首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
《Ceramics International》2022,48(13):18784-18792
Bulk Cr1-xMnxO2 samples are prepared by high pressure synthesis technology. The crystal structure, magnetic properties and electronic structure of the samples are investigated by experiments and theoretical calculation. The crystal structure of the samples are indexed to a rutile structure with space group P42/mnm. The lattice parameter a of the samples remains basically unchanged in accordance with Vegard's law, but the lattice parameter c decreases due to increasing Mn dopant content (x) as well as strong Metal–Metal bonding along the c-axis. The saturation magnetization of the Cr1-xMnxO2 samples decreases with an increase in x. According to XPS analysis, there is electron transfer between Mn and Cr in Cr1-xMnxO2. Mn exists as Mn2+ and Mn3+ions, and part of Cr is oxidized to Cr6+. Based on the XPS analysis, the magnetic moment of Cr1-xMnxO2 is calculated and its value is in accordance with the experimental data.  相似文献   

2.
In this paper, the crystal structure, vacancy defect, local electron density and magnetic properties of Gd1-xCaxCrO3 (0 ≤ x ≤ 0.3) polycrystalline samples were investigated systematically. The crystal structural analyses show that all the samples are orthorhombic phase and a structural distortion happens around x = 0.3. Due to the formation of Cr4+ ions, both the lattice constant and the Cr–O bond length decrease. The results of positron annihilation spectrum reveals that the vacancy defect concentration increases and the local electron structure changes with the introduction of Ca2+ ions. The field-cooled (FC) and zero-field cooled (ZFC) curves of Gd1-xCaxCrO3 samples measured under H = 100 Oe exhibits negative magnetization characteristics due to the interaction between Gd3+ and Cr3+ ions, and the magnetism can be affected by the structural distortion.  相似文献   

3.
《Ceramics International》2022,48(22):33135-33142
This investigation highlights the significant influences of alkaline earth ion substitution for Gd on the structure, vacancy defects, magnetic and dielectric properties in GdMnO3 (GMO) ceramics synthesized using the solid-state reaction method. The structure measurements indicate that all of the Gd0.90A0.10MnO3 (A = Ca, Sr, Ba) samples show a single phase structure, and the introduction of A2+ ion induces structure distortion. A2+ ions substitution increases the Mn4+ ion concentration in GMOs, but has no significant effect on the oxygen vacancy concentration. All samples with irregular grain shapes have dense microstructures, and A2+ ion substitution inhibits grain growth. Positron annihilation experimental results indicate that A2+ ion substitution can increase the vacancy size and concentration, while the vacancy concentration increases first and then decreases with increasing A2+ ion radius. The evolution of the temperature- and magnetic field-dependent magnetization curves shows that A2+ ion substitution could obviously affect the magnetic state of GMOs, and improve the magnetic transition temperature and magnetization of Gd0.90A0.10MnO3. The dielectric measurements reveal that the A2+ ion substituted samples exhibit giant dielectric constant characteristics over a broad frequency range. It is found that the enhanced magnetization of Gd0.90A0.10MnO3 has a close relationship with the vacancy concentration, and the giant dielectric constant behaviors in Gd0.90A0.10MnO3 ceramics can be associated with the mixed-valent structure of Mn3+/Mn4+.  相似文献   

4.
《Ceramics International》2020,46(9):13350-13355
Ball- and sheet-like Sn1-xCrxO were successfully prepared by one-step hydrothermal method. The SEM and TEM results show that the diameter of ball-like unit is about 15 μm and the unit was assembled by several nanosheets with a thickness of about 0.5 μm. Raman pattern displays that there are two intense Raman mode Eg (~114 cm−1) and A1g (~211 cm−1) in the SnO, and the A1g peak shifted significantly. UV–Visible spectrum illustrates that the bandgap of the Cr-doped SnO firstly decreases and then increases as the Cr concentration increases, which is attributed to the sp-d exchange interactions and Burstein-Moss theory. The analysis of XPS also provides evidence for the incorporation of Cr into the system. Furthermore, it is found that oxygen vacancy (VO) decreases with the increase of Cr content. Based on Krӧger-Vink notation system, the competition mechanism between VO and VSn could explain the origin and variation of magnetism of Sn1-xCrxO from structural defects.  相似文献   

5.
《Ceramics International》2022,48(15):21622-21630
In this work, GdMnO3 ceramics were synthesized by solid state reaction and sol-gel methods, and the structure, defects and optical, dielectric and magnetic properties of the synthesized samples were comparatively investigated. The samples synthesized by different methods show a single phase structure without any detectable impurities. The SEM results suggest that the particle size of the specimen obtained by the solid phase route is on the micron scale, while that of the specimen fabricated by the sol-gel route is on the nanometer scale. Compared with the ceramic fabricated by solid-state reaction technology, the specimen synthesized by sol-gel technique possesses lower oxygen vacancies and Mn2+ concentration, and Mn3+ concentration. The positron annihilation analyses show that the cation vacancy concentration of the specimen synthesized by the solid phase approach is higher than that of the specimen synthesized via the sol-gel approach. The compound obtained by the solid phase reaction has better dielectric properties than that obtained with the sol-gel method. The magnetic transition temperature and the effective magnetic moment are influenced by the Mn ion valence state in GdMnO3. The stronger magnetization of the ceramic synthesized via the sol-gel approach is associated with the lower concentration of cation vacancies.  相似文献   

6.
The aim of this study is to evaluate the structural and magnetic properties of Ni–Zn doped ferrite with trivalent Al3+ and Cr3+ cations substitution in Ni0.6Zn0.4Fe2−xCrx/2Alx/2O4 (x=0, 0.1, 0.2, 0.3, 0.4 and 0.5) synthesized by employing conventional sol–gel method. X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FE-SEM), Mössbauer spectroscopy (MS) and vibrating sample magnetometer (VSM) analysis were carried out in order to characterize the structural and magnetic properties of particles. The XRD results confirmed the formation of single phase of spinel ferrite particles for a whole series of samples. The results of FTIR analysis indicated that the functional groups of Ni–Zn spinel ferrite were formed during the sol–gel process. Furthermore, FE-SEM micrographs revealed that the distribution of particles size is narrow. According to Mössbauer spectra,the doped cations are replaced in iron site occupancy of octahedral sites. It was found that with an increase in substitution contents magnetization decreased due to occupation of Al and Cr cations at low level substitutions in octahedral sites.  相似文献   

7.
《Ceramics International》2022,48(15):21187-21193
To obtain comprehensive materials with both high temperature coefficient of resistivity (TCR) and magnetoresistance (MR) at low magnetic fields, polycrystalline La0.72Ca0.28Mn1?xCrxO3 (x = 0, 0.02, 0.04, 0.06) ceramics were prepared herein by sol–gel method. Electronic configuration of Cr3+ ions is similar to that of Mn4+ ions, therefore, successive substitution of Mn with Cr increases electrical resistivity and decreases metal–insulator transition temperature of ceramics, even yielding hump-like feature for Cr-rich (x = 0.06) samples. The best TCR (28.50%·K?1) and MR (72.37%) values were obtained simultaneously at Cr dopant content of 0.02 (La0.72Ca0.28Mn0.98Cr0.02O3). Strong response of the material to temperature and magnetic field was caused by minimal symmetry of orthorhombic structure and the most robust Jahn–Teller distortion. With increasing Cr content, Mn3+/Mn4+ or Mn3+/Cr3+ double exchange was diluted, and Cr3+/Cr3+ or Cr3+/Mn4+ superexchange was promoted. However, the internal competition effect was not conducive to the improvement of material properties.  相似文献   

8.
《Ceramics International》2023,49(13):21577-21586
Multicomponent co-doping is an effective method to balance the counteracting magnetic properties of ferrite ceramics. In this work, novel (Ni,Cr,Zr)-co-doped M-type barium hexaferrites (BaFe12-3xNixCrxZrxO19, x = 0–0.8) were designed and synthesized by traditional solid-state reaction. Thermogravimetric analysis indicated that NiO would participate in the formation of secondary phase NiFe2O4 in the as-synthesized powder. Through traditional solid-state sintering, by using the synthesized pure-phase magnetic powders, almost full-dense ceramics were fabricated. Visual high-temperature deformation analysis revealed that there was no obvious difference in the sintering behavior and densification temperature of the ceramics with different compositional x, due to the low sintering activity of the as-synthesized magnetic powders. And X-ray diffraction analysis indicated that all the fabricated ceramics are of pure-phase M-type barium ferrite, and the lattice parameter c/a firstly increased as x raised up to 0.4 and then remained almost unchanged with further increased x, even if the lattice distortion became heavier. Microstructure examination revealed that the grain size monotonously decreased as the quantity of the substituent ions increased. The remnant magnetization and coercivity of the fabricated ceramics decreased monotonously as x increased, while the saturated magnetization could be maintained till the samples with x ≤ 0.4. Taking all the parameters into consideration, the samples with x = 0.4 might be a good candidate for transformer cores.  相似文献   

9.
《Ceramics International》2022,48(10):14060-14066
The vacancy defects, optical and magnetic properties of GdCr1-xTixO3 (0≤x ≤ 0.05) polycrystalline samples were investigated in this research. The crystal structural analyses show that the orthorhombic perovskite structure exists in all the samples. The positron annihilation spectra reveal that the vacancy defects and local electron density vary with the change of Ti ions valence states. The magnetic measurements show that the antiferromagnetic transition is shifted to lower temperature with the replacement of Ti ions in Cr sites, and the value of spin reorientation caused by the exchange interaction between Gd3+ ion and Cr3+ ion can be influenced by the change of Ti ions valence states, which rises from x = 0 to 0.04 and then decreases at x = 0.05 sample. Simultaneously, the optical band gap decreases from 2.7 eV to 0.8 eV with the introduction of Ti ions into the lattice, the result can provide a reference for improving optical activity of rare-earth chromium oxides.  相似文献   

10.
《Ceramics International》2020,46(5):6141-6145
The single phase Bi0.95Sm0.05Fe1-xNbxO3 (0 ≤ x ≤ 0.1) nanoparticles were synthesized by the sol-gel route, and the effect of Nb substitution on their magnetic, ferroelectric and photocatalytic properties were studied. X-ray diffractometry confirms a phase transformation from rhombohedral to orthorhombic with an increase in Nb substitution. The grain size decreases significantly, and the morphology of grains becomes homogeneous with the increase of Nb concentration. The maximum remnant magnetization (0.014 emu/g), coercivity (565 Oe) and polarization (0.592 μC/cm2) are observed in Bi0.95Sm0.05Fe0.9Nb0.1O3. It has been observed that the energy band gap has been slightly reduced from 2.14 to 2.03 eV with Nb substitution, indicating an improvement of photocatalytic activity. The methylene blue degradation is used to represent the photocatalytic ability of Bi0.95Sm0.05Fe1-xNbxO3 nanoparticles. The highest degradation efficiency (~74%) of methylene blue is obtained in Bi0.95Sm0.05Fe0.93Nb0.07O3, which is much higher than that of Bi0.95Sm0.05FeO3 (~51%) and can be attributed to the optimum particle size and the smallest energy band gap.  相似文献   

11.
《Ceramics International》2019,45(10):12949-12956
La-incorporated TiO2 nanoparticles (Ti1-xLaxO2) were synthesized by a sol-gel method followed by vacuum annealing at 500 °C for 4 h, and were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman scattering spectroscopy, and vibrating sample magnetometer (VSM), respectively. The results indicated that La ions were incorporated with TiO2 without distorting the tetragonal anatase structure, and a small amount of La ions were doped into TiO2 lattice by substituting the surface Ti sites, whereas most of the La atoms evenly distribute into TiO2 matrix in the form of La2O3. The incorporation of La ions with TiO2 matrix modulates the concentration of surface oxygen vacancy in Ti1-xLaxO2 nanoparticles. The room temperature ferromagnetism (RTFM) in Ti1-xLaxO2 nanoparticles varies with the concentration of surface oxygen vacancy due to ferromagnetic coupling interactions between singly ionized oxygen vacancy, thus RTFM can be tailored by modulating the concentration of surface oxygen vacancy via La ions incorporating.  相似文献   

12.
《Ceramics International》2021,47(24):34891-34898
Cr-doped zinc-lanthanum nanoferrites Zn1-xCrxLa0.1Fe1.9O4 (x = 0.09, 0.18, 0.27, and 0.36) were successfully synthesized using sonochemical reactors. Effect of powder production parameters were extensively studied and powder characterization was performed. Existence of cubic spinel structures in the prepared nanoferrites with the average crystallite size ranging from 35 to 51 nm was confirmed by X-ray diffraction studies. An electrochemical impedance analyzer was used to measure the dielectric constant (ε′), loss tangent (tan δ), and complex dielectric constant (ε") with respect to frequency and composition ratio. Maxwell–Wagner polarization and hopping mechanism were calculated to distinguish the variations in ε′, tan δ, and ε". The Nyquist impedance plots for nanoferrites revealed the pseudocapacitance as well as resistive behavior. Vibrating sample magnetometer studies reveled the ferromagnetic behavior of nanoferrites. Substantially increased saturation magnetization and decreased coercivity were noted with respect to increased Cr2+ ions in the prepared nanoferrites. It was found that the addition of chromium in Zn1-xCrxLa0.1Fe1.9O4 nanoferrites enhances the optical, electrical, and magnetic properties of the nanoferrites.  相似文献   

13.
《Ceramics International》2019,45(14):17157-17162
The (S, N) co-doped Ba2In2-xCrxO5+y (0 ≤ x ≤ 0.5) oxides are successfully obtained by mixing the Ba2In2-xCrxO5+y oxides and thiourea through a simple ball milling method followed by sintering at 400 °C for 3 h. The colors of the compounds change from orange-brown to yellow-green after reacting with thiourea. When Cr amount is small (x = 0.1), the crystal structure of (S, N) co-doped Ba2In2-xCrxO5+y is orthorhombic Ba2In2O5 phase. When x ≥ 0.3, the crystal structure of the sample is cubic BaInO2.5 phase. And this phase transition is the same as Ba2In2-xCrxO5+y. XPS results reveal that Cr6+ in Ba2In2-xCrxO5+y (0 ≤ x ≤ 0.5) oxides are reduced to Cr3+ after sintering. S exists in both cation and anion forms, and N exists in substitutional forms. UV–Vis analysis indicates that the yellow-green hue comes from the d-d transition of Cr3+, and the doping of S, N ions leads to a red shift of the absorption edge of the samples.  相似文献   

14.
《Ceramics International》2016,42(11):13238-13241
Sr-substituted NiZn ferrite nanopowders, Ni0.5-xZn0.5SrxFe2.0O4 (0≤x≤0.20), were synthesized by the sol-gel auto-combustion method. The effects of Sr substitution on the structural and magnetic properties have been investigated. Differential thermal analysis-thermogravimetry (DTA-TG), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM) measurements were used to characterize chemical, structural and magnetic properties. The DTA-TG results indicate that there are three steps of combustion process. XRD results indicate that the lattice parameter increases, and the average crystallite size decreases with increasing Sr substitution. The Sr2FeO4 and SrFe12O19 impurity phases formed with excess Sr substitution. The saturation magnetization monotonically decreases with the increase of Sr substitution. Meanwhile, the coercivity initially decreases with the increase of Sr substitution when x≤0.15, and increases when x>0.15.  相似文献   

15.
《Ceramics International》2022,48(3):3417-3425
Zn-doped nickel ferrite nanoparticles (ZnxNi(1-x)Fe2O4) were synthesized using the co-precipitation technique. The structural and compositional studies of the ZnxNi(1-x)Fe2O4 nanoparticles revealed their face-centred cubic spinel structure and an appropriate amount of Zn doping in nickel ferrite nanoparticles, respectively. The morphological analysis had been carried out to obtain the particle size of the synthesized nanoparticles. The magnetic studies revealed the superparamagnetic nature of the ZnxNi(1-x)Fe2O4 nanoparticles, and the maximum magnetization of 30 emu/g for the Zn0.2N0.8Fe2O4 sample. The M ? H curves were fitted with the Langevin function to obtain the magnetic particle diameter of ZnxNi(1-x)Fe2O4 nanoparticles. The electrical conduction in ZnxNi(1-x)Fe2O4 nanoparticles was explained through the Verway hopping mechanism. The Zn0.2N0.8Fe2O4 nanoparticle exhibited a higher electrical conductivity of 42 μS/cm and surface charge of ?29/7 mV due to the enhanced hopping of Fe3+ ions in the octahedral sites. Owing to this nature, they were identified as the suitable candidates in the applications such as thermoelectrics, hyperthermia, magnetic coating and for the preparation of conducting ferrofluids.  相似文献   

16.
The Cr3+ ions doped multi-oxide ZnFe2−xCrxO4 ferrite nanoparticles have been synthesized by chemical co-precipitation method. Site occupancies of Zn2+, Cr3+ and Fe3+ ions were analyzed using X-ray diffraction data and Buerger's method. The effect of the constituent phase variation on the magnetic hysteresis behavior was examined by saturation magnetization which decreases with the increase in Cr3+ content in place of Fe3+ ions at octahedral B-site. Typical blocking temperature (TB) around 90 K was observed by zero field cooling and field cooling magnetization study. Room temperature Mössbauer spectra show two paramagnetic doublets (tetrahedral and octahedral sites). The isomer shifts of both doublets decrease whereas quadrupole splitting and relative area of tetrahedral A-site increases with increasing Cr3+ substitution. The dielectric constant (measured on compositions x=0, 0.4, 0.8 and 1.0) increases when the temperature increases as in the semiconductor. This behavior is attributed to the hopping of electrons between Fe2+ and Fe3+ ions with a thermal activation.  相似文献   

17.
《Ceramics International》2016,42(9):10808-10812
The structural, magnetic, and dielectric properties of the Y1−xHoxFe0.5Cr0.5O3 (x=0, 0.05, 0.1, 0.3, and 0.5) compounds have been investigated. Rietveld refinement of the XRD patterns shows that the compounds possess orthorhombic perovskite structure. The dual magnetization reversal is observed in the samples with x=0.05 and 0.1, and it vanishes when x≥0.3. Ferromagnetic-like behavior with large coercive fields is observed in all Ho3+ doped YFe0.5Cr0.5O3 samples, indicating a doping induced metamagnetic behavior. This abnormal magnetization behavior can be explained by the antiparallel magnetic coupling between the Ho3+ and the canted Cr3+/Fe3+ moments, as well as the Ho–O–Ho magnetic interaction. The dielectric behavior in the frequency range from 100 Hz to 10 MHz is investigated. The low doped samples (x=0, 0.05, and 0.1) exhibit relaxation-like dielectric behavior and colossal dielectric constant in a wide temperature and frequency range. The dual magnetization reversal under low magnetic field makes these materials attractive candidates for the magnetic dual sensor devices.  相似文献   

18.
《Ceramics International》2015,41(7):8665-8669
Multiferroic ceramics Bi0.8Ba0.2Fe1−xCrxO3 (x=0, 0.05 and 0.1) were synthesized by using the conventional solid state reaction method. The pure phase with rhombohedral structure was confirmed by the X-ray diffraction measurements for all samples. It was shown that the magnetic and the ferroelectric properties were simultaneously improved, and the maximum values of the remnant magnetization (2Mr) and the remnant polarization (2Pr) at room temperature for all samples are around 1 emu/g and 1.9 μC/cm2, respectively. Furthermore, the leakage current density, the low frequency dispersion in the dielectric constant and the dielectric loss decreased with increasing the Cr concentration from x=0 to 0.1. A remarkable change in the P–E loop was observed whether a bias dc magnetic field was applied or not, approving the existence of the magnetoelectric coupling indirectly therein.  相似文献   

19.
Carbon dioxide reforming of methane was investigated over LaNi1?x Cr x O3 perovskite catalysts which were prepared by the malic acid method. The respective perovskite catalysts were a single phase of perovskite oxide without impurity phases. Their reduction behavior was characterized by temperature programmed reduction. In the LaNi1?x Cr x O3 perovskite catalysts, the catalytic activities were closely related to the reduction behavior of the catalysts, and the partial substitution of Cr to the B-site of perovskite catalysts promoted stability against reduction. When the x values were lower than 0.4, the LaNi1?x Cr x O3 perovskite catalysts were decomposed to La2O3 and Ni and the decomposition of perovskite structure led to large coke deposition. When the x values were higher than 0.4, the LaNi1?x Cr x O3 perovskite catalysts showed reduced catalytic activity but became stable to reduction and coke formation in the reforming reaction.  相似文献   

20.
Ceramic compacts in the systems Al2O3–Y2O3, Cr2O3–Y2O3 and Y3(CryAl1-y)5O12 (Cr-doped YAG) were prepared by solid state reaction in calcined co-precipitated powder mixtures of appropriate compositions. Various solid-solution phases were formed, e.g. Y3(Al1-xCrx)5O12, YAlyCr1-yO3 and Al2-xCrxO3. Composite materials in the pseudo-binary or ternary systems Al2O3–Y3Al5O12, Cr2O3–Y2O3 and Y3(Al1–xCrx)5O12–YAlyCr1–yO3–(AlzCr1−z)2O3 were obtained by hot-pressing appropriate powder precursors at 1600–1650°C for 1 h. The microstructure of the prepared materials was studied in a scanning electron microscope with element analysis facilities. X-ray diffraction was used to reveal the phases present and their lattice parameters. The chemical compatibility of these phases was investigated. The results are discussed with a special emphasis on the solubility of Cr in the YAG structure, and on the compatibility relationship between Cr-doped YAG and its neighbouring phases. A gel-coating process for preparing Al2O3–YAG composites with tailored microstructures is also described.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号