Dixit, Ambesh

2022-08-01, Kumar, Rohitash, Nirwan, Anju, Mondal, Bobin, Kumar, Ravindra, Dixit, Ambesh

We investigated the impact of thermally expanded graphite (ExG) on thermal conductivity and charging/discharging time for pristine pentadecane (PD), a potential phase change material for low-temperature thermal energy storage applications. The expanded graphite is prepared using a high-temperature (~ 950 ℃) thermal shock on chemically treated natural graphite flakes and is vacuum impregnated in pentadecane. Four different 5, 10, 15, and 20 mass% expanded graphite and pentadecane (PD-ExG) composite samples are considered for intensive studies of their thermophysical properties using differential scanning calorimeter (DSC), temperature history (T-history), and transient plane source measurements. DSC measurements showed the reduction in latent heat of fusion of pentadecane with increased mass% of ExG, but the melting temperature remained nearly unaffected. Further, thermal conductivity of pentadecane-expanded graphite composites enhanced from ~ 0.18 W m−1 K−1 (for pristine pentadecane) to 1.1 W m−1 K−1, 2.6 W m−1 K−1, 4.7 W m−1 K−1, and 7.1 W m−1 K−1 for 5, 10, 15, and 20 mass% ExG composite samples, respectively. The discharge time for these PD-ExG composites reduced about 42.7 to 67.81% as compared to pristine PD sample. PD-ExG composite with 10% or more ExG also showed the shape stability of PD-ExG composites and thus reduced leakage of PD in liquid state. Thus, PD-ExG form stable phase change material composite with enhanced thermal conductivity and enhanced charge/discharge rate, making it a suitable PCM for low-temperature thermal energy storage system such as space cooling.

2023-01-01, Sahoo, Priyambada, Saini, Lokesh, Dixit, Ambesh

Implementation of stealth features on advanced airborne platforms (aircrafts, unmanned air vehicles, missiles, etc.) has become a compulsion for each country, for denial/delay detection of these objects from enemy radars, during tactical missions. Apart from the shaping of the airframe, implementation of microwave-absorbing materials (MAMs) on identified locations of airborne vehicles is the only viable solution to reduce their radar cross-section (RCS) and eventually attain stealth capabilities. Numerous dielectric and magnetic class materials have been developed over the last few decades to fulfil the requirement for RCS reduction against various radars operating in different frequency ranges. In this review, a detailed representation of almost the entire range of materials used as MAMs has been provided along with their possible microwave (MW) loss mechanism to fill the gap that existed for a systematic insight on MAMs till now. The current limitations and future aspects are also discussed for the development of future stealth materials.

2023-11-02, Kumar Yadav, Ankit, Prakash, Chandra, Pandey, Akhilesh, Dixit, Ambesh

Cu2ZnSnS4 (CZTS) active material-based resistive random-access memory (RRAM) devices are investigated to understand the impact of three different Cu, Ag, and Al top electrodes. The dual resistance switching (RS) behaviour of spin coated CZTS on ITO/Glass is investigated up to 102 cycles. The stability of all the devices (Cu/CZTS/ITO, Ag/CZTS/ITO, and Al/CZTS/ITO) is investigated up to 103 sec in low- (LRS) and high- (HRS) resistance states at 0.2 V read voltage. The endurance up to 102 cycles with 30 msec switching width shows stable write and erase current. Weibull cumulative distribution plots suggest that Ag top electrode is relatively more stable for set and reset state with 33.61 and 25.02 shape factors, respectively. The charge carrier transportation is explained by double logarithmic plots, Schottky emission plots, and band diagrams, substantiating that at lower applied electric field intrinsic copper ions dominate in Cu/CZTS/ITO, whereas, at higher electric filed, top electrodes (Cu and Ag) dominate over intrinsic copper ions. Intrinsic Cu+ in CZTS plays a decisive role in resistive switching with Al electrode. Further, the impedance spectroscopy measurements suggest that Cu+ and Ag+ diffusion is the main source for the resistive switching with Cu and Ag electrodes.

2020-01-01, Deb, Dipankar, Chandra, Laltu, Dixit, Ambesh

2024-03-01, Kale, Abhijeet J., Pal, Biswajit, Dixit, Ambesh

Herein, density functional theory-based comparative studies on cubic CsMX3 (M-: Pb, Sn, Ge; X-: Cl, Br, I) and rhombohedral CsGeI3 perovskites are reported. The structural stability indicator analysis shows that Ge-based perovskites may exhibit small rhombohedral distortion led by lone pair (4 (Formula presented.)) electrons on off-centering Ge atom. The role of lone pair on Ge atom in rhombohedral distortion is corroborated by bond length, electronegativity, and charge density distributions. Nearly agreeable bandgap ((Formula presented.)) values are noticed for cubic CsPbX3 (X-: Cl, Br, I) and rhombohedral CsGeI3, and the corresponding values are 3.04, 2.30, 1.72, and 1.45 eV, respectively. The effect of Jishi et al. reparameteried Tran–Blaha-modified Becke–Johnson exchange-correlation (XC) potential is discussed in context of optoelectronic properties. The changes in bandgap are attributed to the lifting of electronic degeneracy either by spin-orbit coupling or symmetry lowering in rhombohedral distortion. The rhombohedral CsGeI3 is thus further emphasized to account its ferroelectricity with computed total polarization ((Formula presented.)) around 32.75 μC cm−2. The suitable (Formula presented.) (1.45 eV), high absorption (≈105 cm−1), tolerable reflectivity (19%), and carrier effective masses (0.61 and 0.27) enable rhombohedral CsGeI3 (superior 30.5% spectroscopy-limited maximum efficiency [SLME] at 1 μm thickness) to outperform conventional CsPbI3 (27.6% SLME at 1 μm) and others which may attract PV community to further address its underexplored promise.

2024-04-25, Sahoo, Priyambada, Tiwari, Chandni, Kukreti, Sumit, Dixit, Ambesh

We report the photovoltaic response of bismuth ferrite (BiFeO3) multiferroic absorber based all oxide FTO/ZnO/BiFeO3/Au solar cell using density functional theory for materials optoelectronic properties and macroscopic device simulation-based hybrid approach. The structural, electronic, and optical properties of BiFeO3 are investigated using density functional theory (DFT). The band structure and density of states of R3c-BiFeO3 are computed considering the Hubbard parameter Ueff∼4.2eV for both Fe-3d and O-2p orbitals for matching the experimental bandgap of ∼2.5eV. The computed optical properties, such as absorption for rhombohedral R3c-BiFeO3 are used to investigate FTO/ZnO/BiFeO3/Au solar cell performance using a macroscopic device simulation approach. The thickness, acceptor concentration, defect concentration of the absorber layer, interface defect density, electron affinity of the electron transport layer, and the impact of series, shunt resistance, and metal back contact are investigated to optimize the photovoltaic response under realistic conditions. The optimum photoconversion efficiency (PCE) is ∼11.92% with open circuit voltage (Voc) of 1.033V, short circuit current density (Jsc) of 15.27mA/cm2, and fill factor (FF) of 75.59%. This study on BiFeO3-based absorber materials opens a way to realize lead-free perovskite absorber material with a potential for realizing all oxide solar cells.

2019-10-01, Chaurasiya, Rajneesh, Gupta, Goutam Kumar, Dixit, Ambesh

Two-dimensional layered transition metal dichalcogenide exhibit important characteristics such as suitable bandgap, high absorption coefficient, and favourable electron transport properties for their uses in nano-electronic such as ultrathin solar cells. We adopted a hybrid simulation approach, where density functional calculations are performed for optoelectronic properties of semiconductor materials and macroscopic device simulation is carried out to evaluate photovoltaic response. We investigated electronic and optical properties of bulk WS2, WSe2 and noticed very high absorption coefficient, making them suitable absorber materials for solar cell. Further, the electronic and optical properties of an ultrathin WSSe Janus layer are investigated using density functional theory and noticed low reflectance and high bandgap, supporting its usefulness as a buffer layer for W(S/Se)2 absorbers. The computed density functional results for W(S/Se)2 and Janus WSSe are used to simulate the photovoltaic response of WSSe/W(S/Se)2 solar cell using macroscopic device simulation. The photovoltaic performance of a single junction solar cell is optimized for W(S/Se)2 absorbers and WSSe Janus buffer materials. The effect of absorber layer thickness, carrier concentration, and contact work function is evaluated to understand the solar cell performance. We noticed that interface recombination speed between absorber and buffer layer and minority carrier lifetime are affecting the solar cell performance. The maximum efficiency of about ~17.73% and 18.87% is noticed for optimized WSSe/WS2 and WSSe/WSe2 solar cell. The present study will provide a new approach to design, develop, and optimize a solar cell and evaluate the impact of different materials parameters on solar cell performance.

2020-02-01, Kumari, Chandni, Varun, Ishan, Tiwari, Shree Prakash, Dixit, Ambesh

BiFeO3 based resistive random access memory (RRAM) devices are fabricated using a low-cost solution process to study the effect of an Al top electrode on switching behavior and reliability. Fabricated devices demonstrated bipolar switching characteristics with a moderate Ion/Ioff ratio, set and reset voltages of ∼-1.3 V and ∼0.8 V, DC and AC endurance of more than 250 cycles and 7100 cycles, respectively, and a retention time of over 104 s, confirming the non-volatile resistive switching behavior. The ohmic and trap filled space charge limited conduction dominates the conduction mechanism in the devices at lower and higher voltages, respectively. Moreover, impedance spectroscopy measurements substantiate the presence of an AlOx layer at the Al/BiFeO3 interface resulting from the Al-O interaction at the junction, which is the possible rationale of reliable complementary switching in these RRAM devices. The switching mechanism is elucidated using the formation and rupture of the oxygen vacancy mediated filament, assisted by the participation of a thin AlOx layer at the Al/BFO interface. The role of the thin AlOx layer is explained by modeling of impedances.

2022-09-01, Prakash, Chandra, Dixit, Ambesh

Using a low-cost hydrothermal method, we demonstrated the fabrication of phase pure rutile phase high-density vertically aligned TiO2 nanorods-based catalyst-free hydrogen (H2) gas sensor. The synthesized TiO2 nanorods on FTO are decorated with the aluminum interdigitated electrode pattern for electrical measurements. TiO2 nanorods-based hydrogen sensor showed the optimum response of ∼53.18% at 150 ppm H2 concentration relative to air at 100 °C. The measured response and recovery time of TiO2 nanorods are 85 and 620 s, respectively. The TiO2 nanorods-based H2 gas sensor showed a relatively better response, good reproducibility, and stability at moderate temperatures, i.e., 50 and 100 °C. The electrochemical impedance measurements showed a small variation in the surface characteristics of TiO2 nanorods before and after exposing H2 gas. The carrier lifetime at 50 °C and 100 °C at 150 ppm are 5 μs and 3 μs, respectively. Interestingly, H2 selectivity is also observed against H2S, CO, and NH3 gases, suggesting that high-density vertically aligned TiO2 nanorods can be a good candidate for efficient hydrogen sensing at relatively low temperatures.

2014-01-01, Sahu, Anurag, Dixit, A., Hiremath, Kirankumar R.

We investigated the effect of Au nanoparticles in Zinc o xide semiconductor matrix for enhanced absorption. Apart from ZnO optical absorption at 360 n m, the matrix also shows plasmonic absorption at 560 nm.