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

Use of high temperature X-ray diffraction and pair distribution function for the study of carbonation characteristics of Barium Titanate at nanoscale

Barium titanate (BT) is extensively used in electronic industries for its high dielectric constant. However, the dielectric properties of BT significantly change due to carbonation at nanoscale. Commercially available tetragonal BT powder was milled to study the local atomic distribution and phase transformation behaviour with temperature. Nano BT powder was prepared by the high energy ball milling (90 h) from its bulk counterpart. It was carbonated when it was exposed to open atmosphere. The milled BT sample was characterised by high temperature X-ray diffraction (HT-XRD), pair distribution function (PDF) and transmission electron microscope (TEM). Local atomic distribution was obtained from PDF analysis. The peak due to C-O and Ba-C pair distance were observed from PDF for 90 h milled carbonated BT. TEM analysis revealed that particle diameter was in the range of 15-50 nm. How the phase of nano BT ceramics transformed with temperature was strudied. It was observed that orthorhombic BT transformed into tetragonal and cubic phase via the monoclinic phase during heating at 900 degrees C. Coexistence of multi phases of BT was also observed from HT-XRD. BaCO3 disappeared at high temperature

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

Ambient formation of high pressure Ag2Si2O5 and non-stoichiometric Ag0.3Al0.7 alloy under confinement

We report results of Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive Analysis of X-rays (EDAX), X-ray Photoelectron Spectroscopy (XPS), X-ray Reflectivity (XRR), and X-ray Diffraction (XRD) and residual stress measurement studies of Ag-silica composite films on Al(001) co-deposited from precursors and spin-coated at different frequencies under ambient conditions. FESEM and EDAX show Ag nanoparticle formation, and XRD, XPS, and XRR show Ag0.3Al0.7 alloy and Ag-rich silicate Ag2Si2O5 formation in all samples. The alloy is non-stoichiometric and non-equilibrium, while the silicate forms at high oxygen pressure. XRR shows the presence of three layers, nanoparticles on top, silicate in the middle, and alloy at the bottom, on an Ag-doped Al substrate. Film thickness decreases exponentially with frequency. Individual layers increase in crystal domain size with a frequency of 3000 rpm when the silicate layer thins below unit cell thickness and the growth has a two-dimensional preference. Our results suggest total confinement by film thinning and local confinement from the Ag nanolayer. Residual stress measurements on the films deposited at 500 and 5000 rpms show a gradual increase in the tensile stress. The increase in spinning frequency reveals the formation of high pressure ambience

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

Study of short range structure of amorphous Silica from PDF using Ag radiation in laboratory XRD system, RAMAN and NEXAFS

At present synchrotron and neutron sources are the preferred choices for the Pair Distribution Function (PDF) analysis, but there is a need to explore PDF in a laboratory XRD system for quick feedback about the short range structure of the amorphous materials. Present work considered both crystalline (quartz) and amorphous silica to study the structural differences in silica by PDF analysis using Ag radiations in laboratory XRD. The structural information about short range ordering of the oxygen (O) atoms around silicon (Si) atoms as obtained by the PDF were compared with the results as obtained by Near Edge X-ray Absorption Fine Structure (NEXAFS) and RAMAN experiments. The PDF studies showed that the amorphous silica possessed short range periodicity within the basic unit of (SiO4)4− tetrahedra with a Si-O & O-O distance are of about 1.622 Å and 2.713 Å while the short range as well as long range ordered structure present in quartz with Si-O & O-O distance are 1.562 Å and 2.661 Å respectively. Raman spectra showed some asymmetry in amorphous silica which corresponds to the defects present in the lattice and thus forming the n-fold ring structure with Si and O resulting in the wide variation of bridging bond angle Si-O-Si in amorphous silica. NEXAFS studies revealed the structure of amorphous silica and quartz in the intermediate range (3–5 Å) at the Si L and O K edges. The structural information about short range ordering of the O around Si atoms as obtained by these methods were found to be in good match with the results as obtained by PDF, suggesting this technique may be used as a screening tool for routine PDF studies of amorphous materials

Study of short range structure of amorphous Silica from PDF using Ag radiation in laboratory XRD system, RAMAN and NEXAFS

At present synchrotron and neutron sources are the preferred choices for the Pair Distribution Function (PDF) analysis, but there is a need to explore PDF in a laboratory XRD system for quick feedback about the short range structure of the amorphous materials. Present work considered both crystalline (quartz) and amorphous silica to study the structural differences in silica by PDF analysis using Ag radiations in laboratory XRD. The structural information about short range ordering of the oxygen (0) atoms around silicon (Si) atoms as obtained by the PDF were compared with the results as obtained by Near Edge X-ray Absorption Fine Structure (NEXAFS) and RAMAN experiments. The PDF studies showed that the amorphous silica possessed short range periodicity within the basic unit of (SiO4)(4-) tetrahedra with a Si-O & O-O distance are of about 1.622 angstrom and 2.713 angstrom while the short range as well as long range ordered structure present in quartz with Si-O &O-O distance are 1.562 angstrom and 2.661 angstrom respectively. Raman spectra showed some asymmetry in amorphous silica which corresponds to the defects present in the lattice and thus forming the n-fold ring structure with Si and O resulting in the wide variation of bridging bond angle Si-O-Si in amorphous silica. NEXAFS studies revealed the structure of amorphous silica and quartz in the intermediate range (3-5 angstrom) at the Si L and O K edges. The structural information about short range ordering of the O around Si atoms as obtained by these methods were found to be in good match with the results as obtained by PDF, suggesting this technique may be used as a screening tool for routine PDF studies of amorphous materials

Progress on the BL2 beam measurement of the neutron lifetime

A precise value of the neutron lifetime is important in several areas of physics, including determinations of the quark-mixing matrix element |Vud|, related tests of the Standard Model, and predictions of light element abundances in Big Bang Nucleosynthesis models. We report the progress on a new measurement of the neutron lifetime utilizing the cold neutron beam technique. Several experimental improvements in both neutron and proton counting that have been developed over the last decade are presented. This new effort should yield a final uncertainty on the lifetime of 1 s with an improved understanding of the systematic effects