Study of Short-range Ordering in Amorphous and Nanocrystalline Materials from Laboratory based Pair Distribution Function (LPDF)

Determination of local atomic structure at nanoscale for both amorphous and nanocrystalline materials is very difficult and challenging. Local arrangement of atoms needs to be studied for understanding the local or short-range structural information. Pair distribution function (PDF) analysis is a technique used to study the short-range structure of the materials based on local atomic arrangement of atoms using synchrotron and neutron sources. But there is a demand for routine analysis based on laboratory X-ray diffractometer (XRD) using Ag radiation (lambda=0.5608 angstrom) with maximum achievableQvalue of 22 angstrom(-1). An attempt has been taken to study the short-range structure in crystalline Ni, silica glass (SiO2) and nano silica using total scattering experiment to show the capabilities and usefulness of PDF technique in laboratory XRD and are compared with the data from synchrotron radiation to achieve good quality scattering data and optimizing technical feasibility of the optics. PDF results of Ni showed the goodness of optical alignment. The first Si-O distance for both silica samples signified that they hold short- range order within the tetrahedral unit while differences are observed at higher radial distances. Laboratory based PDF experiment helped to get local/short- range structural information for better understanding the multifunctional properties of nano and disordered materials

Structure Solution of Glass and Ceramics using High Energy X-ray Diffraction Techniques

This article summarizes the possibilities and the application of the high energy X-ray diffraction methods to study the short range structures in the glass and nano-structured ceramic materials based on the recent developments and the instrumental facilities. The difficulties and the inapplicability of the conventional X-ray diffraction techniques to get structuralinformation about the glass and nano-structured materials over the past few decades has been resolved with the development of advanced X-ray based techniques both inhouse and synchrotrons. Some of the examples are discussed with the applicability of the high energy X-ray diffraction techniques to solve the structural problems of glass and nano-structured ceramics materials

Study of Short-range Ordering in Amorphous and Nanocrystalline Materials from Laboratory based Pair Distribution Function (LPDF)

Determination of local atomic structure at nanoscale for both amorphous and nanocrystalline materials is very difficult and challenging. Local arrangement of atoms needs to be studied for understanding the local or short-range structural information. Pair distribution function (PDF) analysis is a technique used to study the short-range structure of the materials based on local atomic arrangement of atoms using synchrotron and neutron sources. But there is a demand for routine analysis based on laboratory X-ray diffractometer (XRD) using Ag radiation (λ=0.5608 Å) with maximum achievable Q value of 22 Å$^{–1}$. An attempt has been taken to study the short-range structure in crystalline Ni, silica glass (SiO$_2$) and nano silica using total scattering experiment to show the capabilities and usefulness of PDF technique in laboratory XRD and are compared with the data from synchrotron radiation to achieve good quality scattering data and optimizing technical feasibility of the optics. PDF results of Ni showed the goodness of optical alignment. The first Si-O distance for both silica samples signified that they hold short- range order within the tetrahedral unit while differences are observed at higher radial distances. Laboratory based PDF experiment helped to get local/short- range structural information for better understanding the multifunctional properties of nano and disordered materials

Laboratory X-ray diffractometer for PDF experiments using Ag radiation

The conventional crystallographic structure solution by X-ray Diffraction technique using Rietveld method prove its great potential for determination of the average structure of the materials for long range periodicity. Experimentally, the structural information of long range periodic atomic ordering of material is reflected in the Bragg’s peaks while local or short rangestructure is reflected in the diffuse peaks. In order to obtain structural information about both average and local atomic structures, need a technique that will consider both Braggs peaks as well as diffuse peaks. Therefore, Total Scattering Atomic Pair Distribution Function (PDF) technique based on Debye Scattering function will be the only possible solution. Atpresent synchrotron and neutron sources are the choice for PDF analysis for short range structure study. But there is a need for routine analysis of such type of samples in a conventional laboratory XRD system to get the quick feedback about the short range structure. PDF analysis can be performed in a Laboratory X-ray diffractometer using Ag radiation (λ =0.5608 Å) to obtain maximum Q value i.e. 22 Å-1. The present work will report PDF based methodology in a laboratory XRD system to extract structural information about nanostructured and disordered materials over short and long range for structural characterization of crystalline and amorphous materials.Present work will report how this PDF technique used to unravel the structure of disordered materials and nanomaterials like amorphous silica, Ni, nano Ba-based Perovskite, etc for better understanding the materials at nano level. Structural information as obtained by the PDF analysis will help to control the performance of the disordered materials for tailoring thematerials at nano scale. This method may be applicable to the characterization of the nanoscale crystalline and amorphous materials based on PDF analysis in Laboratory XRD system using Ag Radiation. This proposed experimental technique will help to quick feedback about local or disordered structure based on PDF using Ag radiation in a laboratory XRD system

Sintering and characterization of a hard-to-hard configured composite: Spark plasma sintered WC reinforced alpha-SiAlON

In this study, a composite comprising WC particulate-reinforced alpha-SiAlON was fabricated by spark plasma sintering (1750 degrees C/40 MPa/25 min) in order to develop a hard-to-hard phase configuration and to toughen the hard matrix through particulate reinforcement. Irrespective of the composition, the sintered samples were almost theoretically dense. The nature of the overall sintering process for the composite appeared to be guided by the liquid phase sintering of the SiAlON phase. Microstructural analyses using scanning and transmission electron microscopy indicated the presence of both equiaxed and elongated alpha-SiAlON grains. The WC grains principally appeared equiaxed in nature. A reaction product was not observed at the WC/alpha-SiAlON interface. High-angle annular dark-field scanning transmission electron microscopy imaging indicated the reasonable distribution of the elements within the constituent grains and grain boundary. The presence of an intergranular glassy phase was confirmed, which was principally rich in oxygen and yttrium, with some occasional tungsten in the case of triple junctions. The composite exhibited an acceptable combination of flexural strength, hardness, and fracture toughness with values around 489 MPa, 20 GPa, and 6 MPa-m(0.5), respectively. In contrast to expectations, a decline in hardness was observed up to <= 30 wt% WC. Presumably, the WC grains acted as defects/inclusions with similar dimensions, which eventually resulted in inadequate interfacial performance and reduced hardness. Improvements in the Vickers hardness and fracture toughness were obtained at a WC loading of 40 wt%. The indentation size effect and load dependence of the fracture toughness were also determined for some selected specimens. Higher damage rates for the beta-Si3N4 counterbody against the 40 wt% WC/alpha-SiAlON composite were observed up to 30 N under unlubricated conditions compared with those obtained against the monolithic constituent phases, i.e., alpha-SiAlON and WC. The formation of an adherent tribolayer was observed

Effect of quenching and partitioning on the microstructure and mechanical properties of a medium carbon low alloy low silicon (0.3C-1.0Mn-0.4Si-0.6Cr-0.46Ni-0.26Mo) steel

The importance of advanced high strength steel having high strength with balanced ductility has led to immense researches all over the world for increasing the strength to weight ratio in different structural applications. The results of quenching and partitioning (QP) heat treatment process on a hot rolled advanced medium carbon steel (0.3C-1.0Mn-0.4Si-0.6Cr-0.46Ni-0.26Mo) have been analyzed in the present investigation. Hardness, tensile and yield strength of the steel show considerable improvement after the heat treatment process. Microstructural analyses by Optical, Scanning and Transmission Electron Microscopes show the creation of smaller units and sub-units of multiple phases containing martensite, retained austenite and bainite in the QP steel than those of as-received steel. Microstructure evolution was assessed by conducting the heat treatment with different isothermal partitioning times followed by x-ray Diffraction phase analyses. Austenite content has been found to increase with the duration of partition. Mechanical properties were related with the microstructures obtained at different stages of partitioning. Formation of thin retained austenite films in the periphery of individual bainite and martensite strips, blocks of austenite and the presence of overall small microstructural features have been proposed to be the reason for the improvement in hardness, tensile and yield strength and ductility of the as received hot rolled steel after the designed quench and partitioning treatment

Quantitative Strain and Compositional Studies of InxGa1-xAs Epilayer in a GaAs-based pHEMT Device Structure by TEM Techniques

In GaAs-based pseudomorphic high-electron mobility transistor device structures, strain and composition of the InxGa1 (-) As-x channel layer are very important as they influence the electronic properties of these devices. In this context, transmission electron microscopy techniques such as (002) dark-field imaging, high-resolution transmission electron microscopy (HRTEM) imaging, scanning transmission electron microscopy-high angle annular dark field (STEM-HAADF) imaging and selected area diffraction, are useful. A quantitative comparative study using these techniques is relevant for assessing the merits and limitations of the respective techniques. In this article, we have investigated strain and composition of the InxGa1 (-) As-x layer with the mentioned techniques and compared the results. The HRTEM images were investigated with strain state analysis. The indium content in this layer was quantified by HAADF imaging and correlated with STEM simulations. The studies showed that the InxGa1 (-) As-x channel layer was pseudomorphically grown leading to tetragonal strain along the 001] growth direction and that the average indium content (x) in the epilayer is similar to 0.12. We found consistency in the results obtained using various methods of analysis

AlN-SWCNT Metacomposites Having Tunable Negative Permittivity in Radio and Microwave Frequencies

Discovery of plasmon resonance and negative permittivity in carbon allotropes at much lower frequencies than those of metals has evoked interest to develop random metacomposites by suitable means of addition of these dispersoids in an overall dielectric matrix. Random metacomposites have always the advantage for their easy preparation techniques over those of their regular arrayed artificial counterpart. However, thermal management during the heat generation by electromagnetic attenuation in metamaterials is not yet studied well. The present communication discusses the dielectric permittivities and loss parameters of aluminum nitride-single-wall carbon nanotube (AlN-SWCNT) composites considering high thermal conductivities of both materials. The composites are dense and have been prepared by a standard powder technological method using hot pressing at 1850 degrees C under a nitrogen atmosphere. Increase in the negative permittivity value with SWCNT concentration (1, 3, and 6 vol %) in the composites had been observed at low frequencies. Characterization of the materials with Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and microstructure analysis by scanning and transmission electron microscopy (TEM) revealed the survivability of the SWCNTs and the nature of the matrix-filler interface. Plasmonic resonance following Drude's law could be observed at much lower plasma frequencies than that of pure SWCNT and for very little SWCNT addition. Exhibition of the negative permittivity has been explained with relation to the microstructure of the composites observed from field emission scanning electron micrographs (FESEM), TEM images, and the equivalent circuit model. High energy conversion efficiency is expected in these composites due to the possession of dual functionalities like high thermal conductivity as well as high negative permittivity, which should ensure the application of these materials in wave filter, cloaking device, supercapacitors, and wireless communication