
Venkata Sai Kiran ChakravadhanulaSkyroot Aerospace Private Limited
Venkata Sai Kiran Chakravadhanula
PhD, Masters, B-Tech
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Publications (151)
Polymer pyrolysis has emerged as a versatile method to synthesize graphenoid (graphene like) materials with varying thickness and properties. The morphology of the thin film, especially the thickness, greatly affects the graphitizability and the properties of the graphenoid material. Using in situ current annealing inside a transmission electron mi...
Performing reliable preparation of TEM samples is the necessary basis for a meaningful investigation by ex-situ and even more so by in-situ TEM techniques, but it is challenging using materials that are sensitive to electron-beam irradiation. FIB is currently the most commonly employed technique for a targeted preparation, but the structural modifi...
Aluminum alloy (AA2219) is widely used for the fabrication of earth storable and cryogenic propellant tanks. To ensure flight safety, it is important to understand the effect of long-term storage on the mechanical properties, which are dependent on the microstructure. Therefore, the present work is carried out to understand the effect of long term...
XH 67 is a nickel-based superalloy, which is used in critical parts of modern aerospace engines. In the present study, XH 67 specimens in five different heat treatment conditions selected based on the processing and application have been investigated for their microstructures, morphology, and composition of the matrix and second-phase particles. Op...
Streaming current measurements were used to study the interaction of polyoxometalates (POMs) and nanoparticles (NPs) with flat surfaces as an alternative, innovative approach to infer POM and NP properties of potential sparse material in terms of charge and magnitude. With respect to POMs, the approach was able to reveal subtle details of charging...
The high-temperature deformation behavior of nickel-base superalloy IN718 was investigated in the solution-treated (ST) condition. High-temperature tensile tests were performed between 600 °C and 850 °C at strain rates of 1 × 10−3, 1 × 10−2, and 1 × 10−1 s−1. The deformation behavior of this material was analyzed using optical microscopy, scanning...
A focused ion beam (FIB) system is used to fabricate a micron-sized all-solid-state fluoride ion cell from a bulk battery for in situ transmission electron microscopy (TEM) testing. The bulk battery is based on a La0⋅9Ba0⋅1F2.9 solid-state electrolyte with a nanocomposite of Cu/C as a cathode and a nanocomposite of MgF2, Mg, La0⋅9Ba0⋅1F2.9 and C as...
Spark plasma sintering aids in characteristic eutectic structure free microstructural evolution in hypereutectic Al-Si. The mechanism of suppression of characteristic eutectic was elucidated through current-voltage evolution during sintering, electron backscatter diffraction phase mapping and high-angle annular dark field imaging. The electric curr...
55Ni-17Cr-12Fe-9Mo-2Nb-1.5Al alloy is a nickel-based superalloy (Russian designation is XH55MбЮ or KhN55MBYu, XH55) without any equivalent in American/European alloy designation. It is used in cryogenic engine of satellite launch vehicles application in two different heat-treated conditions: (1) standard aged (STA) at 730 °C/15 h + 650 °C/10 h and...
Oxidation behavior of tungsten disulphide (WS2) nanosheet powder with an average thickness of about 10 nm was studied in the temperature range of 25-700°C. The samples were subjected to exposures in air in a short continuous mode as well as extended isothermal holding. It was observed that WS2 nanosheets were stable below 350°C in air on short expo...
Ti-5Al-5V-2Mo-1Cr-1Fe (Ti-55211) is another popular (α+β)-Ti alloy which exhibits good hardenability and high strength due to the formation of α′ martensite. In the present study, this alloy in the as-forged and heat treated conditions was investigated to evaluate the tensile behavior as a function of test temperature (from room temperature to near...
In situ transmission electron microscope (TEM) characterization techniques provide valuable information on structure–property correlations to understand the behavior of materials at the nanoscale. However, understanding nanoscale structures and their interaction with the electron beam is pivotal for the reliable interpretation of in situ / ex situ...
Transition metal fluorides are an important class of cathode materials for lithium batteries owing to their high specific energy and safety. However, metal fluorides are electrical insulators, exhibiting slow reaction kinetics with Li. Consequently, metal fluorides can show poor electrochemical performance. Instead, carbon-metal fluoride nanocompos...
Efforts made in this current study focus on the development of a novel, simple, cost-effective yet efficient approach to synthesize nanoporous carbon material from corn silk biomass for supercapacitor applications. We have employed different activation approaches in order to obtain a higher surface area and large mesoporous volume fraction. The per...
Development of highly efficient batteries with more rational understanding and precise control of the underlying microstructural features requires high resolution based characterization tools. Electron microscopy and spectroscopy offers information about the structure, morphology, chemistry and chemical composition of the battery materials on nano...
Electrodes prepared by electrospinning often exhibit an activation behavior, i. e. they are reaching their full capacity only after numerous charge and discharge cycles. The activation mechanism can be explained by the improvement of the accessibility of Li⁺ ions to the active particles of the cathode, which increases with the number of cycles. It...
Electron Beam Effects on Silicon Oxide Films – Structure and Electrical Properties - Volume 24 Supplement - Krishna Kanth Neelisetty, Sebastian Gutsch, Falk von Seggern, Alan Molinari, Alexander Vahl, Xiaoke Mu, Torsten Scherer, Chakravadhanula VS Kiran, Christian Kübel
Chemical doping via insertion of ions into the lattice of a host material is a key strategy to flexibly manipulate functionalities of materials. In this work, we present a novel case study on the topotactic insertion of fluoride ions into oxygen-deficient ferromagnetic thin films of La0.74Sr0.26MnO3−δ (LSMO) epitaxially grown onto single-crystal Sr...
In this work, the electrostatic self-assembly of LiFePO4 particles coated with polyelectrolytes on a three-dimensional carbon substrate is described. This new fabrication method allows precise control of ionic and electronic conduction pathways as well as the interfaces between the different electrode components, thus enabling new strategies for ta...
Oxide semiconductors typically show superior device performance compared to amorphous silicon or organic counterparts, especially, when they are physical vapor deposited. However, it is not easy to reproduce identical device characteristics when the oxide field-effect transistors (FETs) are solution-processed/ printed; the level of complexity furth...
A rigid crystal lattice, where cations occupy specific positions in the lattice, is generally regarded a critical requirement to enable Li+ diffusion in the bulk of conventional cathode materials, while disorder is generally considered as detrimental. Herein, we demonstrate that facile and reversible insertion and extraction of Li+ is possible with...
The use of functional nanomaterials is a common strategy to improve the mechanical and electrochemical properties of silicon anodes for secondary lithium-ion cells. Here, we report the preparation of a structurally stable composite material with a unique morphology comprising small-size silicon particles and especially branched carbonaceous nanofib...
A continuous process of synthesizing ultrafine aluminum powder (UFAP) having high yield rate using RF induction plasma is reported in the current work. The processing parameters (powder injection probe position; powder feed rate; flow rates of gases for plasma forming, quenching and passivation) were varied systematically to evaluate their influenc...
Double-walled carbon nanotubes (DWCNTs) consist of two coaxially aligned single-walled carbon nanotubes (SWCNTs), and previous sorting methods only achieved outer-wall electronic-type selectivity. Here, a separation technique capable of sorting DWCNTs by semiconducting (S) or metallic (M) inner- and outer-wall electronic type is presented. Electron...
The physical properties of the calcium silicate hydrate phase (C-S-H) greatly impact material strength and durability of cement-based materials. However, despite its widespread use and influence on material stability, there is still debate concerning its nanostructure. In this paper, the pore structure of C-S-H was characterized by analyzing focuse...
Graphitization of polymers is an effective way to synthesize nanocrystalline graphene on different substrates with tunable shape, thickness and properties. The catalyst free synthesis results in crystallite sizes on the order of a few nanometers, significantly smaller than commonly prepared polycrystalline graphene. Even though this method provides...
Graphitization and Growth of free-standing Nanocrystalline Graphene using In Situ Transmission Electron Microscopy - Volume 23 Issue S1 - C.N. Shyam Kumar, Venkata Sai Kiran Chakravadhanula, Adnan Riaz, Simone Dehm, Di Wang, Xiaoke Mu, Ralph Krupke, Christian Kiibel
Lithium ion battery is currently the method of choice when it comes to local stationary storage of electrical energy. In the search for an alternative system, fluoride ion battery (FIB) emerges as a candidate due to its high theoretical capacity, and no lithium is needed for its operation. To improve the cycling performance and lower the working te...
Lithium ion battery is currently the method of choice when it comes to local stationary storage of electrical energy. In the search for an alternative system, fluoride ion battery (FIB) emerges as a candidate due to its high theoretical capacity, and no lithium is needed for its operation. To improve the cycling performance and lower the working te...
In the search for novel battery systems with high energy density and low
cost, fluoride ion batteries have recently emerged as a further option to store
electricity with very high volumetric energy densities. Among metal fluorides,
CuF2 is an intriguing candidate for cathode materials due to its high specific
capacity and high theoretical conversio...
In the search for novel battery systems with high energy density and low cost, fluoride ion batteries, which are based on F- anion shuttle, recently emerge as alternative for current lithium ion battery systems. Among metal fluorides, CuF2 is an intriguing candidate for the cathode material due to its high specific capacity and high theoretical con...
Memristors based on a double barrier design have been analysed by various nano spectroscopic methods to unveil details about its microstructure and conduction mechanism. The device consists of an AlOx tunnel barrier and a NbOy/Au Schottky barrier sandwiched between Nb bottom electrode and Au top electrode. As it was anticipated that the local chemi...
Memristors based on a double barrier design have been analysed by various nano spectroscopic methods to unveil details about its microstructure and conduction mechanism. The device consists of an AlOx tunnel barrier and a NbOy/Au Schottky barrier sandwiched between Nb bottom electrode and Au top electrode. As it was anticipated that the local chemi...
Mg-based batteries, which use the Mg2+ shuttle, theoretically offer several advantages compared to the Li technology, such as higher theoretical volumetric capacity (3833 mA h cm−3) of the Mg-metal anode, the possibility to be safely handled in air, and dendrite-free electrodeposition. In this study, vanadium oxychloride was employed as an electrod...
Barium ferrite and its hydrated form (BaFeO2.5−x+δ (OH)2x , BFO) is an interesting cathode material for protonic ceramic fuel cells (PCFC) due to its potential to be both, conducting for electrons and protons. We report on the fabrication of almost epitaxially grown thin films (22 nm) of barium ferrite BaFeO~2.5 (BFO) on Nb-doped SrTiO3 substrates...
Cement-based materials play a vital role in our modern day concrete environment. During service life, they are often in contact with different aqueous solutions, which lead to structural and chemical changes and in turn, a possible deterioration of this material. Transport processes and intrinsic material properties are key components of such react...
With the aim to synthesize soluble cluster molecules, the silver salt of (4-(tert-butyl)phenyl)methanethiol [AgSCH2C6H4
t
Bu] was applied as a suitable precursor for the formation of a nanoscale silver sulfide cluster. In the presence of 1,6-(diphenylphosphino)hexane (dpph), the 115 nuclear silver cluster [Ag115S34(SCH2C6H4
t
Bu)47(dpph)6] was obta...
Graphene is of increasing interest for optoelectronic applications exploiting light detection, light emission and light modulation. Intrinsically light matter interaction in graphene is of a broadband type. However by integrating graphene into optical micro cavities also narrow band light emitters and detectors have been demonstrated. The devices b...
Multicomponent entropy stabilised oxides containing four and five metal elements in equiatomic amounts were successfully synthesised in nanocrystalline form by nebulised spray pyrolysis (NSP), flame spray pyrolysis (FSP) and reverse co-precipitation (RCP) techniques, demonstrating that entropy stabilisation of these recently discovered materials is...
A facile water based synthesis method for HTB-FeF 3 /rGO and r -FeF 3 /rGO composites was developed using FeF 3 nanoparticles prepared by ball-milling and aqueous graphene oxide precursor. Electrodes of HTB-FeF 3 /rGO were cast in ambient air and the calendered electrode shows a stable specific energy of 470 Wh kg –1 (210 mAh g –1 , 12 mA g ⁻¹ ) af...
Lithium iron phosphate (LiFePO4, LFP) is one of the most promising cathode materials for the next generation of Li ion batteries and attracts great attentions. Experimental mapping the lithiated (LFP) and delithiated phase (FePO4, FP) at nanoscale resolution provides knowledge on the microscopic mechanism of the reaction processes during electrical...
A meticulous examination of transient stages of dynamic processes at the micrometer, nanometer or atomic scale is the aim in the field of in situ transmission electron microscopy. Studying a specimen in a state close to its native environment without drying possibly leading to structural alterations, triggers research in the field of in situ liquid...
Multicomponent rare earth oxide (REO) nanocrystalline powders containing up to seven equiatomic rare earth elements were successfully synthesized in a single-phase CaF2-type (Fm-3 m) structure. The addition of more than six elements resulted in the formation of a secondary phase. Annealing at 1000°C for 1 h led to the formation of a single-phase (I...
div class="title"> Comparison of energy filtered TEM spectra image and automated crystal orientation mapping in LiFePO 4 /FePO 4 phase mapping
- Volume 22 Issue S3 - Xiaoke Mu, Aaron Kobler, Venkata Sai Kiran Chakravadhanula, Paul Norby, Christian Kubel
A facile water based synthesis method for HTB-FeF 3 /rGO and r -FeF 3 /rGO composites was developed using FeF 3 nanoparticles prepared by ball-milling and aqueous graphene oxide precursor. Electrodes of HTB-FeF 3 /rGO were cast in ambient air and the calendered electrode shows a stable specific energy of 470 Wh kg –1 (210 mAh g –1 , 12 mA g ⁻¹ ) af...
Trustworthy preparation and contacting of micron-sized batteries is an essential
task to enable reliable in situ TEM studies during electrochemical biasing. Some of the challenges and solutions for the preparation of all-solid-state batteries for in situ TEM electrochemical studies are discussed using an optimized focused ion beam (FIB) approach. I...
A facile water based synthesis method for HTB-FeF3/rGO and r-FeF3/rGO composites was developed using FeF3 nanoparticles prepared by ball-milling and aqueous graphene oxide precursor. Electrodes of HTB-FeF3/rGO were cast in ambient air and the calendered electrode shows a stable specific energy of 470 Wh kg−1 (210 mA h g−1, 12 mA g−1) after 100 cycl...
Trustworthy preparation and contacting of micron-sized batteries is an essential task to enable reliable in situ TEM studies during electrochemical biasing. Some of the challenges and solutions for the preparation of all-solid-state batteries for in situ TEM electrochemical studies are discussed using an optimized focused ion beam (FIB) approach. I...
Trustworthy preparation and contacting of micron-sized batteries is an essential task to enable reliable in situ TEM studies during electrochemical biasing. Some of the challenges and solutions for the preparation of all-solid-state batteries for in situ TEM electrochemical studies are discussed using an optimized focused ion beam (FIB) approach. I...
Transport processes between aqueous solutions and cement-based materials are a key component of reactions which lead to a reduction of durability. The transport processes within capillary pores are already well established as opposed to the influence of the pore system on the nanoscale. To determine the potential impact of the gel pores of the calc...
Graphene is extensively investigated and promoted as a viable replacement for
graphite, the state-of-the-art material for lithium-ion battery (LIB) anodes,
although no clear evidence is available about improvements in terms of cycling
stability, delithiation voltage and volumetric capacity. Here we report the
microwave-assisted synthesis of a novel...
Metal oxyfluoride compounds are gathering significant interest as cathode materials for lithium ion batteries at the moment because of their high theoretical capacity and resulting high energy density. In this regard, a new and direct approach is presented to synthesize phase-pure vanadium oxyfluoride (VO2F). The structure of VO2F was identified by...
This work highlights a strategy for the one-step synthesis of FeAu nanoparticles by the pulsed laser ablation of alloy targets in the presence of different solvents. This method allows particle generation without the use of additional chemicals; hence, solvent-metal interactions could be studied without cross effects from organic surface ligands. A...
Graphene is considered as replacement for graphite, the state-of-the-art material for lithium-ion battery (LIB) anodes. However, it is not clear whether it can really outperform graphite in terms of delithiation voltage, cycling stability and volumetric capacity. In this respect, we present a novel ionic liquid microwave-assisted synthesis of Fe3O4...
A novel room temperature rechargeable battery with VOCl cathode, lithium anode, and chloride ion transporting liquid electrolyte is described. The cell is based on the reversible transfer of chloride ions between the two electrodes. The VOCl cathode delivered an initial discharge capacity of 189 mAh g(-1) . A reversible capacity of 113 mAh g(-1) wa...
Conversion materials have gained significant interest as electrode materials for lithium-ion batteries. The anchoring of active materials in a conductive carbon matrix is a key to achieve high capacities with long cycle life. The cover picture illustrates the use of anion intercalated carbon for the synthesis of respective carbon–metal salt nanocom...
A novel room temperature rechargeable battery with VOCl cathode, lithium anode, and chloride ion transporting liquid electrolyte is described. The cell is based on the reversible transfer of chloride ions between the two electrodes. The VOCl cathode delivered an initial discharge capacity of 189mAhg-1. A reversible capacity of 113mAhg-1 was retaine...
Herein, Fe-doped tin oxide is presented for the first time as new high-capacity lithium-ion anode material.
Pure SnO2, Fe-doped SnO2 (Sn0.9Fe0.1O2, SFO), and carbon-coated SFO (SFO-C) were synthesized and morphologically and electrochemically characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, Brunauere...
Metal fluoride based conversion materials have gained interest as cathode materials for lithium batteries due to their high theoretical energy densities. However, metal fluorides are electrically insulating and experience large volume changes during the charge and discharge processes. Effective synthesis of carbon-metal fluoride nanocomposites with...
Nanoglasses are noncrystalline solids with a granular nano-/microstructure. In contrast to their nanocrystalline analogs, typically constituted of grains and grain boundaries, nanoglasses consist of glassy regions with a structure corresponding to melt-quenched glasses and amorphous interfaces characterized by a reduced density. Their unique proper...
Here we report for the first time the development of a Mg rechargeable battery using a graphene-sulfur nanocomposite as the cathode, a Mg-carbon composite as the anode and a non-nucleophilic Mg based complex in tetraglyme solvent as the electrolyte. The graphene-sulfur nanocomposites are prepared through a new pathway by the combination of thermal...
Here we report for the first time the development of a Mg rechargeable battery using a graphene–sulfur nanocomposite as the cathode, a Mg–carbon composite as the anode and a non-nucleophilic Mg based complex in tetraglyme solvent as the electrolyte. The graphene–sulfur nanocomposites are prepared through a new pathway by the combination of thermal...
Graphene is of increasing interest for optoelectronic applications exploiting light detection, light emission and light modulation. Intrinsically, the light–matter interaction in graphene is of a broadband type. However, by integrating graphene into optical micro-cavities narrow-band light emitters and detectors have also been demonstrated. These d...
Graphene is of increasing interest for optoelectronic applications exploiting light detection, light emission and light modulation. Intrinsically, the light–matter interaction in graphene is of a broadband type. However, by integrating graphene into optical micro-cavities narrow-band light emitters and detectors have also been demonstrated. These d...
The increasing demand for energy storage resulted in improving the performance of Lithium ion batteries (LIB) and a continuing search for alternative battery technologies. Reversible batteries based on a fluoride anion shuttle (fluoride ion battery) are an interesting alternative to LIBs [1]. Fluoride ion batteries can theoretically achieve a high-...
A VOx coating of Li1.2Mn0.56Ni0.16Co0.08O2, made through a low-temperature annealing process (350 °C), results in the formation of a protecting layer, which enables electrodes to be prepared with an aqueous binder, offering a significantly improved electrochemical performance. The comparison with uncoated electrodes demonstrates the significantly i...