Influence of the common varistor dopants (CoO, Cr2O3 and Nb2O5) on the structural properties of SnO2 ceramics

The influence of dopants commonly used in SnO₂ varistor ceramics, such as CoO, Cr₂O₃ or Nb₂O₅, on the structural properties of SnO₂ was investigated. Several SnO₂-based ceramics containing only one of the dopants were prepared and characterized. Spectroscopic investigations [visible, near infrared (IR) and IR region] were performed to obtain information about dopants valence states inside the ceramics, as well as about their influence on electronic structure of the material. Structural properties were investigated by X-ray diffraction analysis and mechanisms of dopant incorporation were proposed. Obtained results were confirmed with results of the electrical measurements. Microstructural changes in doped ceramics were investigated by scanning electron microscopy (SEM) analysis that showed great differences in densities, grain size, and morphology of the SnO₂ ceramics depending on type of dopants and their distribution.     

Effect of l-alanine,Mn(II) and glycine dopants on the structural,crystalline perfection,second harmonic generation (SHG), dielectric and mechanical properties of BTCA single crystals

Bis thiourea cadmium acetate (BTCA) single crystals were grown at room temperature with different dopants by aqueous solution technique. The crystal system of the grown crystals with all the dopants was confirmed by powder X-ray diffraction study which confirms that there is no extra phase due to doping of l-alanine (LA), Mn(II) and glycine (Gly). It was further confirmed by FT-IR as well as FT–Raman spectroscopy analysis. The effect of LA, Mn(II) and Gly doping on the crystalline perfection was assessed by high-resolution X-ray diffractometry (HRXRD) analysis which revealed that the grown crystals with Gly doping are more perfect in comparison of other dopants. The SHG efficiency was measured using the Kurtz powder technique and shows that the grown crystals with Gly doping are more efficient in comparison of other dopants which is in tune with crystalline perfection. The low values of dielectric constant and loss also revealed that the grown crystals are defect free. The hardness values were found to be increased by increasing the doping concentration.     

Identification of ultradilute dopants in ceramics

The properties of ceramic materials are strongly influenced by the presence of ultradilute impurities (dopants). Near-edge X-ray absorption fine structure (NEXAFS) measurements using third-generation synchotron sources can be used to identify ultradilute dopants, provided that a good theoretical tool is available to interpret the spectra. Here, we use NEXAFS analysis and first-principles calculations to study the local environments of Ga dopants at levels of 10 p.p.m in otherwise high-purity MgO. This analysis suggests that the extra charge associated with substitutional Ga on a Mg site is compensated by the formation of a Mg vacancy. This defect model is then confirmed by positron lifetime measurements and plane-wave pseudopotential calculations. This powerful combination of techniques should provide a general method of identifying the defect states of ultradilute dopants in ceramics.     

多组元掺杂石墨微观结构及其性能的研究

制备了Si,Ti比组元和Si,Ti,B4C三组元掺杂石墨材料并研究了其结构和性能,实验结果表明,与相同条件下制得的纯石墨材料相比,掺杂石墨材料具有高密度,高强度以及极低的电阻率等特点,双组元掺杂石墨的导电性略优于三组元掺杂石墨,但其机械强度却明显低于后者,分析表明,各组元在材料中所起的作用各不相同,钛,硼添加剂对材料的机械强度有增强作用,对材料的石经具有催化作用,少量硅的添加有利于石墨材料的石墨化和蔼以及导电性能的提高,但含量较多时,由于Si的大量逸失导致气率增大,使掺杂石墨的导电极性及机械性能降低。     

Production and characterization of pure and Cr<Superscript>3+</Superscript>-doped hydroxyapatite for biomedical applications as fluorescent probes

Pure and Cr³⁺-doped hydroxyapatite (HAP) were prepared via chemical precipitation route. The XRD measurements revealed that the typical HAP powder pattern was obtained. SEM analysis indicated that aggregates of nanoparticles were formed. EDX analysis indicates that the [Ca]/[P] concentration ratio was higher than the expected values but can be explained by the presence of carbonate groups as dopants. The optical absorption spectra of the doped samples presented absorption bands typical of Cr³⁺ occupying to different crystalline sites. From the position of the bands, it was possible to estimate the crystal field parameters for both sites of Cr³⁺ in the HAP matrix. The emission spectra of the Cr-doped samples were also investigated and typical transitions of the dopant ion, in trivalent state, were identified. The potential use of the Cr³⁺-HAP as fluorescent probes for medical applications was discussed.     

Structural, magnetic and optical studies of (Zn0.90Co0.05Ni0.05O) DMS

ZnO DMS were prepared by co-precipitation method. Single phase Zn_0.90Co_0.05Ni_0.05O was confirmed by powder X-ray diffraction (XRD). The samples were characterized by EDS to confirm the expected stoichiometry. SEM revealed no surface precipitation of dopants. Photoluminescence for pure ZnO was observed in the bluish green region. Compared to undoped ZnO, the luminescence of Co-Ni co-doped ZnO was strongly quenched. The samples were examined for its magnetic property using vibrating sample magnetometer (VSM) which indicated ferromagnetic behavior at room temperature with a coercivity of 123.37 g. XRD measurements showed impurity phase for samples prepared by ceramic method.     

TiO2 doped with nitrogen: synthesis and characterization

In this study, nitrogen-doped titanium dioxide (TiO2) powders were synthesized in two ways: by heating of titanium hydroxide with urea and by direct hydrolysis of titanium tetraisopropoxide (TTIP) with ammonium hydroxide. The samples were characterized by structural (XRD), analytical (XPS), optical (UV/Vis absorption/reflection and Raman spectroscopy) and morphological (SEM, TEM) techniques. The characterization suggested that the doped materials have anatase crystalline form without any detectable peaks that correspond to dopants. The absorption threshold of titanium dioxide was moved in the visible range of optical spectrum from 3.2 eV to 2.20 eV. Particle sizes of synthesized powders were obtained from XRD measurements and from TEM data ranging from 6-20 nm. XPS and Raman spectroscopy were used for detection of nitrogen in doped samples.     

掺杂对PMS-PZ-PT三元系材料微结构和电性能的影响

探讨了Nb2O5、NiO、Fe2O3掺杂量对三元系PMS—PZ—PT陶瓷的微观结构和电性能的影响。实验结果表明：随着掺杂量的增加，有一个共同的规律：物相组成由四方相向三方相转变；掺杂物在PMS—PZ—PT材料准同型相界区的固溶度比较小；适当的少量掺杂使εr、d33、Kp3等都有所提高，所不同的是，少量硬性掺杂和取代能提高Qm，而软性掺杂材料的Qm值却随着掺杂量的增加一直下降，改性后的组分具有良好的压电性能，能更好的满足超声马达实际使用的要求。     

Preparation and characterization of niobates. Part VI: Synthesis, XRD, SEM and piezoelectric studies of potassium and barium-doped lead strontium niobates

Lead niobates belong to orthorhombic symmetry and acquire tetragonal symmetry at 570°C. Some lead-based ceramic compounds have been synthesized and their structural and ferroelectric properties studied. Strontium, barium and potassium were used to reduce the transition temperature and to control the grain growth, thereby electrical properties. The transition temperature was found to decrease from 465°C to 282°C with dopants. The transition temperature was drastically reduced with the addition of barium. This can be attributed to the suitability of doping ion in determining the transition temperature and other piezoelectric constants. Powder X-ray diffraction studies were carried out and orthorhombic symmetry was confirmed. The lattice constants were calculated through diffraction patterns. The average grain size was measured from the scanning electron microscopy (SEM) pictures taken on fractured surfaces of the samples.     

Hydrothermal derived nanostructure rare earth (Er,Yb)-doped ZnO: structural,optical and electrical properties

The structural, optical and electrical properties of undoped and rare-earth (Er, Yb) doped zinc oxide (ZnO) nanopowder samples synthesized by hydrothermal method were investigated. The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy. The optical properties of undoped and rare-earth (Er, Yb) doped ZnO were carried out with UV–visible diffuse reflectance spectroscopy techniques. XRD results reveal that Yb and Er doped ZnO nanopowders have single phase hexagonal (Wurtzite) structure without any impurities. SEM analysis indicate that dopants with different radii affected the surface morphology of ZnO nanostructures. The optical band gap of all samples were calculated from UV–Vis diffuse reflectance spectroscopy data. We have obtained band gap values of undoped, Er and Yb doped ZnO as 3.24, 3.23, 3.22 eV, respectively. Electrical characterization of the samples were made in the 280–350 K temperature range using Van der Pauw method based on Hall effect measurement. The carrier concentrations decreased for both Er and Yb doping while the Hall mobility and electrical resistivity increased with Yb, Er doping compared to undoped ZnO nanopowder at room temperature. The temperature dependent resistivity measurements of Er doped ZnO showed a metal–semiconductor transition at about 295 K, while Yb doped ZnO showed characteristic semiconductor behavior.     

Polypropylene-blended organoclay nanocomposites – preparation,characterisation and properties

Intercalated/exfoliated nanocomposites of thermoplastic polyolefin (TPO) blended nanoclay (Cloisite 20?A and Cloisite 30B) were fabricated using melt extrusion process. Polypropylene grafted maleic anhydride (PP-g-MA) was used as a compatibiliser to improve the dispersibility of clay. TPO/nanoclay composites were prepared with different percentages of clay loading (3, 5 and 7?wt%) by adding PP-g-MA as a compatibiliser. The nanocomposites having 5?wt%C20A/5?wt% compatibiliser exhibited a remarkable improvement in mechanical (tensile modulus, flexural modulus and impact strength) and thermal (heat distortion temperature, HDT) properties. The thermal measurements have been carried out by differential scanning calorimetry, thermogravimetric analysis and HDT methods. Dynamic mechanical analysis studies indicated that PP macromolecules were intercalated or exfoliated between the interlayer of silicates. The morphology of nanocomposites was characterised by scanning electron microscopy (SEM) and X-ray diffraction (XRD) was used to find out the arrangement of crystals in the nanocomposites. The SEM and XRD clearly demonstrated the progressive break up of particles and results in decreased particle size with the optimised combination.     

Galvanostatic deposition of Poly(N-methylpyrrole) film with various dopants and co-dopants: A comparative study

Synthesis of Poly(N-methylpyrrole) (P(NMP)) film with various dopants viz. PolyVinyl Sulphonic acid (PVS), p-Toluene Sulphonic acid (pTS), Sodium Nitrate (NaNO₃) has been studied by using galvanostatic deposition method. This is a comparative study of influence of above dopants on the synthesis of P(NMP) film using electrochemical studies, conductivity measurements, FTIR spectral studies and SEM. The optimal film growth was achieved for synthesis of the P(NMP) film in the presence of PVS. The influence of co-dopants i.e. PolyVinyl Sulphonic acid/ p-Toluene Sulphonic acid (PVS/pTS) and PolyVinyl Sulphonic acid/sodium nitrate (PVS/NaNO₃) on galvanostatic deposition of P(NMP) film has also been studied. This study reveals that the synthesized P(NMP) film with dopant PVS and co-dopant PVS/NaNO₃ provides good polymer matrix for immobilization of biocomponent.     

复合氧化物掺杂法制备抗还原BCTZ系陶瓷的研究

提出了一种制备抗还原BCTZ系陶瓷材料的新工艺. 采用溶胶-凝胶法在500～800℃下合成复合氧化物掺杂剂, 此掺杂剂与水热法合成的超细(Ba_1-xCa_x)(Ti_1-yZr_y)O₃粉体混合球磨可得抗还原介质瓷料, 该瓷料可在还原性气氛中烧成适用于贱金属电极的, 具有高介电常数和低介质损耗的多层陶瓷电容器陶瓷材料. 本文讨论了复合氧化物掺杂剂的合成温度、陶瓷烧结温度和退火时间等工艺参数对陶瓷介电性能和微结构的影响. 研究表明, 在低温下合成的纳米颗粒的复合氧化物掺杂剂(纳米掺杂剂)很适合超细瓷料的掺杂改性. 在500～800℃内, 复合氧化物掺杂剂的合成温度升高将导致BCTZ系陶瓷的居里点、介质损耗和介电常数最大值的降低.对陶瓷烧结工艺的研究表明, 采用此新工艺可获得符合Y5V标准的BCTZ系抗还原介质陶瓷, 其室温相对介电常数不小于18000, 介质损耗低于0.7%, 绝缘电阻率达到10¹²Ω·cm, 居里点在5～20℃之间可调, 平均晶粒尺寸G_AV小于4μm. 该新工艺可望用于大容量Y5V镍内电极多层陶瓷电容器的生产.     

Role of dopants in Bi-Sr-Ca-Cu-O system

The role of Al and Ag dopants in the nominal composition, 4336 of Bi-Sr-Ca-Cu oxide has been studied, using a new chemical phase analysis method known as differential dissolution besides XRD and resistivity and magnetic susceptibility measurements. Our investigation reveals that (a) it is relatively easy to realize high-T _c phase (2223) in both Al- and Ag-doped samples with the same nominal composition and heat treatment history (b) both samples consist of superconducting phases with more or less the same basic composition and equal amounts, (c) 2112 phase may be a superconductor and (d) superconducting properties with Al and Ag dopants are different.     

Growth and characterization of indium antimonide and gallium antimonide crystals

Indium antimonide and gallium antimonide were synthesized from the respective component elements using an indigenously fabricated synthesis unit. Bulk crystals of indium antimonide and gallium antimonide were grown using both the vertical and horizontal Bridgman techniques. Effect of ampoule shapes and diameters on the crystallinity and homogeneity was studied. The grown crystals were characterized using X-ray analysis, EDAX, chemical etching, Hall effect and conductivity measurements. In the case of gallium antimonide, effect of dopants (Te and In) on transport and photoluminescence properties was investigated.     

钛酸锶钡改性掺杂的研究进展

介绍了国内外近几年钛酸锶钡(Strontium Barium Titanate,BST)在掺杂改性方面的研究现状及各种掺杂对BST介电性能的影响,重点讨论了不等价掺杂及掺杂量对漏电流和介电损耗的影响,论述了材料组成、显微结构与介电性能之间的关系.最后提出了关于掺杂改性方面存在的问题.     

High performance PA6/CNTs nanohybrid fibers prepared in the melt

Commercial and home-made carbon nanotubes (CNTs) were plasma treated under oxygen atmosphere and then added to polyamide 6 (PA6) in order to prepare fibres by melt spinning. For comparison, pristine nanofillers were used too. The effect of functionalization and of filler characteristics on the morphological, rheological, mechanical and electrical properties of the fibres was studied by TEM and SEM, rheological measurements, tensile and electrical conductivity tests. The results demonstrated that the functionalization led to a better mechanical performance and the morphological analysis confirmed that the adhesion, the dispersion and the alignment of the nanotubes within the polymer matrix were improved when using functionalized CNTs. Electrical tests marked that functionalization slightly reduced the conductivity of the materials.     

Simultaneous doping of aluminum and fluorine on zinc oxide nanopowder using a low-cost soft chemical route

Simultaneous doping of aluminum (Al) and fluorine (F) on ZnO nanopowder was successfully achieved by a soft chemical method. The strong X-ray diffraction peaks revealed the high crystallinity of the synthesized nanopowder and the XRD profiles showed that the material has hexagonal wurtzite structure. EDAX results confirmed the presence of Al and F and from the quantitative analysis it was observed that there was a systematic increase in both dopants in the final product as they were included in the starting solution. The SEM images showed that the ZnO:Al:F powders have nanorod structure with hexagonal cross section. The simultaneous doping enhanced the carrier concentration of the ZnO nanopowders indicated by the higher IR reflectivity.     

Characterization of polypropylene–polyethylene blends made of waste materials with compatibilizer and nano-filler

Waste polypropylene and polyethylene were blended by a twin-screw extruder with two compatibilizers (PE-g-MAH and EPDM) and an additive (O-MMT). The mechanical properties were measured firstly. By adding O-MMT, the tensile strength showed a decline while the impact strength made a promotion. The phase morphology was observed by scanning electron microscopy (SEM) to explore the fracture toughness of blends. The blend with EPDM had a better compatibilization than PE-g-MAH. X-ray diffraction was used to investigate the crystallization behavior and the result showed no change by blending. Moreover, further measurements such as thermogravimetric (TGA) and differential scanning calorimetry (DSC) were taken to show the thermal stability and crystallization temperature of the blend. Additionally, the storage modulus and loss modulus are measured by dynamic mechanical analysis (DMA), the presence of O-MMT caused the increases of the storage modulus and loss modulus.     

Preparation and characterization of doped WO3 photocatalyst powders

WO₃ semiconductor particles, useful in solar energy conversion processes, were doped with transition metal ions, Ti(III), V(IV), Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Ru(III) by a high-temperature sintering technique. The method of preparation of these photocatalysts is described in detail. The structural changes effected during sintering were investigated by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The XRD analysis indicated that the monoclinic crystal structure of WO₃ was not altered during sintering. SEM studies showed that the sizes of the particles ranged from 1 to 10 μm and the crystallinity was increased due to doping. The dopants were found to be mostly distributed on the surface of WO₃ particles.