In recent era, Alloy 617M remains as a promising material for high temperature application specially for components of advanced ultra-super critical (AUSC) power plant. Those components are exposed to mechanical and thermal loads (static and cyclic). Therefore, those are susceptible to fatigue, fracture and creep failures. In this paper, Alloy 617M is investigated for elastic-plastic fracture up to test temperature of 750 degrees C and thermal ageing up to 10,000 h. The specimens are prepared at 710 degrees C ageing temperature with different ageing conditions. Tensile, hardness and fracture tests are conducted to obtain tensile, hardness and fracture properties. Variations of mechanical properties and fracture toughness (JIC and J-Delta a curve) are observed with different ageing times and test temperatures. Abaqus finite element (FE) platform is used to simulate crack growth and to investigate the variations of crack tip constraint and plastic zone with ageing times and test temperatures. The variations in fracture behavior with ageing time as observed in experiments have been explained in terms of precipitation morphology in the microstructure.

In recent years, various materials have been developed to reduce the reliance of industries on indium, a primary component of transparent conducting oxides (TCOs), currently used for several optoelectronic devices. The search for indium-free TCOs calls for new materials, and perovskite oxides such as strontium vanadates, niobates, and molybdates offer good prospects. These perovskites are strongly correlated metals exhibiting high intrinsic electrical conductivity but, at the same time, have a good transparency. In this work, focus is placed on strontium niobate (SrNbO3) thin films and manipulate their optical conductivity by Ti substitution which shifts the plasma frequency and reduces electronic correlations. This allows achieving a low resistance of SrNb1-xTixO3 (x = 0-0.5) thin films while maintaining a high transparency in the visible light spectrum. An optimal figure-of-merit (FOM) of 10.3 (10-3 ohm-1) is obtained for x = 0.3. This FOM is comparable and possibly outperforms the optoelectronic capabilities of epitaxial Tin-doped Indium oxide (ITO) and several other proposed transparent conductor materials. The research paves a way for designing the next generation of transparent conductors, guided by insights from density-functional theory (DFT) and dynamical mean-field theory (DMFT).

The discovery of strontium niobate (SNO) as a potentially new transparent electrode has generated much interest due to its implications in various optoelectronic devices. Pristine SNO exhibits exceptionally low resistivity (∼10−4 Ω cm) at room temperature. However, this low resistivity occurs due to large number of carrier concentration in the system, which significantly affects its optical transparency (∼40%) in the visible range and hinders its practical applications as a transparent electrode. Here, we show that modulating the growth kinetics via oxygen manipulation is a feasible approach to achieve the desired optoelectronic properties. In particular, epitaxial (001) SNO thin films are grown on (001) lanthanum aluminate by pulsed laser deposition at different oxygen partial pressures and are shown to improve the optical transparency from 40% to 72% (λ = 550 nm) at a marginal cost of electrical resistivity from 2.8 to 8.1 × 10−4 Ω cm. These changes are directly linked with the multi-valence Nb-states, as evidenced by x-ray photoelectron spectroscopy. Furthermore, the defect-engineered SNO films exhibit multiple electronic phases that include pure metallic, coexisting metal-semiconducting-like, and pure semiconducting-like phases as evidenced by low-temperature electrical transport measurements. The intriguing metal-semiconducting coexisting phase is thoroughly analyzed using both perpendicular and angle-dependent magnetoresistance measurements, further supported by a density functional theory-based first-principles study and the observed feature is explained by the quantum correction to the conductivity. Overall, this study shows an exciting avenue for altering the optical and transport properties of SNO epitaxial thin films for their practical use as a next-generation transparent electrode.

The amount of energy that can be absorbed by armor steel during dynamic loadings, such as a crash, impact, or blast, is crucial. To characterize the behaviour of material deformation under such loading, rigorous testing and a suitable material model are needed. Within the scope of this research, relevant tensile tests in the dynamic range are carried out to obtain the parameters necessary for three different material models, namely, the Johnson-Cook (J-C), Rusinek and Klepaczko (R-K), and a newly proposed modified Johnson-Cook (MJ-C) model. Tensile tests are simulated using these three material models, and the results are compared with the experimental results. The Charpy impact test at five different striking velocities, viz. 3, 4, 5, 6, and 8 ms(-1) are numerically simulated using these material models. Upon comparing the obtained results with the experimental data, it becomes evident that the J-C model with modification (MJ-C) exhibits the best fit in prediction with regard to the specimen energy absorption and force versus displacement. A fractography investigation is also carried out to estimate the number of voids and void size with striking velocities. It shows that at higher strain rates, the number of voids increases. Additionally, the plastic deformation is restricted at high strain rates, leading to higher stress and reduced ductility.

This paper studies the dynamic and elevated temperature behavior of rolled homogeneous armor steel, which is crucial for applications such as blast, impact, crash, and ballistic resistance. The deformation behavior is analyzed through tensile tests. The tensile tests of RHA steel are conducted at quasi-static (〖10〗^(-4) s^(-1)≤(ε_p ) ̇≤〖10〗^(-1) s^(-1) ) to dynamic (〖10〗^(-1) s^(-1)≤(ε_p ) ̇≤36.439 s^(-1) ) strain-rates and at high temperatures ranging from room temperature (RT,27℃) to 500℃. Phenomenological Johnson-Cook (JC) models and semi-physical Rusinek-Klepaczko (RK) material models are employed in finite element (FE) simulations of tensile tests. The JC failure model, with a small modification, is used along with the material models to simulate the loss of load-bearing capacity of the component. All necessary material parameters are extracted from the test data. The material models and the damage model are integrated into ABAQUS CAE FE software through a user-defined material subroutine (UMAT). The simulated outcomes acquired from diverse material models are validated with relevant experimental findings, and the effectiveness of each material model is evaluated through qualitative and quantitative assessments. Observations reveal limitations in the existing models to accurately replicate material behavior under tension, particularly in the dynamic strain rate, and elevated temperature range. Consequently, a modified version of the JC model (MJC) is explored to better account for the impact of temperature on strain hardening and strain rate hardening. The proposed modification in the material model significantly enhances the predictive accuracy of FE simulations of tensile deformation across the entire spectrum of studied strain rates and temperatures compared to the original JC and RK models.

In this report, the optical properties of Ta doped SrTiO3 (STO) due to its potential in transparent conducting oxides (TCOs) is explored by a combination of theoretical studies based on density functional theory and spectroscopic ellipsometry. To achieve this theoretically, we vary the concentration of Ta from 0 - 12.5 effect on the resulting structural, chemical, electronic, chemical, and optical properties. Additionally, we perform band unfolding to shed light on the true nature of optical transitions due to Ta doping. We verify these results experimentally by fabricating epitaxial SrTi1-xTaxO3 thin films ( x = 0 - 5 by pulsed laser deposition and obtain the optical dielectric properties of the system with the help of spectroscopic ellipsometry. By combining theoretical and experimental studies, we provide evidence that the band gap of STO increases due to Ta doping while also enhancing its electronic properties. The findings of our study offer an extensive understanding of the intricacies associated with elemental doping in perovskite oxides and propose strategies for addressing obstacles associated with TCOs.

Oxide heterostructures have shown rich physics phenomena, particularly in the conjunction of exotic insulator-metal transition (IMT) at the interface between polar insulator LaAlO3 and non-polar insulator SrTiO3 (LaAlO3/SrTiO3). Polarization catastrophe model has suggested an electronic reconstruction yielding to metallicity at both the interface and surface. Another scenario is the occurrence of surface oxygen vacancy at LaAlO3 (surface-Ov), which has predicted surface-to-interface charge transfer yielding metallic interface but insulating surface. To clarify the origin of IMT, one should probe surface-Ov and the associated electronic structures at both the surface and the buried interface simultaneously. Here, using low-angle resonant soft X-ray scattering (LA-RSXS) supported with first-principles calculations, we reveal the co-existence of the surface-Ov state and the interface conducting state only in conducting LaAlO3/SrTiO3 (001) films. Interestingly, both the surface-Ov state and the interface conducting state are absent for the insulating film. As a function of Ov density, while the surface-Ov state is responsible for the IMT, the spatial charge distribution is found responsible for a transition from two-dimensional-like to three-dimensional-like conducting accompanied by spectral weight transfer, revealing the importance of electronic correlation. Our results show the importance of surface-Ov in determining interface properties and provides a new strategy in utilizing LA-RSXS to directly probe the surface and buried interface electronic properties in complex oxide heterostructures.

Stainless steels show a complicated material behavior involving viscoplasticity and Dynamic Strain Aging or DSA, wherein in certain loading conditions, the material exhibits negative strain rate sensitivity (SRS) while exhibiting positive SRS in others. Most conventional models used for modeling DSA lack either the accuracy or the ability to efficiently incorporate the temperature dependence or both. There are ANN and other machine learning-based model which are reported to predict the DSA stresses with reasonable accuracies for a wide range of loading conditions. However, they are not often implemented in an FE formulation. In fact, some authors concluded that at their present stages of ANN modelling, FE implementation remained a challenge. This creates a gap between models which can make reasonably accurate predictions and the models which are available for Finite Element (FE) implementation. The objective of the study was to focus on the application of ANN in modeling of DSA and implementation of the same in FE formulation. Here an ANN-based model was developed for 304 stainless steel. For this purpose, an ANN with two hidden layers was used. The ANN was trained by dropout method and produced better results than a single hidden layer model. The architecture of the ANN most suitable for the purpose was 3-10-10-1. The ANN-based model was implemented through a FE software. Results of the FE simulations show agreement with the experimental observations. Unlike most DSA models both conventional and ANN based, which are often limited by their application either at a specific temperature or in a small range of temperatures, the ANN model presented here, could predict the behavior of the material within and outside of the DSA regime.

Cubic SrTiO3 is widely used as a model perovskite oxide due to its exotic optical, electronic, magnetic, super-conducting, and ferroelectric properties, which are dominantly influenced by its lattice parameter. This paper reports on the experimental observation of Ta5+ dopant-induced expansion of the perpendicular lattice parameter (a perpendicular to) of (001) heteroepitaxial SrTixTa1-xO3 (x = 0-0.1) films grown at substrate temperature (Tg) of 750 degrees C under 5 x 10-5 mbar oxygen partial pressure (pO2). The experimental results demonstrate the synthesis of very high-quality epitaxial thin films in which almost all the Ta5+ dopants are substituted. However, not all the carriers are activated due to compensating defects. All these films have smooth surfaces and are stoichiometric in compositions. The value of a perpendicular to increases linearly with increasing Ta or free carrier concentrations. This expansion is modelled via density functional theory (DFT). The influences of three effects are considered in the present modelling: (i) ionic radius of Ta dopant (ii) deformation potential due to hydrostatic strain energy (iii) con-centration of free carrier. Further calculations of a perpendicular to are also performed by considering the influence of substrate and the results overestimate the experimental values by -1 %. Further experiments on other perovskite systems are required to establish the efficacy of these modelling approaches.

The amount of energy that can be absorbed by the armour steel during dynamic loading, such as a crash, impact, or blast, is of utmost importance. To characterise the behaviour of the material deformation under such loading, rigorous testing is required. The tensile test in dynamic range and the Charpy impact test are two examples of such dynamic loading. Within the scope of this research, tensile tests in dynamic range are carried out in order to obtain the parameters necessary for three different material models. The Charpy impact test was numerically simulated using thermo-viscoplastic material models, specifically the Johnson-Cook (J-C), Rusinek and Klepaczko (R-K), and a newly proposed modified Johnson-Cook (MJ-C) model. The simulation was performed at five different velocities viz. 3, 4, 5, 6 and 8 ms-1. Upon comparing the obtained results with the empirical data, it becomes evident that the MJ-C model exhibits the most accurate prediction among the three models with regard to the specimen energy absorption and force versus displacement. The fractography investigation was also carried out to estimate the number of voids and void size with striking velocities. It exhibits an increase in number of smaller size voids at higher strain rate. At high strain rate fracture the plastic deformation is restricted which results in higher hardness and less ductility.

The paper proposes an analysis of the characteristics of a cylindrical nanowire field effect transistor for two channel materials, namely Si and GaAs.The performance curves of Si and GaAs nanowire MOSFETs (GAA-NW-MOSFETs) in the 20 nm region are investigated via structure simulator called ATLAS.The simulation results show that the Si device has a much better threshold voltage and subthreshold swing, but the GaAs device has the best ION/IOFF current ratio and less drain-induced barrier-lowering (DIBL).Furthermore, performance characteristics of analog devices such as drain current, transconductance, as well as output conductance, subthreshold slope (SS) and threshold voltage of the device are compared for two different materials (Si and GaAs).It is found that the GaAs material provides reduced drive current and lower leakage current, giving a high ION/IOFF.In terms of SS, the Si material in the device ensures the perfect and stable device performance.

Alteration of transport properties of any material, especially metal oxides, by doping suitable impurities is not straightforward as it may introduce multiple defects like oxygen vacancies (Vo) in the system. It plays a decisive role in controlling the resistive switching (RS) performance of metal oxide-based memory devices. Therefore, a judicious choice of dopants and their atomic concentrations is crucial for achieving an optimum Vo configuration. Here, we show that the rational designing of RS memory devices with cationic dopants (Ta), in particular, Au/Ti1-xTaxO2-δ/Pt devices, is promising for the upcoming non-volatile memory technology. Indeed, a current window of ∼104 is realized at an ultralow voltage as low as 0.25 V with significant retention (∼104 s) and endurance (∼105 cycles) of the device by considering 1.11 at % Ta doping. The obtained device parameters are compared with those in the available literature to establish its excellent performance. Furthermore, using detailed experimental analyses and density functional theory (DFT)-based first-principles calculations, we comprehend that the meticulous presence of Vo configurations and the columnar-like dendritic structures is crucial for achieving ultralow-voltage bipolar RS characteristics. In fact, the dopant-mediated Vo interactions are found to be responsible for the enhancement in local current conduction, as evidenced from the DFT-simulated electron localization function plots, and these, in turn, augment the device performance. Overall, the present study on cationic-dopant-controlled defect engineering could pave a neoteric direction for future energy-efficient oxide memristors.

Dynamic strain ageing or DSA is exhibited by ferrous and aluminium alloys typically at elevated temperatures and low strain rates. This effect, in association with viscoplasticity, produces a complex material behaviour which is manifested through positive strain rate sensitivity of the flow stress in certain pockets of temperatures and strain rates and negative strain rate sensitivity in others. The conventional material models of DSA either lack the ability to accurately capture the DSA effect or to incorporate the effect of the temperature variation. The objective of this work was to propose a constitutive model which can do both. The desired material model was proposed by performing necessary augmentations to a conventional material model. The suitable conventional model for this purpose was identified through rigorous comparison of the existing models. The proposed constitutive model could accurately capture the DSA behaviour of austenitic stainless steel 304 for different strain rates over a range of temperatures across the peak DSA temperatures.

In recent times, the metal induced crystallization (MIC) process in amorphous semiconductors (a-Si and a-Ge) has been extensively investigated by many researchers due to potential applications of crystalline semiconductors in high-density data storage devices, flat panel displays, and high performance solar cells. In this context, we have presented a review on different schemes of MIC in metal/a-Si and metal/a-Ge bilayer films (with stacking change) on various substrates under different annealing conditions. The parameters, which limit crystallization of a-Si and a-Ge have been analyzed and discussed extensively keeping in mind their applications in solar cells and flat panel displays. The MIC of a-Si and a-Ge films under ion beam irradiation has also been discussed in detail. At the end, some suggestions to overcome the limitations of the MIC process in producing better crystalline semiconductors have been proposed. We believe that this review article will inspire readers to perform a thorough investigation on various aspects of MIC for further development of high efficiency solar cells and high quality flat panel displays.

Poly-crystalline Si film is an important material for its applications in microelectronics and solar cells. In order to realize poly-crystalline Si for practical application with high performance, it needs to be fabricated at room temperature. In this paper, we present a novel technique to develop poly-crystalline Si thin films at room temperature using 500 keV Xe+ ion irradiation. Here, the Al-induced crystallization process is employed to reduce the crystallization temperature. For that, c-Al (50 nm)/a-Si (150 nm) bilayer thin films have been used for ion irradiation experiments. Structural studies show that crystallization of Si starts at a threshold fluence of 3 × 1015 ions cm−2, and crystallinity is found to increase with increasing ion fluence. The results are explained in terms of displacement spike and thermal spike due to the interaction of energetic ions with target atoms. The transport of ions in matter Monte Carlo computer simulation code has been used to estimate the number of displacements due to ion irradiation. Generation of a sufficient amount of free Si atoms at threshold fluence and diffusion of these free Si atoms along the Al grain boundary starts the nucleation process.

One of the methods for describing the phenomenon of stable crack growth in ductile materials is the estimation of critical fracture energy, G(fr) as proposed by Marie and Chapuliot. These methods of calculation of G(fr) are applicable for large crack growth. However, the method for estimating G(fr) was re-investigated for short crack growth. It was observed in the previous works that the G(fr) values obtained for short crack growth gradually increases and saturates to the value at large crack growth. This saturated G(fr) value can be claimed to be a material property. It was also shown that a correction factor (function of critical CTOD and crack growth) when introduced to this saturated value of Gfr helps in obtaining the unsaturated values of G(fr). In the present work, an attempt is made to estimate G(fr) using the above mentioned re-investigated idea at the upper part of ductile to brittle transition temperature regime (0 degrees C to-60 degrees C). At sub-zero temperatures stable crack growth is much less when compared to the room temperature. The correction factor which is a function of saturated G(fr) value, CTOD and crack growth is found to be suitable for the CT specimen results even at low temperature. The values of unsaturated G(fr) values thus obtained using the correction factor are then used to simulate load versus load line displacement curves. The simulated load versus load line displacement curves at different temperatures are in good agreement with the experimental results irrespective of change in a/W ratios of the CT specimen.

Crystalline Si films incorporated with Al are important for applications in microelectronics and solar cells. In this paper, we report on the morphology of crystalline Si surfaces in Al/amorphous-Si bilayer thin films under ion beam irradiation at 100 °C. Micro-Raman and transmission electron microscopy studies show that best crystallization is achieved at a fluence of 1 × 1012 ions cm−2. The contact angle of Si surfaces (after chemically etched unreacted Al), referred to as absorber surfaces, decreases with increasing ion fluence. These surfaces are hydrophobic in nature and the hydrophobicity decreases with increasing ion fluence. Fractal and multifractal analysis of atomic force microscopy images, along with system energy/unit cell and Laplace pressure calculations, supports our observations. Moreover, the calculated multiple scattering cross sections of light, along with reflectivity measurements, indicate that absorber surfaces of best crystalline films have the lowest reflectivity. The present results suggest that such surfaces having low optical reflectance and a hydrophobic nature can be used as photon absorber layers for advanced solar cell devices.

We report experiments conducted in the field in the presence of fog, that were aimed at imaging under poor visibility. By means of intensity modulation at the source and two-dimensional quadrature lock-in detection by software at the receiver, a significant enhancement of the contrast-to-noise ratio was achieved in the imaging of beacons over hectometric distances. Further by illuminating the field of view with a modulated source, the technique helped reveal objects that were earlier obscured due to multiple scattering of light. This method, thus, holds promise of aiding in various forms of navigation under poor visibility due to fog.

SrTiO3 is a wide bandgap cubic perovskite oxide and displays many exotic properties, i.e., transparent conductivity, photocatalysis, metallicity, ferroelectricity, superconductivity, colossal magnetoresistance, two-dimensional electron gas, etc., due to the manipulations of defect chemistry and constituent elements via impurity doping. This paper reports on the intricacy of the structural and optoelectronic properties of the epitaxially stabilized 5 at. % Ta-doped SrTiO3 (001) thin films on LaAlO3 (001) substrates by systematically varying the growth temperature and oxygen partial pressure during the pulsed laser deposition process. The influences of Ta dopant and growth parameters on the epitaxial quality of these layers are understood by determining the dopant location and its concentration in the SrTiO3 lattice. The complex relationships of optical and electronic properties on growth parameters, dopant concentration, and single crystal quality of the films are demonstrated. The observed low resistivity (∼5 × 10−3 Ω cm) and high optical transparency (∼85%–90%) of optimized Ta-doped SrTiO3 films offer it as an exciting material for next generation transparent optoelectronics.