Structural,microstructural and magnetic properties of nanocomposite isotropic Sm(CobalFe0.1MyZr0.04B0.04)7.5 ribbons with M=Ni,Cu and y=0.09 and 0.12

In boron-substituted melt-spun Sm(Co,Fe,Cu,Zr)_7.5-type alloys a nanocomposite microstructure and high coercivities in both as-spun and short-time annealed ribbons can be obtained. In the present study three different compositions, namely Sm(Co_0.73Fe_0.1Cu_0.09Zr_0.04B_0.04)_7.5, Sm(Co_0.70Fe_0.1Cu_0.12Zr_0.04B_0.04)_7.5 and Sm(Co_0.70Fe_0.1Ni_0.12Zr_0.04B_0.04)_7.5 have been examined in order to investigate the influence of composition on the magnetic properties and the microstructure. Melt-spun ribbons have been obtained and annealing has been followed under argon atmosphere for 30–75 min at 600–870 °C. For the as-spun ribbons the TbCu₇-type of structure and fcc-Co as a secondary phase have been identified in the X-ray diffraction patterns. For the annealed ribbons above 700 °C the 1:7 phase transforms into 2:17 and 1:5 phases. The TEM studies have shown a homogeneous nanocrystalline microstructure with average grain size of 30–80 nm. Coercivity values of 15–27 kOe have been obtained from hysteresis loops traced in non-saturating fields. The coercivity decreases with temperature, but it is sufficiently large to maintain values higher than 5 kOe at 380 °C.     

Magnetic properties and grain-boundary structure transition of melt-spun (Sm0.12Co0.87Cu0.01)97(VC)3 under annealing

Effects of annealing treatment on the magnetic properties and microstructure of SmCo₇-based magnets doped with VC and Cu were investigated. The coercivity of the as-spun ribbons (Sm_0.12Co_0.87Cu_0.01)₉₇(VC)₃ was 3.6 kOe. It was increased to 7.3 kOe after annealing at 800 °C for 15 min. A fixed single 1:7H structure and regular 1:7H dendrite grains with long axes preferentially parallel to each other had been attained during rapid solidification and subsequent annealing treatment. However, TEM results revealed that there was grain-boundary phase rich in C and Cu besides 1:7H phase in the as-solidified ribbon. After annealing, the grain-boundary phase decomposed to Cu-, Sm- and C-rich intergranular phases. Cu-, Sm- and C-rich regions formed at the grain boundaries after annealing improved the coercivity of (Sm_0.12Co_0.87Cu_0.01)₉₇(VC)₃ by decreasing the magnetostatic interactions and act as effective domain wall pinning sites.     

High-temperature oxidation resistance and magnetic properties of Si-doped Sm2Co17-type magnets at 500 °C

The high-temperature oxidation resistance and magnetic properties of Si-doped Sm₂Co₁₇-type magnets at 500 °C were systematically investigated. The Sm(Co_0.76, Fe_0.1, Cu_0.1, Zr_0.04)₇Si_x (x=0–0.6) magnets were prepared by the conventional powder metallurgical technique. It is found that the addition of silicon in the Sm₂Co₁₇-type magnet can remarkably improve its oxidation resistance. Moreover, a small amount of silicon addition can also increase its high-temperature intrinsic coercivity. A maximum intrinsic coercivity of 6.7 kOe at 500 °C was obtained for the Sm₂Co₁₇-type magnet with Si content x=0.4, whose high-temperature maximum energy product loss was about 2.5 times smaller than pure Sm₂Co₁₇-type magnet after oxidation at 500 °C for 100 h, indicating the enhanced oxidation resistance. Its corresponding Curie temperature and saturation magnetization are about 723.9 °C and 7.4 kG, respectively.     

Studies on the preparation and ethanol gas sensing properties of spinel Zn0.6Mn0.4Fe2O4 nanomaterials

Zn_1−xMn_xFe₂O₄ (x = 0, 0.2 and 0.4) nanomaterials were synthesized by sol–gel citrate method and studied structural and gas sensing properties. The structural characteristics of synthesized nanomaterials were studied by X-ray diffraction measurement (XRD) and transmission electron microscope (TEM). The results revealed that the particle size is in the range of 30–35 nm for Mn–Zn ferrite with good crystallinity. The gas sensing properties were studied towards reducing gases like LPG, CH_4, CO and ethanol and it is observed that Mn–Zn ferrite shows high response to ethanol at relatively lower operating temperature. The Zn_0.6Mn_0.4Fe₂O₄ nanomaterial shows better sensitivity towards ethanol at an operating temperature 300 °C. Incorporation of 1.5 wt.% Pd improved the sensitivity, selectivity, response time and reduced the operating temperature from 300 °C to 230 °C for ethanol sensor. The response time of 200 ppm ethanol in air is about 10s.     

Magnetic properties of FexCo1−x/CoyFe1−yFe2O4 composite under hydrothermal condition

The metal–ferrite composites Fe_xCo_1−x/Co_yFe_1−yFe₂O₄ are synthesized by using disproportion of Fe (II) and reduction of Co (II) by Fe⁰ under hydrothermal condition. The size of the particles of the composites decreases as the [KOH] decreasing. The composites are measured by TEM and it can be deduced that when [KOH] = 0.1, the size of the alloy body-centered cubic (BCC) in composites is 20 ± 7 nm, the size of the Cobalt ferrite (spinel) is 170 ± 50 nm. The maximal value of the saturation magnetization (Ms) of the composite is about 100.14 emu/g, which is synthesized under Co (II)/Fe (II) = 0.05, [KOH] = 1 N, T = 150 °C and t = 3 h. The value of Hc of the composite synthesized under Co (II)/Fe (II) = 0.5, t = 3 h, T = 150 °C and [KOH] = 10.2 mol/L is about 2878.19 Oe. The Fe–Co alloy is synthesized through a reduction reaction of the composites in a flowing gaseous mixture. There is a maximal value (302.9 emu/g) of the Ms for the alloys generated at 1000 °C, which is the Co_0.412Fe_0.588 alloy.     

Transport properties and defect analysis of La1.9Sr0.1NiO4 + δ

The oxygen flux through La_1.9Sr_0.1NiO_4 + δ has been measured as a function of oxygen activity gradient and temperature (750–1000 °C). The oxygen nonstoichiometry was determined by thermogravimetry in the temperature range of 400–1000 °C and oxygen partial pressures of 0.0002–1 atm. The total conductivity was measured over a similar range of conditions. The oxide ion partial conductivity derived from the oxygen flux data is approximately 4 orders of magnitude lower than the total, mainly p-type electronic conductivity. The defect structure was derived based on the data. Combining the oxygen flux and oxygen nonstoichiometry, the self diffusion coefficient of oxygen interstitials was evaluated.     

Effect of heat treatment on structure, magnetization and magnetostriction of Fe81Ga19 melt-spun ribbons

Structure, magnetization and magnetostriction of melt-spun Fe₈₁Ga₁₉ ribbons were investigated both before and after heat treatment. The matrix of melt-spun Fe₈₁Ga₁₉ ribbons kept a body-centered-cubic (bcc) structure (A2) at room temperature. [1 0 0] preferred orientation was formed during melt-spinning process and became stronger with the increase of the ribbon thickness. For the ribbons with a thickness of 110 μm, maximum saturation magnetostrictive strain of −189 ppm along ribbon length was obtained in the samples heat treated at 800 °C for 3 h and then quenched into water. This value was about 16% larger than that of melt-spun ones, which could be contributed to the single disordered A2 structure and the enhancement of [1 0 0]-oriented texture. However, when the ribbon samples were cooled at 2 and 0.5 °C/min after heat treatment at 800 °C for 3 h, a minor quantity of ordered D0₃ and L1₂ phase was found to precipitate in the A2 matrix, respectively, which resulted in the reduction of both magnetization and magnetostrictive strain.     

Pyroelectric properties in three phases coexistence Pb[(Mn0.33Nb0.67)0.5(Mn0.33Sb0.67)0.5]0.08(ZrxTi1−x)0.92O3 lead ceramics

The bulk dense Pb[(Mn_0.33Nb_0.67)_0.5(Mn_0.33Sb_0.67)_0.5]_0.08(Zr_xTi_1−x)_0.92O₃ pyroelectric ceramics have been successfully prepared by the conventional solid method. The effect of three phases coexistence in the ceramics is studied. When x = 0.95 and 0.85 in the ceramics, the maximum pyroelectric coefficient peaks appear at 23 °C and 45 °C, and the maximum values are 26.5 × 10⁻⁴ C/m² °C and 25.5 × 10⁻⁴ C/m² °C, respectively. The maximum pyroelectric coefficient appears large while the peaks widths are small. When the two kinds of ceramic powders mixed with the mol ratio of 2:1, the pyroelectric coefficient of the ceramics is above 10.0 × 10⁻⁴ C/m² °C in a broad temperature range from 20 °C to 55 °C. The possible physical mechanism of the temperature broadened phenomenon is briefly discussed.     

Magnetic and magnetotransport properties of Co-doped manganites with perovskite structure

A systematic study of the doping of the Mn-sites by cobalt in three series of manganites — La_0.76Ba_0.24(Mn_1−xCo_x)O₃ single crystals, La_2/3Ba_1/3(Mn_1−xCo_x)O₃ and La(Mn_1−xCo_x)O₃ ceramics has been performed. It was found that La(Mn_1−xCo_x)O₃ annealed at 800°C in the range 0.4x0.9 is a mixture of ferromagnetic domains with ordered Mn and Co ions and ionically disordered spin-glass domains. In the quenched samples the fraction of spin-glass-type component increases strongly. The La_2/3Ba_1/3(Mn_1−xCo_x)O₃ solid solutions exhibit also an evidence for phase separation in the range 0.5x0.8. All the La(Mn_1−xCo_x)O₃ samples show an insulating behavior, however, magnetoresistance reduces strongly when the cobalt content rises to x=0.5. The La_0.76Ba_0.24(Mn_1−xCo_x)O₃ single crystals show first-order phase transition below their Curie points associated with a change of ground state of the Co²⁺ ions. The magnetic phase diagrams are depicted. The results are discussed in terms of positive Mn³⁺–O–Mn⁴⁺, Mn³⁺–O–Mn³⁺, Mn⁴⁺–O–Co²⁺ and negative Mn⁴⁺–O–Mn⁴⁺, Co²⁺–O–Co²⁺, Co²⁺–O–Mn³⁺ superexchange interactions as well as Co²⁺ and Mn⁴⁺ ionic ordering.     

Effect of annealing temperature on microstructure, optical and electrical properties of sputtered Ba0.9Sr0.1TiO3 thin films

Ba_0.9Sr_0.1TiO₃ (BST) thin films were deposited on fused quartz and Pt/TiN/Si₃N₄/Si substrates by radio frequency magnetron sputtering technique. Microstructure and chemical bonding states of the BST films annealed at 700 °C were characterized by field emission scanning electron microscopy, X-ray photoelectron spectroscopy, glancing angle X-ray diffraction and Raman spectrum. Optical constants including refractive indices, extinction coefficients and bandgap energies of the as-deposited BST film and the BST films annealed at 650, 700 and 750 °C, respectively, were determined from transmittance spectra by envelope method and Tauc relation. Dielectric constant and remnant polarization for the BST films increase with increasing annealing temperature. Leakage current density-applied voltage (J–V) data indicate that the dominant conduction mechanism for all the BST capacitors is the interface-controlled Schottky emission under the conditions of 14 V < V < 30 V and −30 V < V < −14 V. Furthermore, the inequipotential J–V characteristics for the BST films annealed at various temperatures are mainly attributed to the combined effects of the different thermal histories, relaxed stresses and strains, and varied Schottky barrier heights in the BST/Pt and Pt/BST interfaces.     

Morphology and magnetic properties of Co0.8Fe2.2O4 films prepared by the chemical solution deposition

Co_0.8Fe_2.2O₄ ferrite thin films have been prepared on Si(0 0 1) substrates by the chemical solution deposition. Structural characteristics indicate all films are single phase with spinel structure and the space group and the mean grain size increases from 8 to 30 nm with the increase of annealing temperature. The magnetic properties of Co_0.8Fe_2.2O₄ thin films are highly dependent on annealing temperature. The sample annealed at 800 °C possesses high saturation magnetization, moderate coercivity and squareness ratio, making it a promising application candidate in high-density record and magneto-optical materials.     

Y2(Fe1-x-y,Coy,Crx)17化合 物的结构及居里温度

通过x射线衍射及磁测量手段研究了Y₂(Fe_1-y-x,Co_y,C r_x)₁₇化合物的结 构及居里温度.研究结果表明Y₂(Fe_1-y-x,Co_y,Crx)₁₇化合物具有六 角相的Th₂Ni₁₇型结构.随着x的增加，Y₂(Fe 关键词： 2(Fe_1-y-x')" href="#">Y₂(Fe_1-y-x y')" href="#">Co_y x)_{1 7}化合物')" href="#">Cr_x)_{1 7}化合物 x射线衍射 居里温度     

Synthesis and magnetic properties of Sm–Y3Fe5O12 nanoparticles

Garnet nanoparticles Y_3−xSm_xFe₅O₁₂ were fabricated by a sol–gel method. The XRD patterns of all the samples have only peaks of the garnet structure and the sizes range from 34 to 67 nm. Results of VSM show that the saturation magnetization of Y_3−xSm_xFe₅O₁₂ (0<x3) decreases on increasing the Sm concentration x evidently. Meanwhile, it is observed that with the enhancement of the surface spin effects, the saturation magnetization rises as the nanoparticle size is increased.     

Synthesis, phase and microstructure characteristics of Pb(Zr0.52Ti0.48)O3–(Bi3.25La0.75)Ti3O12 ceramics

Ceramics with formula (1 − x)Pb(Zr_0.52Ti_0.48)O₃–x(Bi_3.25La_0.75)Ti₃O₁₂ (when x = 0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0) were prepared by a solid-state mixed-oxide method and sintered at temperatures between 950 °C and 1250 °C. It was found that the optimum sintering temperature was 1150 °C at which all the samples had densities at least 95% of theoretical values. Phase analysis using X-ray diffraction indicated the existence of BLT- as well as PZT-based solid solutions with corresponding lattice distortion. Scanning electron micrographs of ceramic surfaces showed a plate-like structure in BLT-rich phase while the typical grain structure was observed for PZT-rich phase. The grain sizes of both pure BLT and PZT ceramics were found to decrease as the relative amount of the other phase increased. This study suggested that tailoring of properties of this PZT–BLT system was possible especially on the BLT-rich side due to its large solubility limit.     

Lithium ion conductive glass–ceramics with Li3Fe2(PO4)3 and YAG laser-induced local crystallization in lithium iron phosphate glasses

The glasses with the composition of 37.5Li₂O–(25 − x)Fe₂O₃–xNb₂O₅–37.5P₂O₅ (mol%) (x = 5,10,15) are prepared, and it is found that the addition of Nb₂O₅ is effective for the glass formation in the lithium iron phosphate system. The glass–ceramics consisting of Nasicon-type Li₃Fe₂(PO₄)₃ crystals with an orthorhombic structure are developed through conventional crystallization in an electric furnace, showing electrical conductivities of 3 × 10^− 6 Scm^− 1 at room temperature and the activation energies of 0.48 eV (x = 5) and 0.51 eV (x = 10) for Li⁺ ion conduction in the temperature range of 30–200 °C. A continuous wave Nd:YAG laser (wavelength: 1064 nm) with powers of 0.14–0.30 W and a scanning speed of 10 μm/s is irradiated onto the surface of the glasses, and the formation of Li₃Fe₂(PO₄)₃ crystals is confirmed from XRD analyses and micro-Raman scattering spectra. The crystallization of the precursor glasses is considered as new route for the fabrication of Li₃Fe₂(PO₄)₃ crystals being candidates for use as electrolyte materials in lithium ion secondary batteries.     

Effect of annealing on magnetoimpedance of Co68Fe4Zr10Cu2B16 ribbons

Magnetoimpedance (MI) in Co₆₈Fe₄Zr₁₀Cu₂B₁₆ alloy has been investigated in the frequency range 500 kHz–5 MHz and with the application of external steady magnetic field in the longitudinal direction, up to 100 Oe. MI measurements were carried out on as-cast ribbons and also on conventionally annealed and Joule-annealed ribbons. In as cast ribbons, the maximum MI observed is 13% at a frequency of 500 kHz and it decreases to 5% and 4% with conventional annealing at 100 °C and 150 °C, respectively. On the other hand, MI decreases to 8% and 6% with Joule annealing employing currents of 100 mA and 200 mA, respectively. However, Joule annealing with the application of a magnetic field of 5–10 Oe in the transverse direction causes the MI to decrease to 12% and 11% for currents of 100 mA and 200 mA, respectively. In the as-cast ribbons, double peak behavior is observed in all the frequencies whereas, in the annealed ribbons, double peak behavior in general is observed only at high frequencies.     

Die-upset Nd11.5Fe72.4Co9Nb1B6.1 magnets with additions of Zn, Al and Sn

The magnetic properties and microstructure were studied for bulk Nd_11.5Fe_72.4Co₉Nb₁B_6.1 magnets synthesized by hot-pressing and subsequent die-upsetting the melt-spun ribbons with additions of three kinds of low-melting-point metal (Zn, Al and Sn). Die-upset Nd_11.5Fe_72.4Co₉Nb₁B_6.1 magnets have low magnetic properties since they have an inhomogeneous microstructure with many coarse grains. The microstructure of die-upset magnets remains almost unchanged with Al and Sn additions, which only have negative effects on the magnetic properties. Different from Al and Sn additions, Zn addition changes the phase composition of the starting melt-spun powers due to the reaction of Zn and Nd₂Fe₁₄B during hot-pressing and hot-deforming and enhances the development of the desired [0 0 1] texture and improves the microstructure of die-upset magnets. As a result, an anisotropic magnet with good maximum energy product (221 kJ/m³) and high coercivity (670 kA/m) is obtained by adding 2 wt% Zn to the Nd_11.5Fe_72.4Co₉Nb₁B_6.1 alloy.     

Emergence of order in nanocrystalline SmFe9

Three samples consistent with 1 : 12, 2 : 17 and 1 : 7 stoichiometry, ball-milled and subsequently annealed at temperature T_a between 600 and 1200°C were studied by Rietveld analysis, coupled to Curie temperature T_c measurements and Mössbauer spectroscopy. For all samples, at 600°CT_a<900°C, the detected out-of-equilibrium phase is the hexagonal P6/mmm structure derived from TbCu₇ with the composition SmFe₉. At T_a900°C the ordered phase of Th₂Zn₁₇-type is observed. With increasing T_a the unit cell parameter small variation of the parent SmFe₉ induces a decrease of T_c and H_hf. For T_a=600°C SmFe₉ is defined by a=0.4919 nm, c=0.4162 nm, T_c=207°C and H_hf=232 kOe. The resulting ordered Sm₂Fe₁₇ is characterized by nm, c=3×0.4147 nm, T_c=144°C and H_hf=219 kOe. For T_a=750°C the SmFe₉ T_c is 171°C associated to H_hf=222 kOe.     

Electrical characteristics and low-temperature sintering of BiFeO3-modified Pb(Zr,Ti)O3–Pb(Fe2/3W1/3)O3–Pb(Mn1/3Nb2/3)O3 ceramics with ZnO addition

Effects of ZnO addition on electrical properties and low-temperature sintering of BiFeO₃-modified Pb(Zr,Ti)O₃–Pb(Fe_2/3W_1/3)O₃–Pb(Mn_1/3Nb_2/3)O₃ were investigated. The investigations revealed that the sintering temperature can be decreased to 950 °C, and the favorable properties were obtained with 0.10 wt% ZnO added ceramics. The electrical properties were as follows: d₃₃ = 313 pC/N, K_p = 0.56, tan δ = 0.0053, ε_r = 1407 and T_c = 295 °C, which showed that this system was a promising material for the multilayer devices application.     

Effect of Y2O3 addition on the conductivity and elastic modulus of (CeO2)1 − x(YO1.5)x

The conductivity and elastic modulus of (CeO₂)_1 − x(YO_1.5)_x for x values of 0.10, 0.15, 0.20, 0.30, and 0.40 were investigated by experiments and molecular dynamics simulations. The calculated conductivity exhibited a maximum value at approximately 15 mol% Y₂O₃; this trend agreed with that of the experimental results. In order to clarify the reason for the occurrence of the maximum conductivity, the paths for the transfer of oxygen vacancies were counted. The numerical result revealed that as the content of Y₂O₃ dopant increases, the number of paths for the transfer of oxygen vacancies decreases, whereas the number of oxygen vacancies for conductivity increases. Thus, the trade-off between the increase in the number of vacancy sites and the decrease in the vacancy transfer was considered to be the reason for the maximum conductivity occurring at the Y₂O₃ dopant content of approximately 15 mol%. The calculated elastic modulus also exhibited a minimum value at approximately 20 mol% Y₂O₃, which also agreed with the experimental results. It was shown that the Y–O–Y bonding energy increased with the increasing content of Y₂O₃ dopant. Thus, the trade-off between the increase in the number of vacancy sites and that in the Y–O–Y bonding energy was considered to be the reason for the minimum elastic modulus occurring at the Y₂O₃ dopant content of approximately 20 mol%.