Effect of holmium on the magnetic and electrical properties of barium based W-type hexagonal ferrites

A series of BaHo_xFe_16−xO₂₇ (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) W-type hexagonal ferrites were prepared by co-precipitation technique at high annealing temperature of 1320 °C. XRD reveals single W-type hexagonal phase in these ferrites. The grain size is measured by SEM analysis using line intercept method. Saturation magnetization, retentivity and coercivity were measured from MH-loops taken on VSM. It was observed that magnetization increases with the increase of Ho content due to difference in ionic radii of Ho³⁺ (0.901 Å) and Fe³⁺ (0.67 Å) ions. Room temperature dc resistivity increases as a function of Ho³⁺ that may be due to separation between grains. The dc electrical resistivity decreases as a function of temperature which indicates the semi-conducting behavior of the samples.     

Preliminary Study on Electrical and Optical Properties of ZnO Film Grown by MOCVD

1 ＩｎｔｒｏｄｕｃｔｉｏｎＺｎＯｉｓａｗｉｄｅ ｇａｐ ( 3.2ｅＶａｔｒｏｏｍｔｅｍｐｅｒａｔｕｒｅ)ｓｅｍｉｃｏｎｄｕｃｔｏｒｍａｔｅｒｉａｌｈａｖｉｎｇｔｈｅｗｕｒｔｚｉｔｅｓｔｒｕｃｔｕｒｅｗｉｔｈｄｉｒｅｃｔｅｎｅｒｇｙｂａｎｄ .Ｉｔｈａｓｂｅｅｎｃｏｎｓｉｄｅｒｅｄａｓａｐｒｏｍｉｓ ｉｎｇｍａｔｅｒｉａｌｆｏｒｏｐｔｏｅｌｅｃｔｒｏｎｉｃｄｅｖｉｃｅｓｉｎｔｈｅｎｅａｒｕｌｔｒａｖｉｏｌｅｔ(ＵＶ)ａｎｄｂｌｕｅｓｐｅｃ ｔｒａ .ＡｎｉｎｔｅｒｅｓｔｉｎｇｆｅａｔｕｒｅｏｆＺｎＯｉｓｉｔｓｌ…     

Studies on thin film based flexible gold electrode arrays for resistivity imaging in electrical impedance tomography

Practical phantoms are essential to assess the electrical impedance tomography (EIT) systems for their validation, calibration and comparison purposes. Metal surface electrodes are generally used in practical phantoms which reduce the SNR of the boundary data due to their design and development errors. Novel flexible and biocompatible gold electrode arrays of high geometric precision are proposed to improve the boundary data quality in EIT. The flexible gold electrode arrays are developed on flexible FR4 sheets using thin film technology and practical gold electrode phantoms are developed with different configurations. Injecting a constant current to the phantom boundary the surface potentials are measured by a LabVIEW based data acquisition system and the resistivity images are reconstructed in EIDORS. Boundary data profile and the resistivity images obtained from the gold electrode phantoms are compared with identical phantoms developed with stainless steel electrodes. Surface profilometry, microscopy and the impedance spectroscopy show that the gold electrode arrays are smooth, geometrically precised and less resistive. Results show that the boundary data accuracy and image quality are improved with gold electrode arrays. Results show that the diametric resistivity plot (DRP), contrast to noise ratio (CNR), percentage of contrast recovery (PCR) and coefficient of contrast (COC) of reconstructed images are improved in gold electrode phantoms.     

碳纤维-石墨复合水泥基材料导电性能的试验研究

在石墨水泥基材料中掺入低电阻率且具有阻裂功能的短切碳纤维可以提高材料的导电性能.试验研究了环境温度、碳纤维长度及组合长度碳纤维等对石墨水泥基材料电阻率的影响.结果表明,碳纤维可以改善石墨水泥基材料的性能,组合长度碳纤维的掺入有利于材料导电网络的形成.     

Resistivity measurements on hydrogenation disproportionation desorption recombination phenomena in Nd---Fe---B alloys with Co, Ga and Zr additions

Resistivity measurements on the hydrogenation disproportionation desorption recombination (HDDR) phenomena in near stoichiometric Nd---Fe---B alloys were carried out in the temperature range of T=740–900 °C in order to investigate the effect of additional elements such as Co, Ga and Zr. These studies were combined with detailed temperature-pressure-analysis to relate the observed changes in resistivity with the solubility of hydrogen in the rare-earth metal. Higher relative resistivity changes can be observed when lower disproportionation temperatures are applied. This tendency depends on the amount of hydrogen absorbed in the disproportionated mixture. The addition of Co leads to a longer completion time of the disproportionation reaction. In particular, the alloy with both Co and Ga additions exhibits the longest completion time. These observations suggest that Co stabilises the 2-14-1 phase and Ga addition enhances this effect. These additional elements decrease the number of hydrogen atoms absorbed per formula unit and also increase the onset hydrogen pressure of the disproportionation and recombination reactions. On desorption, Co and Ga additions decrease the activation energy of the recombination reaction and lead to a higher reaction rate of these alloys compared to that of the ternary alloy, which is especially pronounced during the initial stages of recombination and which may be relevant for the development of anisotropic features in the recombined state.     

气体精炼对铝电阻率影响的研究

介绍了用Cl2,Ar,Ar-Cl2复合气体精炼对工业纯铝电阻率的影响,工艺合理可使电阻率下降0.5%～0.6%。对于含硼铝,用Ar-Cl2复合气体精炼,电阻率有所回升;而用Ar精炼,电阻率可降低0.2%～0.4%。     

Synthesis of the Bi-2222 Compounds of Bi–Sr–Ln(Zr)–Cu–O (Ln = Sm,Eu, Gd,and Dy)

Bi-based superconducting compounds with the 2222 structure has been already synthesized in the Bi₂Sr₂- (Ln_1−x Ce _x )₂Cu₂O_10+y (Ln = Sm, Eu, and Gd) systems. One of the characteristics of these compounds is the existence of the fluorite-like (Ln_1−x Ce _x )₂O₂ block between two CuO₅ pyramids in the crystal structure. The tetravalent ions of Ce⁴⁺ are reported to be necessary to stabilize the 2222 structure. Recently, we have discovered that the Bi-2222 phase could be composed in the Bi₂Sr₂(Ln_2−x Zr _x )Cu₂O _z (Ln = Sm, Eu, Gd, and Dy) systems, where Zr⁴⁺ is used as a new tetravalent ion stabilizing the 2222 structure in stead of Ce⁴⁺. In the new system, nearly single 2222 phase samples have been obtained at the nominal composition of x=0.5 (Ln = Sm, Eu, and Gd) and in the range of 0.1≤x≤0.3 (Ln = Dy). Among them, the sample with Ln = Gd has the smallest resistivity at 273 K. But it is a semiconductor, and the conduction process at low temperatures is assumed to be followed by a two-dimensional VRH. The experimental results for the Gd samples with a partial substitution of Pb for Bi in the Bi₂Sr₂(Gd_2−x Zr _x )Cu₂O _z system are also reported.     

Effect of Solidification Conditions on Structure and Properties of Rapidly-Solidified Sn-7.5wt%Sb Alloy

The effect of cooling speed on structure and properties of the rapidly-solidified Sn-7.5wt%Sb has been investigated. The samples in this study were prepared using a single roller melt spinning technique with two speeds: 15.7 and 30.7 m/s, respectively. The results showed formation of the intermetallic compound SnSb. This intermetallic compound changes in the amount which precipitated in the two samples. This behavior tends to affect the properties of these two samples. Also higher cooling speed tends to reduce the crystallite size, which in turn reduces the melting point of the resulting alloy compared to that of the lower cooling speed.     

Microstructure and thermoelectric properties of p-type Bi-Sb-Te-Se thin films prepared by electrodeposition method

P-type Bi-Sb-Te-Se thermoelectric thin films with thickness of 8 μm have been prepared by cathodic electrodeposition technique on Au substrate from nitric acid solution system at room temperature. Cyclic voltammetry was used for determination of the deposition potentials of the thin films. In order to enhance the crystallinity, as well as the thermoelectric properties of the deposited films, they were annealed at 523 K for 2 h under nitrogen atmospheric pressure condition. X-ray diffraction (XRD), environmental scanning electron microscopy, and energy-dispersive spectroscopy (EDS) were employed to characterize the thin films. Seebeck coefficients and resistivities of the films were also evaluated. The results revealed that Bi, Sb, Te and Se could be co-deposited to form Bi-Sb-Te-Se semiconductor compound in the solution containing Bi^III, Sb^III, Te^IV and Se^IV and the compositions of the films were sensitive to the electrodepositing potentials. The XRD results suggested that the crystal structure of the thin films were changed from amorphous state to polycrystalline after annealing. The EDS data indicated that the composition of the films was consistent with XRD results. The annealed Bi-Sb-Te-Se thin films exhibited the Seebeck coefficients of 116-133 μV/K and a maximum power factor of 0.62 mW·K^− 2·m^− 1.     

Structural,electrical and mechanical properties of selenium doped thallium based high-temperature superconductors

In this study, highly-refined chemical powders were synthesized by having them ready in appropriate stoichiometric proportions with conventional solid state reaction method so that they would produce the superconductor TlPb_0.3Sr₂Ca_1−xSe_xCu₂O_y (x = 0; 0.4; 0.6; 1.0). This study aims to understand effect of the selenium doping on the superconducting, structural and mechanical properties of the aforementioned superconducting material. The effect of the doping rates on the structural and electrical properties of the sample has been identified. Electrical characteristics of the TlPb_0.3Sr₂Ca_1−xSe_xCu₂O_y material were measured using standard four point probe method. Structural characteristics were examined with the powder X-ray diffractometer (XRD) and scanning electron microscope (SEM). Mechanical properties were analyzed with Vickers microhardness measurements on the sample surface. According to the results, it was observed that the reflection comes from the (00l) and parallel planes increased with Se doping. Particle size increases with increasing doping ratio. According to results of the mechanical measurements, all samples exhibit indentation size effect (ISE) behavior. Comparing the obtained results with theoretical studies, it was understood that Hays Kendall approach is the best method in determination of mechanical properties and analyzing microhardness of the materials.