ≤ 40 mol%. The strength of the mixed alkali effect in Tg, dc electrical conductivity and activation energy has been determined in each glass system. The magnitudes of the mixed alkali effect in Tg for the mixed Li/Na glass system are much smaller than those in the mixed K/Na glasses. The impact of mixed alkali effect on dc electrical conductivity in mixed Li/Na glass system is more pronounced than in the K/Na glass system. The results are explained based on dynamic structure model.  相似文献   

8.
Nanocrystalline La1−xCdxFeO3 (0.0 ≤ x ≤ 0.3) solid solutions have been synthesized by a single-step solution combustion method at a relatively low temperature of 400 °C. The combustion-synthesized solid solutions were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and magnetic measurements. The crystal structure examined by XRD indicates that the samples were single-phase, and crystallize in an orthorhombic (space group, Pbnm no. 62) structure. The parent and doped compounds showed canted antiferromagnetic behavior associated with an increase in magnetic moment with Cd doping. The changes in magnetic properties of the materials are correlated to the changes in structural features resulting from the Rietveld structural refinement of the materials.  相似文献   

9.
The CuCr1−xRhxO2 series is investigated by X-ray diffraction, magnetization measurements and Raman spectroscopy on ceramic samples. It is found that a delafossite solid solution is maintained up to x = 0.2 in CuCr1−xRhxO2. The small observed variation in cell parameters is consistent with the small difference between the ionic radii of Cr3+ and Rh3+. A significant broadening of X-ray reflections is observed and when analyzed using the Williamson-Hall relationship showed that the strain generated by Rh substitution is strongly anisotropic, affecting mainly (Cr,Rh)-O bonds in the ab plane. Room temperature Raman spectra displayed three main Raman active modes. All modes shift to lower frequency and undergo significant changes in intensity with increasing Rh content, showing the effect of Rh atoms on the M3+-O bond strength. The magnetic behavior of CuCr1−xRhxO2 samples was investigated as a function of temperature and applied field. At high temperature paramagnetic behavior, and at low temperature, evidence for weak ferromagnetism, reinforced by a hysteresis loop at 4 K is observed. The magnetic behavior of CuCr1−xRhxO2 is attributed to the disorder of Cr and Rh in octahedral sites resulting in short-range Cr-O-Cr and Cr-O-Rh interactions, which give rise to short-range weak ferromagnetism.  相似文献   

10.
Single-crystal PbxLa1 − xTiO3 (PLT) nanorods of various La concentrations have been synthesized by polymer-assisted hydrothermal method. The nanorods have diameters of 25-60 nm and average lengths of 3 μm. With tetragonal lattices structures, the PLT nanorods grow along the (001) direction. As La concentration increasing, the tetragonality c/a decreases and the Raman mode E(1TO) becomes softening. PLT nanorods with various lengths and diameters have been prepared by using different polymer additives. To fabricate well-crystallized nanorods, an annealing process after the hydrothermal treatment is proved to be necessary.  相似文献   

11.
The Gd2(TixZr1 − x)2O7 (x = 0, 0.25, 0.50, 0.75, 1.00) ceramics were synthesized by solid state reaction at 1650 °C for 10 h in air. The relative density and structure of Gd2(TixZr1 − x)2O7 were analyzed by the Archimedes method and X-ray diffraction. The thermal diffusivity of Gd2(TixZr1 − x)2O7 from room temperature to 1400 °C was measured by a laser-flash method. The Gd2Zr2O7 has a defect fluorite-type structure; however, Gd2(TixZr1 − x)2O7 (0.25 ≤ x ≤ 1.00) compositions exhibit an ordered pyrochlore-type structure. Gd2Zr2O7 and Gd2Ti2O7 are infinitely soluable. The thermal conductivity of Gd2(TixZr1 − x)2O7 increases with increasing Ti content under identical temperature conditions. The thermal conductivity of Gd2(TixZr1 − x)2O7 first decreases gradually with the increase of temperature below 1000 °C and then increases slightly above 1000 °C. The thermal conductivity of Gd2(TixZr1 − x)2O7 is within the range of 1.33 to 2.86 W m− 1 K− 1 from room temperature to 1400 °C.  相似文献   

12.
Spinel ferrite Cox(Cu0.5Zn0.5)1−xFe2O4 over a compositional range 0 < x < 1 was prepared using a simple hydrothermal method. Particle sizes could be varied from 14 to 25 nm by changing the x value. X-ray diffraction results confirmed that all the as-prepared nanoparticles revealed typical spinel structure and transmission electron microscopy images showed that the particle size of the samples increased with increasing x value. The magnetic properties of the as-prepared Cox(Cu0.5Zn0.5)1−xFe2O4 nanoparticles have been systematically examined. The maximum saturation magnetization existed at the highest Co content (x = 1). The electromagnetic properties of all the samples have been measured by an Agilent network analyzer and the results showed that Co0.1(Cu0.5Zn0.5)0.9Fe2O4 possessed the best microwave absorbing properties.  相似文献   

13.
A. Biju 《Materials Letters》2007,61(3):648-654
The structural, electrical and superconducting properties of Bi1.7Pb0.4Sr2 − xYbxCa1.1Cu2.1Oy system has been studied for different Yb concentrations. The samples are prepared by solid state synthesis in the polycrystalline bulk form. Structural analysis by X-ray diffraction, microstructural examination by SEM and measurements of electrical and superconducting properties have been conducted to study the effects of Yb substitution at Sr site. The critical temperature (TC) and critical current density (JC) are found to increase drastically with Yb substitution. Maximum values of TC and JC are observed for x = 0.3 and x = 0.2 respectively. The increase in TC and JC is explained due to the substitution effect of Yb3+ in place of Sr2+ and consequent change in the hole concentration in the CuO2 planes. Above the optimum levels TC and JC begin to reduce due to secondary phase formation. A metal-insulator transition originating from the change of carrier concentration is found to occur at higher doping level (x > 0.5).  相似文献   

14.
Up to 10 at.% of copper readily substitutes for cerium in ceria. It is found that at oxygen partial pressures between 0.21 atm and 10−5 atm, CuxCe1−xO2−δ (0 ≤ x ≤ 0.10) solid solution behave as an oxide-ion electrolyte. Interestingly, Cu0.10Ce0.90O2−δ exhibits the oxide-ion conductivity of ca. 10−4 Ω−1 cm−1 at 600 °C at an oxygen partial pressure of 10−5 atm.  相似文献   

15.
Differential scanning calorimetry (DSC), infrared (IR) and direct current (DC) conductivity studies have been carried out on (100 − 2x)TeO2-xAg2O-xWO3 (7.5 ≤ x ≤ 30) glass system. The IR studies show that the structure of glass network consists of [TeO4], [TeO3]/[TeO3+1], [WO4] units. Thermal properties such as the glass transition (Tg), onset crystallization (To), thermal stability (ΔT), glass transition width (ΔTg), heat capacities in the glassy and liquid state (Cpg and Cpl), heat capacity change (ΔCp) and ratios Cpl/Cpg of the glass systems were calculated. The highest thermal stability (237 °C) obtained in 55TeO2-22.5Ag2O-22.5WO3 glass suggests that this new glass may be a potentially useful candidate material host for rare earth doped optical fibers. The DC conductivity of glasses was measured in temperature region 27-260 °C, the activation energy (Eact) values varied from 1.393 to 0.272 eV and for the temperature interval 170-260 °C, the values of conductivity (σ) of glasses varied from 8.79 × 10−9 to 1.47 × 10−6 S cm−1.  相似文献   

16.
Effects of the partial substitution of W5+,6+ for Mo5+,6+ on the structural and physical properties of Ba2CrMoO6 have been investigated. Polycrystalline Ba2CrMo1 − xWxO6samples have been prepared by sol-gel method in a stream of 5% Ar/H2 gas at various sintering temperatures. Rietveld analysis of X-ray diffraction patterns shows a partial disorder of Mo/W and Cr on the B sites of the double perovskite, which plays a dominant role in the structural and magnetic properties of these compounds. The symmetry is cubic (Fm3?m) for all samples, and no phase transition was detected for Ba2CrMo1 − xWxO6. The Curie temperature TC has been analyzed by two methods: a linear extrapolation of M(T) to zero magnetization and the thermodynamic model. The experimental results indicate that TC decrease from 335 K (x = 0) to 285 K (x = 0.5) with increasing W substitution independently of the method used to obtain TC. A systematic decrease in saturation magnetization, Ms with increasing W substitution has been observed in this solid solution series. This decrease of magnetization arises from the disorder at the Cr and Mo/W sites. Electrical properties change as well strongly along the series.  相似文献   

17.
La2−xBaxMo2O9−x/2 (x ≤ 0.18) have been prepared by solid state reaction method. The lattice parameter of La2−xBaxMo2O9−x/2 (x ≤ 0.18) determined by XRD data refinement shows a linear dependence on the dopant Ba content x. For the specimen with a La/Ba molar ratio of 0.18-0.2, additional reflection of secondary phase exists in the XRD pattern, so the value of solubility limit for Ba in La2Mo2O9 is defined in range of 0.18 < x < 0.2. As the replacement degree of La3+ by Ba2+ increases, the bulk conductivity of La2−xBaxMo2O9−x/2 (x ≤ 0.18) decreases initially and then increases, a minimum value at La1.9Ba0.1Mo2O8.95 exists. Hebb-Wagner studies in argon atmosphere, which use an oxide-ion blocking electrode, show that La2−xBaxMo2O9−x/2 (x ≤ 0.18) are predominantly oxide-ion conducting in the temperature ranging from 773 to 1173 K. The average thermal expansion coefficient of La1.84Ba0.16Mo2O8.92 determined by high-temperature XRD was deduced as great as 17.5 × 10−6 K−1 between 298 and 1173 K.  相似文献   

18.
The BiCoxFe1 − xO3 samples have been successfully synthesized by hydrothermal process. The resulting products were characterized by X-ray powder diffraction (XRD), energy dispersive X-ray (EDS), differential thermal analysis (DTA), and physical property measurement system (PPMS).It was found that the magnetization of the obtained products was greatly enhanced by Co substituting for Fe ions. Furthermore, the value of magnetism of BiCoxFe1 − xO3 samples can be adjusted by Fe doping concentration. DTA curve indicates the ferroelectric properties of the obtained BCFO samples are not affected by Co substitution. Therefore, it would be interesting to realize thin films with similar compositions and study their properties in the interest of device applications.  相似文献   

19.
A newly substituted series of perovskites, BixLa2−xMnMO6 with M = Ni, Co and x = 0.25, 0.50, were synthesized using a citrate sol-gel technique. The crystal structure, established from neutron diffraction, is a distorted double perovskite with partial transition metal B-site ordering. These perovskites crystallize in the centrosymmetric space group, P21/n, with structures that are similar to the x = 0 end members. All samples are prone to non-stoichiometry involving substitution of Mn onto the Ni/Co sites, in addition to varying degrees of antisite disorder. The neutron powder diffraction and magnetization measurements reveal ferromagnetism in all samples with ordering temperatures between 220 K and 280 K. The M = Co samples have lower Curie temperatures, but higher coercivities. There is a clear link between the degree of transition metal site disorder and the saturation magnetization values. Electrical measurements demonstrate the presence of mixed ionic and electronic conductivity.  相似文献   

20.
(1 − x)Ba(Zn1/3Ta2/3)O3-xBaTi4O9 (0.1 ≤ x ≤ 0.85) composites are prepared by mixing 1150 °C-calcined BaTi4O9 with 1150 °C-calcined Ba(Zn1/3Ta2/3)O3 powders. The crystal structure, microwave dielectric properties and sinterabilites of the (1 − x)Ba(Zn1/3Ta2/3)O3-xBaTi4O9 ceramics have been investigated. X-ray diffraction patterns reveal that BaTi4O9, ordered and disordered Ba(Zn1/3Ta2/3)O3 phases exist independently over the whole compositional range. The sintering temperatures of (1 − x)Ba(Zn1/3Ta2/3)O3-xBaTi4O9 ceramics are about 1240 - 1320 °C and obviously lower than those of Ba(Zn1/3Ta2/3)O3 ceramics. The dielectric constants (?r) and the temperature coefficient of resonant frequency (τf) of (1 − x)Ba(Zn1/3Ta2/3)O3-xBaTi4O9 ceramics increase with the increase of BaTi4O9 content. Nevertheless, the bulk densities and the quality values (Q × f) of (1 − x)Ba(Zn1/3Ta2/3)O3-xBaTi4O9 ceramics increase with the increase of Ba(Zn1/3Ta2/3)O3 content. The results are attributed to the higher density and quality value of Ba(Zn1/3Ta2/3)O3 ceramics, the better grain growth, and the densification of sintered specimens added a small BaTi4O9 content. The (1 − x)Ba(Zn1/3Ta2/3)O3-xBaTi4O9 ceramic with x = 0.1 sintered at 1320 °C exhibits a ?r value of 31.5, a maximum Q × f value of 68500 GHz and a minimum τf value of 4.1 ppm/°C.  相似文献   

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