The structural, mechanical, electronic and magnetic phase transitions in Mn-doped SiTiPd Half Heusler alloy(HhA), are investigated using first-principles DFT calculations, with Mn incorporated at either the Ti or Pd site. A strategic aim is to elucidate the role of correlation of Ti 3d electrons in stabilizing doping induced phase transitions. Both the doping compositions, SiTi1-xMnxPd (Dp1) and SiTiPd1-xMnx (Dp2), undergo similar structural transitions from cubic to orthorhombic, then trigonal, and revert back to cubic with full Mn substitution. In Dp1, these transitions are distinctly captured by Birch-Murnaghan equation of state analysis, whereas those in Dp2 remain elusive due to gradual and energetically shallow nature of the transition. Electronic structure calculations show that Dp1 evolves from a non-magnetic state to a ferrimagnetic half-metal with 100% spin polarization and a spin-down gap ranging from 0.74 to 0.78 eV up to a doping concentration of x = 0.625, followed by a transition to a metallic phase due to delocalization of Ti 3d electrons at higher doping. In contrast, Dp2 becomes metallic even at low doping, with weak spin polarization resulting from dominant p-d and d-d hybridization that suppresses correlation effects. Magnetic and mechanical analyses further reveal that Dp1 maintains stability across the entire doping range, while Dp2 becomes mechanically unstable under heavy doping. These results highlight the effectiveness of the doping strategy in Dp1 for realizing robust and tunable phase transitions in half heusler alloys, while also addressing a critical knowledge gap concerning correlation driven phenomena in transition metal based thermoelectric and spintronics materials.

To elucidate hidden electron correlation effects in Half Heusler alloys(HhAs), a systematic first-principles investigation is carried out on the XTiPd(X=Si, Ge, Sn, Pb) family using a hierarchy of theoretical approaches ranging from standard density functional theory(DFT) to DFT+U and fully dynamical DFT combined with dynamical mean field theory(DFT+DMFT). At the DFT level, all XTiPd compounds are identified as non-magnetic indirect band-gap semiconductors stabilized by crystal field splitting of Ti 3d states arising from s-p-d hybridization with Pd and X atoms. These materials further exhibit high Seebeck coefficients, moderate electrical and thermal conductivities, and consequently enhanced thermoelectric performance, indicating their stability for both n-type and p-type thermoelectric modules. Upon inclusion of on-site Coulomb interactions for Ti 3d electrons, a pronounced sequence of interaction-driven electronic and magnetic phase transitions emerges, evolving from a non-magnetic semiconductor to a spin polarized n-p sandwich semiconductor, followed by ferrimagnetic half-metallic and ultimately ferrimagnetic metallic states. This evolution highlights the progressive strengthening of Ti-centered electron correlations and the delicate interplay between crystal-field splitting and enhanced d-d hybridization. DMFT calculations further substantiate these findings by revealing orbital-selective quasi-particle renormalization, incoherent spectral features, and a clear competition between Hund’s coupling and on-site Coulomb repulsion. This competition drives a crossover of these alloys from a correlated semiconducting state to a strongly correlated Hund’s metallic regime.

In fast reactor, based on Plutonium (Pu) fuel, initially the required Pu is derived from the thermal reactor. Once the fast breeder reactor is commissioned then, it can breed more fissile fuel than it consumes, with that further more fast reactors can be commissioned. The vector composition of Pu, depends on the discharged burn up of the fuel from the thermal reactor. Among the Pu isotopes, half-life of Pu-241 is 14.33 years. Since the half-life of Pu241 is 14.33 years and if the discharged fuel (from the thermal reactor) is kept under cooling for long duration, then Pu-241 would decay into Am-241, wherein the Pu-241 is fissile and Am-241 is an absorber of neutron. Though, Am-241 is removed before making the fuel pellets of fast reactor, still analyses are carried out to find out its effect on safety as it is not possible to remove the Am-241 in the already fabricated fuel pin. This study is important, as the presence of Am-241 reduces the delayed neutron fraction and enhances the void co-efficient. With that, when Am-241 is removed and enrichment normalization is done to get the require power and cycle length, the enriched fuel has more Pu and less U-238. This further reduces the Doppler constant and delayed neutron fraction. Analyses are carried out on a medium sized fast reactor to study the impact of Am-241 buildup on fast reactor safety. From the steady state study, it is concluded that, the change in steady state co-efficient with the decay of Pu-241 to Am-241 in three half-life is less than about 6 %. Under transient, the reactor is going to another steady state under UTOPA, it goes to CDA under ULOFA and the mechanical work potential is found to be less than 1 MJ. From the study, it is possible to conclude that, decay of Pu-241 to Am-241 doesn't affect the overall safety of a medium sized sodium cooled fast reactor. The buildup of Am-241 depends on the initial amount of Pu-241, static and dynamic results of a fast reactor are influenced by factors such as reactor fuel, enrichment, size, and shape. Hence these results should be independently verified for other reactors.

The half heusler alloys PdTiX(X= Si Ge, Sn, Pb) focused on their structural, electronic, thermal and thermoelectric properties are investigated by employing first-principles DFT calculations and Boltzmann transport theory. All the concerned materials are observed to be stabilized in its alpha-structural phase(XTiPd) with indirect band-gap. The interplay of partially filled 3d valence electrons of Ti in their localized and hybridized state for determining their stable structural phase and electronic properties is studied in detail. It is found that as X in XTiPd gets substituted in the increasing order of their atomic mass, the band-gap, formation energy, and overall thermal conductivity are reduced considerably. In comparison with other half heusler alloys these materials are obtained with high Seebeck coefficient and moderate electrical and thermal conductivities leading to high figure of merit. Out of all the materials investigated in the present work, SiTiPd is observed with more widened band gap of 0.78 eV and high lattice thermal conductivity of 1L= 27.68 W/m.K whereas PbTiPd has a lowest band gap of 0.38 eV and lowest 1L= 7.64 W/m.K at 300 K. The relaxation time(a) is calculated in the range of 10-13- 10-14 s for all XTiPd using Bardeen and Shockley's deformation potential approximation method. High throughput DFT calculations are performed to extract the accurate thermoelectric efficiency of chosen alloys in terms of figure of merit(zT). An enhanced thermoelectric efficiency of zT =1.4 for SnTiPd at 1200 K, zT = 1.25 for PbTiPd at 1000 K and zT = 1 for XTiPd(X= Si, Ge) at 1200 K are obtained using these throughput calculations. The present study affirms that all the half heusler materials XTiPd(X = Si, Ge, Sn,Pb) can be harnessed as the potential candidates for thermoelectric applications.

The present work is to explore the effect of strain on NiNbAl, half-Heusler alloy. We have investigated the properties of NiNbAl half-Heusler alloy using Density Functional Theory (DFT). The isotropic strains (tensile and compressive) are applied to examine the occurrence of phase transitions in the alloy. Induction of strain alters the electronic, mechanical and thermodynamic properties of the alloy. On application of strain, the alloy undergoes transition from semimetal to direct band gap semiconductor at 4% tensile strain and semimetal to metallic transition at -6% compressive strains. This electronic phase transitions occur due to the change in the interatomic distance between the atoms in the alloy. It is found that the energy band gap value increases up to 12% tensile strain and starts decreasing for the further increase in tensile strain. The mechanical properties of the alloy under strains are analysed and their variation under compressive and tensile strains are compared. The alloy undergoes ductile to brittle transitions on increasing the strain beyond 4%. The phonon dispersion curves for different strains indicate that the alloy is thermodynamically stable under strain. The present results emphasis the effect of strain on electrons, phonons and the mechanical stability of the alloy which will pave way for designing flexible semiconducting devices with suitable device functionalities.

The accurate prediction of safety coefficient such as isothermal temperature coefficient of reactivity is an important requisite in the safe operation of any reactor and also in optimizing the reactor theoretically. At IGCAR, a multi-purpose safety analysis code PREDIS is being used for this purpose by employing the spatial distribution of first order perturbation worth as input. Estimated isothermal temperature coefficient is validated against the measured value of a small 40 MWt carbide core reactor FBTR and 400 MWt FFTF. Though the results are conservative, PREDIS is found to be under predicting the safety coefficients. A detailed parametric study showed that isothermal temperature coefficient is under predicted through PREDIS analysis because of neglecting the contributions of removal worth from the non-fuelled regions surrounding the core. Relative contributions of non-fuelled regions to isothermal temperature coefficient have been systematically quantified in different fast reactor cores such as 40 MWt carbide core of FBTR, 400 MWt FFTF, 1250 MWt oxide core of PFBR and 1500 MWt oxide core of FBR 1&2. From the study, the leakage contribution to the surrounding non-fuelled region is found to be significant in a smaller core, hence the removal worth of these regions should not be ignored while estimating the safety coefficients. Conservative assumptions of considering only the core region for the prediction of safety coefficient is assumed to be good, only for the medium sized reactors, where the leakage contribution to the isothermal temperature coefficient is not that prominent.

In this report, the ground state properties of the half-Heusler GaNiSb, InNiSb and InPdSb alloys in the cubic LiAlSi-type structure, are investigated using the Full Potential Linearized Augmented Plane Wave (FP-LAPW) method as implemented in WIEN2k code, based on Density Functional Theory (DFT). The Perdew–Berke–Ernzerhof (PBE) Generalized Gradient Approximation (GGA) is used for exchange–correlation functional. The calculated formation energies and volume-optimization curves of three different structural configurations (Type 1, Type 2 and Type 3) of these alloys reveal that Type 3 configuration is the most favorable (lowest energy structure) structure. According to the Slater–Pauling rule, the studied alloys are non-magnetic in nature in the stable Type 3 configuration. Therefore, the calculation of ground state properties of these alloys are examined in the Type 3 structural configuration and non-magnetic state. The results of electronic structure and density of states reveal that these alloys are metallic in nature. These alloys are dynamically stable as demonstrated by their calculated phonon dispersion spectra. As the three independent elastic constants C11, C12 and C44 satisfy Born–Huang stability condition, these alloys are stable elastically. The studied alloys are ductile in nature, elastically anisotropic and GaNiSb is found to be stiffer than InNiSb and InPdSb by the calculation of mechanical properties. The present work is in good agreement with the previously reported results.

This paper reports the effect of ternary addition of cobalt to B2 NiTi by varying concentrations x = 0.125, 0.25 and 0.375 in Ni0.5_xCoxTi0.5 and the impact on their crystal structure, electronic and mechanical properties using first-principles calculations. The third element Co was substituted on both Ni and Ti sub-lattices using the supercell approach, site preference energy and formation energy suggest the preference of Co substitution on Ni sub-lattice agreeing with literature. The evolution of the electronic and mechanical properties from undoped NiTi to TiCo by substitution of Ni by Co is hereby discussed. Young's (E) and shear (G) modulus is found to gradually increase as concentration (x) is increased. Importantly, ductility decreases with increasing cobalt concentration. From DOS, it is observed that the delocalized d states are reduced upon increasing Co addition due to strong d -d hybridization which reduces the metallicity and in turn ductility. This increase in Young's modulus and decrease in ductility upon cobalt addition is indicative of the overall stiffness and resistance to deformation.

Bi2Se3 is an established thermoelectric material and has been gaining recent popularity as a topological insulator. This study explores the topological property of Bi2Se3 by performing first principles calculation on Bi2Se3 bulk system and employing the technique of fat band analysis from the projected density of states to visualize the band inversion. Electronic band structures of Bi2Se3 are compared for two cases: before and after including spin-orbit coupling (SOC) and a slight increase in bandgap is observed. Density of states and projected density of states are calculated and compared for both the cases. Band parity analysis suggested by Fu and Kane is employed to establish the strong topological invariant number of Bi2Se3.Therefore this study is aimed at understanding the tell-tale signs of a topological insulator from first principles calculation.

The structural, electronic and magnetic properties of the half-Heusler alloys CrZSi (Z = Sc, Ti) were studied using Density Functional Theory (DFT) based on pseudopotential method to explore the Cr-based ferromagnetic halfmetallic alloys. The effect of substitution of scandium and titanium in Slater-Pauling behaviour, half-metallicity and mechanical properties were studied to understand the role of low valent transition element in half-Heusler compound. CrTiSi shows half-metallicity with an indirect bandgap of the value 0.765 eV. The robustness of halfmetallic behaviour at different hydrostatic pressures were calculated. CrTiSi obeys Slater-Pauling rule and has integer magnetic moment of 4 mu B. The mechanical properties were studied for both CrScSi and CrTiSi compounds to obtain elastic constants and moduli. The present work reveals the ductile nature of the compounds as their B/G ratio is >1.75 with positive Cauchy pressure. Further, phonon calculation with absence of negative frequencies determines the dynamical stability of the compound.

The structural, electronic, elastic and mechanical properties of half-Heusler HfRhZ (Z = As and Sb) alloys are investigated using first principles calculations. The optimized lattice constants, bulk modulus and its pressure derivatives within LDA and GGA approaches are reported. The calculated results of band structure and density of states using GGA and TB-mBJ confirm that HfRhSb is an indirect band gap semiconductor while HfRhAs is a direct band gap semiconductor. The elastic and mechanical properties of HfRhZ (Z = As and Sb) alloys within LDA and GGA approaches are also investigated. The alloys are elastically stable as their elastic constants such as C-11, C-12 and C44 satisfy the mechanical stability condition. The mechanical properties such as Young's modulus (E), bulk modulus (B), shear modulus (G(H)), Poisson's ratio (sigma), the Pugh's ratio (B/G(H)), anisotropic factor (A) and Cauchy's pressure (C-p) are calculated. The studied alloys are ductile in nature, elastically anisotropic and HfRhSb has more stiffness than HfRhAs.

Enriched characteristics like porosity, stability and specific surface area assist TiO2 to find extensive applications in photocatalysis, dye sensitized solar cell, and sensors. TiO2 semiconductor was prepared using titanyl acetylacetonate and characterized by XRD, FTIR, Raman, UV-Vis, FESEM, EDX, and DLS. XRD result confirmed the tetragonal structured anatase TiO2 semiconductor. Scherrer formula is used to calculate crystallite size and the obtained value is 6.81 nm. Microstrain, stress, energy density, and crystallite size are calculated using W-H model. The absorption peak of TiO2 is observed at 652.11 cm(-1) from FTIR spectrum and authenticated the anatase TiO2 semiconductor. The UV absorption edge is identified at 365 nm and the bandgap is calculated from the Kubelka-Munk equation using Tauc plot. Raman spectrum show bands at 140,197, 395, 512, and 635 cm(-1) and these peaks confirmed the presence of the anatase TiO2 stretching mode. FESEM micrographs exhibited agglomerated spherical morphology and the particle size was further analysed using DLS study. The elemental compositions were identified in the EDX analysis. The obtained spectrum showed 55.88 Wt% of O and 44.12 Wt% of Ti atoms. The prepared anatase TiO2 semiconductor indicated enhanced catalytic behaviour. The rate constants and half life time are related to crystallite size using mathematical relation. It is found that the degradation process varies with crystallite size.

The undoped and Ni-doped TiO2 (Ni = 0.1, 0.3, 0.5 M) are synthesized and analyzed for application as dye-sensitized solar cell. The structural, optical and surface properties of the prepared samples are investigated using XRD, FTIR, Raman, UV–Vis, BET and XPS. The morphology and elemental composition of the materials are also studied using FESEM and EDX. The fabricated dye-sensitized solar cells are analyzed using electrochemical impedance spectroscopy and I–V characterization. The XRD studies reveal well crystalline nature of the samples. The anatase phase is confirmed for undoped TiO2 and mixed phase is observed for Ni-doped TiO2. The crystallite size calculated using Scherrer formula is found to increases for 0.1 and 0.3 M Ni metal ions doped into TiO2 lattice, beyond 0.3 M concentration it tends to decrease. The Raman peaks show the shift towards lower wave number upto 0.3 M Ni concentration, beyond this it tends to shift to higher wavenumber. Absorption spectra show the redshift for Ni doped TiO2 and the obtained optical bandgap for undoped and Ni doped TiO2 (Ni = 0.1, 0.3, 0.5 M) are 3.08, 2.53, 2.26, and 2.39 eV respectively. From the FESEM analysis the spherical shape morphology is observed and the element composition of Ti, O, Ni are confirmed by the EDX analysis. The specific surface area and pore size are calculated using BET analysis. The XPS is used to analyze the chemical environment and it confirms the successful Ni ions insertion into TiO2 lattice sites. The charge transfer resistance, shunt resistance and electron life time are calculated from electrochemical impedance study, which shows that the charge recombination can be reduced through Ni dopant. The obtained results show an interesting feature for Ni metal ions concentration beyond 0.3 M in TiO2 nanostructure. From XRD, Raman and UV–Vis results, there seems to be a threshold for the concentration 0.3 M of Ni in TiO2. Enhanced photocurrent conversion efficiency is obtained for 0.3 M Ni doped TiO2 photoanode-based DSSC.

The design experience of PFBR (Prototype Fast Breeder Reactor) gives confidence in designing advanced Sodium cooled Fast Reactors (SFR) with improved economy and passive safety features towards enhanced safety. In this regard, Fast Breeder Reactor (FBR) is optimised with 600 MWe leading to better economy. To prevent severe core damage & large radioactivity release to the public and also to enhance the safety, improved inherent safety characteristics are adopted with passive shutdown features. Important safety measures taken to improve inherent safety are the optimization of sodium void reactivity beneath 1 $, which is in line with the current international thinking. To incorporate the enveloping beyond design basis events (BDBE) within the Design Extension Condition (DEC), additional passive safety mechanisms are envisaged to strengthen the reactor safety and practically eliminate the probability of Core Disruptive Accidents (CDA). One such BDBE is Unprotected Transient Over Power Accident (UTOPA), in which uncontrolled withdrawal of one control rod leads to rise in power and fuel temperature. Under UTOPA, it is possible for fuel to melt and undergo in-pin fuel motion through the available central hole. Upon initiation of melting, fission gases trapped within the fuel microstructure are released into the pellet cavity along with molten fuel. Consequently, a multi-phase flow occurs inside the pellet cavity, with several hydrodynamic effects influencing the fluid motion. The relocation of molten fuel from high fuel void worth to low fuel void worth region results in a negative reactivity feedback. This in-pin fuel motion or squirting feedback reduces the total reactor power as well as the hot-spot clad and coolant temperatures. With change in reactor power during UTOPA, the balance of the plant gets affected. This results in a change in the inlet coolant temperature, which affects the overall core temperature profile and its respective feedbacks. Considering the above said arguments, UTOPA study has been carried out with different initial conditions such as Constant Inlet Coolant Temperature (CICT), Time Dependent Inlet Coolant Temperature (TDICT), with and without In-Pin Fuel Motion (IPFM) feedback. Comparisons of the results are made to get better understanding of various feedbacks and their impact on UTOPA, highlighting the importance of in-pin fuel motion reactivity feedback in a medium sized fast reactor core. From the study, it is concluded that the case without considering IPFM feedback gives the most conservative results and if the transients converge to a safe state without considering IPFM feedback then, the transients are expected to settle down to a safe state with IPFM feedback.

A viable alternative approach fir the synthesis of metal and oxide nanmaterials is the low cost nontoxic biosynthesis method. In this study, TiO 2 nanoparticles were synthesized using the lemon leaf extract. Calcining the synthesized powder at 150–450 °C resulted in single phase anatase spherical particles (6–14 nm) of titania and band gap decreased from 3.34 to 3.29 eV. Raman studies exhibit the prominent bands assignable to the anatase phase. MB blue dye degraded by 94% in 180 min (pH-11). The nanoparticles could be reused for eight cycles with a 4% decrease in the degradation efficiency.

The present study, describes the structural, electrical, and the photocatalytic activity of sol-gel synthesized TiO2-ZnO nanostructure. The synthesized mixed oxide nanostructure is characterized by XRD, FTIR, Raman, UV-Vis, FESEM, DLS and Impedance Spectroscopy analyses. In addition, photocatalytic activity of multiphase TiO2 (TAB)-ZnO (ZW) nanostructure is analysed using Methylene Blue dye as the model dye under UV and Visible light illumination. The XRD analysis confirms the bi-phase TiO2 and mono-phase ZnO in the multiphase TiO2-ZnO nanostructures. The average crystallite size of 33 nm has been estimated using Scherrer formula. The crystallite size and mechanical properties such as strain, stress, and other parameters are analysed using Williamson-Hall model. The FTIR spectrum shows the characteristics absorption peaks of TiO2 and ZnO at 679.44 and 432.79 cm(-1) respectively, and reveals the presence of TiO2 and ZnO in the synthesized multiphase nanostructure. The optical band gap is calculated using Tauc relation with the data obtained from UV-Vis spectrometer. The calculated band gap value is 3.1 eV. The FESEM study shows the spherical morphology and the DLS analysis confirms the particle size is 433 nm. The presence of Ti-O and Zn-O stretching modes are confirmed from Raman spectrum. The electrical properties such as dielectric constant, dielectric loss, and ac conductivity are analysed from impedance data. The prepared multiphase TiO2 (TAB)-ZnO (ZW) nanostructure shows better photocatalytic activity in both UV and visible light region. The rate constant has been calculated as 0.0083 and 0.0052 min(-1) for UV and visible light irradiation.

Dye Sensitized Solar Cell (DSSC) is fabricated using Zn+Mg co-doped TiO2 nanoparticles. The structural, optical, electrical, morphology and elemental composition of the materials are studied using XRD, UV-Vis, EIS, FESEM, EDX techniques. The I-V characterization of DSSC device are analysed. The X-ray diffraction studies reveal well crystalline nature. The absorption spectrum and optical bandgap of prepared co-doped TiO2 clearly show the visible light behaviour. The FESEM analysis show spherical shape particle and the element composition (Ti, O, Zn, Mg) is confirmed by the EDX analysis. The obtained photocurrent conversion efficiency (PCE) is 2.08 % for Zn+Mg co-doped TiO2 photoanode based DSSC device.

In this report, the structural, electronic, magnetic and thermoelectric properties of CoX′NbGa (X′ = Cr, Mn, Fe) quaternary Heusler alloys are investigated using the full potential linearized augmented plane wave method in combination with the semi-classical Boltzmann transport theory. The exchange and correlation effects are treated using generalized gradient approximation and modified Becke-Johnson scheme. Our results reveal that CoCrNbGa and CoFeNbGa are half-metallic ferrimagnets satisfying the well-known Slater Pauling rule Mt = Zt − 24 from the analysis of electronic and magnetic properties. The half-metallic behaviour of CoCrNbGa and CoFeNbGa are robust against hydrostatic strain for a considerably wide range of lattice constants which makes them potential candidates for spintronic applications. CoMnNbGa is a non-magnetic 24 valence electron semiconductor and has better thermoelectric performance than CoCrNbGa and CoFeNbGa.