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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 understan...

Sudden breakdown of 'toughened glass' (TG) without apparent causes have grave consequences. We present results of investigations on two samples - pieces of a TG door that broke down spontaneously (STG) and pieces of a TG sheet broken down intentionally (ITG). Both samples have same morphology and X-ray Diffraction showed the same structure for both samples indicating no major difference in microstructure. No trace of Ni or S could be observed from X-ray Fluorescence Spectroscopy whereas a small depletion in Na content was seen in STG, which became much more apparent from low angle X-ray Absorption Near-edge Spectroscopy at Na K-edge, pointing to a surface depletion. Positron Annihilation Spectroscopy studies indicated very large concentration of free volume cavities in STG, implying that the erosion of the structure and loss of rigidity is a result of atomic motions within the glass and the associated weakening of the molecular bonds. From Fourier Transform Infrared Spectroscopy, a reduction in the Si-O-Si bonds and an enhancement in the O-H bonds could be identified indicating a conversion of the former to Si(OH)_4. The bond distances of different pair of atoms were calculated from Atomic Pair Distribution Function experiments. An increase in total porosity especially in larger pores were observed in STG over ITG, from Twin Mercury Porosimetry. We propose a simple model in which the Si-O network is destabilized due to leaching out of Na-ions from STG over time, leading to accumulation of large pores, increase of overall porosity and final collapse of the structure.

Instances of sudden breakdown of ‘toughened glass’ (TG) without apparent causes have grave consequences. Here we present results of investigations on two types of samples – pieces of a TG door that broke down spontaneously (STG) and pieces of a TG sheet broken down intentionally (ITG). In both cases, the broken pieces have the same morphology and were studied through X-ray Diffraction (XRD), X-ray Fluorescence Spectroscopy (XRF), X-ray Absorption Near-edge Spectroscopy (XANES) at Na K-edge, Fourier Transform Infrared Spectroscopy (FTIR), Twin Mercury Porosimetry (TMP), Atomic Pair Distribution Function (PDF) and Positron Annihilation Spectroscopy (PAS). XRD and PAS showed the same structure and high defect concentration for both the samples indicating no major difference in microstructure due to aging in STG. No trace of Ni or S could be observed from XRF, casting doubt on the presence of NiS inclusions. PAS studies indicated very large concentration of free volume cavities in the STG sample, implying that mechanical instability leading to the erosion of the structure and loss of rigidity is a result of atomic motions within the glass and the associated weakening of the molecular bonds. From XRF, a small depletion in Na content was seen in STG, which became much more apparent from low angle XANES, pointing to a surface depletion. From FTIR, a reduction in the Si–O–Si bonds and an enhancement in the O–H bonds could be identified indicating a conversion of the former to Si(OH)4. The bond distances of different pair of atoms were calculated from atomic Pair Distribution Function experiments. An increase in total porosity especially in larger pores (diameter ≥100–200 µm, from TMP) were observed in STG over ITG. Based on these results, we propose a simple model in which the Si–O network is visualized as suffering from destabilization due to the leaching out of the Na-ions from the STG over time, leading to the accumulation of large pores, increase of overall porosity and the final collapse of the structure.

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.