Madhav Reddy - Academia.edu (original) (raw)
Papers by Madhav Reddy
Materials Horizons
This work demonstrates a green-solvent-processed FA-based perovskite film based on a SnO2-NR subs... more This work demonstrates a green-solvent-processed FA-based perovskite film based on a SnO2-NR substrate with Cl-terminated bifunctional supramolecule passivation and has achieved a highest PCE of 22.42% with long-term stability.
Journal of Materials Science & Technology, 2021
Aging treatment of Cu-based alloys is essential to enhance their strength that is desirable for t... more Aging treatment of Cu-based alloys is essential to enhance their strength that is desirable for their extensive engineering applications in electrical industry, whereas the underlying mechanism of strengthening is essential for massive manufacturing of these alloys. Here, the microstructure evolution of a supersaturated solid solution Cu-15Ni-8Sn-0.2Nb alloy aged at 400 °C for different time was characterized at atomic scale using state-of-the-art transmission electron microscopy (TEM) and the corresponding mechanical property was also measured. The results reveal that the modulated structure, DO22/L12 ordering, and discontinuous precipitation (DP) appeared in the advances of aging time. At the early stage of aging treatment, component modulation waves and satellite spots appeared from spinodal decomposition and the modulation wavelength was identified in the range of 1–7 nm. Subsequently the modulated structures formed -poor-rich solute regions, of which DO22 ordering was present i...
Materials Characterization, 2020
Microstructure and mechanical properties of δ-TRIP C-Mn-Al-Si steels without and with 0.03 (wt)% ... more Microstructure and mechanical properties of δ-TRIP C-Mn-Al-Si steels without and with 0.03 (wt)% Nb and 0.05 (wt)% Ti addition were studied. Tensile tests show the excellent combination of the yield strength and total elongation of the Nb and Ti microalloyed δ-TRIP steel, and the product of strength and elongation is 31.59 GPa•%, which is obviously superior than that of pristine δ-TRIP steel. Microstructure characterization shows that the addition of trace Nb and Ti effectively refines original austenite grain size. The high density of nano-sized (Nb, Ti)C precipitates as a significant contribution on the pinning effect on dislocations improve the strength of the microalloyed δ-TRIP steel. In addition, the effect of Nb and Ti on the microstructural evolution and deformation mechanism of the δ-TRIP steel was discussed.
Materials Characterization, 2021
Abstract Boron carbide (B4C) often consists of intrinsic secondary phase precipitates that are fo... more Abstract Boron carbide (B4C) often consists of intrinsic secondary phase precipitates that are formed during the reaction-sintering process. These precipitates not only play an important role during the densification process but also affect the mechanical properties of B4C. In the present study, the structural determination of multicomponent secondary phases that are precipitated out in monolithic B4C was investigated using atomic resolution scanning transmission electron microscopy (STEM) and atom probe tomography (APT). Here we found two types (Type-I and II) of multicomponent boride nano-precipitates in B4C i.e. (i) elongated precipitates (type-I), identified as (Cr(1-x-y)-Fex-Wy)3B4 phase, rich in chromium (Cr), Iron (Fe), tungsten (W), and boron (B) (ii) equiaxial (type-II) precipitates that are rich in titanium (Ti), Cr, and B in form of Ti(1-x)CrxB2 phase. The estimated reduced modulus and hardness using depth sensitive nanoindentation on type-I precipitates were 335 ± 6 GPa and 32 ± 2 GPa and that in type-II precipitates were 268 ± 13 GPa and 22 ± 3 GPa, respectively. These results underscore the importance of multicomponent solid solution hardening in ultra-hard B4C material.
Materials Today Energy, 2021
Abstract Two-dimensional chromium carbide-based MXenes are predicted as an efficient catalyst for... more Abstract Two-dimensional chromium carbide-based MXenes are predicted as an efficient catalyst for the hydrogen evolution reaction (HER). However, the lack of an effective approach to fabricate this promising material remains an impediment to practical applications. Herein, a simple strategy is proposed to synthesis Cr 2CTx ultrathin structures from Cr2 AlC MAX. The high-resolution analytical scanning transmission electron microscopy (STEM) corroborated with X-ray diffraction and scanning electron microscopy demonstrates that the Al atomic layers have been detached from the pristine MAX structure. Further atomic-resolution STEM confirms that the ultrathin Cr 2CTx sheets with fluoride-free surface, nanostructured Cr2CO2, and Al2O3 phases are originated as by-products. The electrochemical test shows that the fabricated Cr2CTx composite with minimal Al2O3 have a good performance for hydrogen evolution reaction and exceed even that of Pt sheet catalyst at high current density. Moreover, high stability of more than 160 h without attenuation was observed to be better than the other MXenes catalytic performer to date. This work paves a gentle route to fabricate Cr2CTx MXene and demonstrates the potential application for HER.
Journal of Materials Chemistry A, 2021
A surface treatment of PEDOT:PSS layer with [PNA]BF4 is employed to realize vertically homogeneou... more A surface treatment of PEDOT:PSS layer with [PNA]BF4 is employed to realize vertically homogeneous distribution of Sn/Pb-containing perovskite films through balancing its crystallization rate and achieving chemical encapsulation of the acidic PEDOT:PSS substrate.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2018
We report the fabrication of nanoporous silica coatings with tunable refractive indices by a one-... more We report the fabrication of nanoporous silica coatings with tunable refractive indices by a one-step basecatalyzed sol-gel process using tetraethoxysilane as the precursor, hexamethylisilazane as the modifier at ambient conditions. The advantages of the present method are inexpensive, etchant-free and without high temperature calcination treatment. Importantly, porosity of the coatings can be tunable by changing the monomer ratio of the starting solution, which makes them suitable for top layer of broadband AR coatings. The tri-wavelength broadband AR coating with the refractive indices of the bottom and top layers as 1.27 and 1.16 was achieved on a fused silica substrate, which possessed high transmittance of 99.6%, 98.0% and 99.3% at 351 nm, 527 nm and 1053 nm, respectively. Moreover, the double-layer coating showed significant stability, when tested with polydimethylsiloxane pollution in vacuum for a week. In addition, LIDT of the double-layer coating was up to ca. 19.0 J cm −2 at a 6.3 ns laser pulse of 351 nm wavelength. This double-layer AR coating possesses excellent broadband AR performance, high LIDT, and excellent vacuum stability, which can open a new avenue to explore applications in high-power laser systems.
Small, 2021
Single-atom cobalt-based CoNC are promising low-cost electrocatalysts for oxygen reduction reac... more Single-atom cobalt-based CoNC are promising low-cost electrocatalysts for oxygen reduction reaction (ORR). However, further increasing the single cobalt-based active sites and the ORR activity remain a major challenge. Herein, an acetate (OAc) assisted metal-organic framework (MOF) structure-engineering strategy is developed to synthesize hierarchical accordion-like MOF with higher loading amount and better spatial isolation of Co and much higher yield when compared with widely reported polyhedron MOF. After pyrolysis, the accordion-structured CoNC (CoNC (A)) is loaded with denser CoN4 active sites (Co: 2.88 wt%), approximately twice that of Co in the CoNC reported. The presence of OAc in MOF also induces the generation of big pores (5-50 nm) for improving the accessibility of active sites and mass transfer during catalytic reactions. Consequently, the CoNC (A) catalyst shows an admirable ORR activity with a E1/2 of 0.89 V (40 mV better than Pt/C) in alkaline electrolytes, outstanding durability, and absolute tolerance to methanol in both alkaline and acidic media. The CoNC-based Zn-air battery exhibits a high specific capacity (976 mAh g-1 Zn ), power density (158 mW cm-2 ), rate capability, and long-term stability. This work demonstrates a reliable approach to construct single atom doped carbon catalysts with denser accessible active sites through MOF structure engineering.
Materials Research Letters, 2018
We report the atomic structure of coincident stacking faults (SFs) in superhard boron suboxide (B... more We report the atomic structure of coincident stacking faults (SFs) in superhard boron suboxide (B 6 O) by combining annular bright field scanning transmission electron microscopy and quantum mechanics (QM) simulations. Different from simple SFs, which only lead to the symmetry breaking, the coincident SF junctions in the complex B 6 O result in local chemical configuration changes by forming an abnormal three-oxygen-atoms chain linking boron icosahedra, instead of the regular two-oxygen-atoms chain in a perfect B 6 O crystal. QM studies demonstrate that coincident SFs lead to the decreased shear strength under pure shear and indentation conditions and are responsible to the initial failure and amorphization of B 6 O. IMPACT STATEMENT Combining ABF-STEM and MD simulations, we demonstrated that the coincident SFs lead to the decrease of shear strength and are responsible for the initial failure and amorphization of B 6 O.
Nanoscale, 2021
Important progress is reported in the development of dual single-atom transition metal co-anchore... more Important progress is reported in the development of dual single-atom transition metal co-anchored catalysts, CuNx and NiNx moieties anchored on 3D nanoporous graphene, with superior ORR activities and durability for zinc–air batteries.
Scripta Materialia, 2010
... Permissions & Reprints. Innovative multi-stage spark plasma sintering to obtain strong an... more ... Permissions & Reprints. Innovative multi-stage spark plasma sintering to obtain strong and tough ultrafine-grained ceramics. K. Madhav Reddy a , Nitish Kumar a and Bikramjit Basu Corresponding Author Contact Information , a , E-mail The Corresponding Author. ...
Journal of Alloys and Compounds
Science Advances
The failure of superhard materials is often associated with stress-induced amorphization. However... more The failure of superhard materials is often associated with stress-induced amorphization. However, the underlying mechanisms of the structural evolution remain largely unknown. Here, we report the experimental measurements of the onset of shear amorphization in single-crystal boron carbide by nanoindentation and transmission electron microscopy. We verified that rate-dependent loading discontinuity, i.e., pop-in, in nanoindentation load-displacement curves results from the formation of nanosized amorphous bands via shear amorphization. Stochastic analysis of the pop-in events reveals an exceptionally small activation volume, slow nucleation rate, and lower activation energy of the shear amorphization, suggesting that the high-pressure structural transition is activated and initiated by dislocation nucleation. This dislocation-mediated amorphization has important implications in understanding the failure mechanisms of superhard materials at stresses far below their theoretical streng...
Journal of Materials Science & Technology
Materials Characterization
Metallurgical and Materials Transactions A
Journal of Alloys and Compounds
Materials Horizons
This work demonstrates a green-solvent-processed FA-based perovskite film based on a SnO2-NR subs... more This work demonstrates a green-solvent-processed FA-based perovskite film based on a SnO2-NR substrate with Cl-terminated bifunctional supramolecule passivation and has achieved a highest PCE of 22.42% with long-term stability.
Journal of Materials Science & Technology, 2021
Aging treatment of Cu-based alloys is essential to enhance their strength that is desirable for t... more Aging treatment of Cu-based alloys is essential to enhance their strength that is desirable for their extensive engineering applications in electrical industry, whereas the underlying mechanism of strengthening is essential for massive manufacturing of these alloys. Here, the microstructure evolution of a supersaturated solid solution Cu-15Ni-8Sn-0.2Nb alloy aged at 400 °C for different time was characterized at atomic scale using state-of-the-art transmission electron microscopy (TEM) and the corresponding mechanical property was also measured. The results reveal that the modulated structure, DO22/L12 ordering, and discontinuous precipitation (DP) appeared in the advances of aging time. At the early stage of aging treatment, component modulation waves and satellite spots appeared from spinodal decomposition and the modulation wavelength was identified in the range of 1–7 nm. Subsequently the modulated structures formed -poor-rich solute regions, of which DO22 ordering was present i...
Materials Characterization, 2020
Microstructure and mechanical properties of δ-TRIP C-Mn-Al-Si steels without and with 0.03 (wt)% ... more Microstructure and mechanical properties of δ-TRIP C-Mn-Al-Si steels without and with 0.03 (wt)% Nb and 0.05 (wt)% Ti addition were studied. Tensile tests show the excellent combination of the yield strength and total elongation of the Nb and Ti microalloyed δ-TRIP steel, and the product of strength and elongation is 31.59 GPa•%, which is obviously superior than that of pristine δ-TRIP steel. Microstructure characterization shows that the addition of trace Nb and Ti effectively refines original austenite grain size. The high density of nano-sized (Nb, Ti)C precipitates as a significant contribution on the pinning effect on dislocations improve the strength of the microalloyed δ-TRIP steel. In addition, the effect of Nb and Ti on the microstructural evolution and deformation mechanism of the δ-TRIP steel was discussed.
Materials Characterization, 2021
Abstract Boron carbide (B4C) often consists of intrinsic secondary phase precipitates that are fo... more Abstract Boron carbide (B4C) often consists of intrinsic secondary phase precipitates that are formed during the reaction-sintering process. These precipitates not only play an important role during the densification process but also affect the mechanical properties of B4C. In the present study, the structural determination of multicomponent secondary phases that are precipitated out in monolithic B4C was investigated using atomic resolution scanning transmission electron microscopy (STEM) and atom probe tomography (APT). Here we found two types (Type-I and II) of multicomponent boride nano-precipitates in B4C i.e. (i) elongated precipitates (type-I), identified as (Cr(1-x-y)-Fex-Wy)3B4 phase, rich in chromium (Cr), Iron (Fe), tungsten (W), and boron (B) (ii) equiaxial (type-II) precipitates that are rich in titanium (Ti), Cr, and B in form of Ti(1-x)CrxB2 phase. The estimated reduced modulus and hardness using depth sensitive nanoindentation on type-I precipitates were 335 ± 6 GPa and 32 ± 2 GPa and that in type-II precipitates were 268 ± 13 GPa and 22 ± 3 GPa, respectively. These results underscore the importance of multicomponent solid solution hardening in ultra-hard B4C material.
Materials Today Energy, 2021
Abstract Two-dimensional chromium carbide-based MXenes are predicted as an efficient catalyst for... more Abstract Two-dimensional chromium carbide-based MXenes are predicted as an efficient catalyst for the hydrogen evolution reaction (HER). However, the lack of an effective approach to fabricate this promising material remains an impediment to practical applications. Herein, a simple strategy is proposed to synthesis Cr 2CTx ultrathin structures from Cr2 AlC MAX. The high-resolution analytical scanning transmission electron microscopy (STEM) corroborated with X-ray diffraction and scanning electron microscopy demonstrates that the Al atomic layers have been detached from the pristine MAX structure. Further atomic-resolution STEM confirms that the ultrathin Cr 2CTx sheets with fluoride-free surface, nanostructured Cr2CO2, and Al2O3 phases are originated as by-products. The electrochemical test shows that the fabricated Cr2CTx composite with minimal Al2O3 have a good performance for hydrogen evolution reaction and exceed even that of Pt sheet catalyst at high current density. Moreover, high stability of more than 160 h without attenuation was observed to be better than the other MXenes catalytic performer to date. This work paves a gentle route to fabricate Cr2CTx MXene and demonstrates the potential application for HER.
Journal of Materials Chemistry A, 2021
A surface treatment of PEDOT:PSS layer with [PNA]BF4 is employed to realize vertically homogeneou... more A surface treatment of PEDOT:PSS layer with [PNA]BF4 is employed to realize vertically homogeneous distribution of Sn/Pb-containing perovskite films through balancing its crystallization rate and achieving chemical encapsulation of the acidic PEDOT:PSS substrate.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2018
We report the fabrication of nanoporous silica coatings with tunable refractive indices by a one-... more We report the fabrication of nanoporous silica coatings with tunable refractive indices by a one-step basecatalyzed sol-gel process using tetraethoxysilane as the precursor, hexamethylisilazane as the modifier at ambient conditions. The advantages of the present method are inexpensive, etchant-free and without high temperature calcination treatment. Importantly, porosity of the coatings can be tunable by changing the monomer ratio of the starting solution, which makes them suitable for top layer of broadband AR coatings. The tri-wavelength broadband AR coating with the refractive indices of the bottom and top layers as 1.27 and 1.16 was achieved on a fused silica substrate, which possessed high transmittance of 99.6%, 98.0% and 99.3% at 351 nm, 527 nm and 1053 nm, respectively. Moreover, the double-layer coating showed significant stability, when tested with polydimethylsiloxane pollution in vacuum for a week. In addition, LIDT of the double-layer coating was up to ca. 19.0 J cm −2 at a 6.3 ns laser pulse of 351 nm wavelength. This double-layer AR coating possesses excellent broadband AR performance, high LIDT, and excellent vacuum stability, which can open a new avenue to explore applications in high-power laser systems.
Small, 2021
Single-atom cobalt-based CoNC are promising low-cost electrocatalysts for oxygen reduction reac... more Single-atom cobalt-based CoNC are promising low-cost electrocatalysts for oxygen reduction reaction (ORR). However, further increasing the single cobalt-based active sites and the ORR activity remain a major challenge. Herein, an acetate (OAc) assisted metal-organic framework (MOF) structure-engineering strategy is developed to synthesize hierarchical accordion-like MOF with higher loading amount and better spatial isolation of Co and much higher yield when compared with widely reported polyhedron MOF. After pyrolysis, the accordion-structured CoNC (CoNC (A)) is loaded with denser CoN4 active sites (Co: 2.88 wt%), approximately twice that of Co in the CoNC reported. The presence of OAc in MOF also induces the generation of big pores (5-50 nm) for improving the accessibility of active sites and mass transfer during catalytic reactions. Consequently, the CoNC (A) catalyst shows an admirable ORR activity with a E1/2 of 0.89 V (40 mV better than Pt/C) in alkaline electrolytes, outstanding durability, and absolute tolerance to methanol in both alkaline and acidic media. The CoNC-based Zn-air battery exhibits a high specific capacity (976 mAh g-1 Zn ), power density (158 mW cm-2 ), rate capability, and long-term stability. This work demonstrates a reliable approach to construct single atom doped carbon catalysts with denser accessible active sites through MOF structure engineering.
Materials Research Letters, 2018
We report the atomic structure of coincident stacking faults (SFs) in superhard boron suboxide (B... more We report the atomic structure of coincident stacking faults (SFs) in superhard boron suboxide (B 6 O) by combining annular bright field scanning transmission electron microscopy and quantum mechanics (QM) simulations. Different from simple SFs, which only lead to the symmetry breaking, the coincident SF junctions in the complex B 6 O result in local chemical configuration changes by forming an abnormal three-oxygen-atoms chain linking boron icosahedra, instead of the regular two-oxygen-atoms chain in a perfect B 6 O crystal. QM studies demonstrate that coincident SFs lead to the decreased shear strength under pure shear and indentation conditions and are responsible to the initial failure and amorphization of B 6 O. IMPACT STATEMENT Combining ABF-STEM and MD simulations, we demonstrated that the coincident SFs lead to the decrease of shear strength and are responsible for the initial failure and amorphization of B 6 O.
Nanoscale, 2021
Important progress is reported in the development of dual single-atom transition metal co-anchore... more Important progress is reported in the development of dual single-atom transition metal co-anchored catalysts, CuNx and NiNx moieties anchored on 3D nanoporous graphene, with superior ORR activities and durability for zinc–air batteries.
Scripta Materialia, 2010
... Permissions & Reprints. Innovative multi-stage spark plasma sintering to obtain strong an... more ... Permissions & Reprints. Innovative multi-stage spark plasma sintering to obtain strong and tough ultrafine-grained ceramics. K. Madhav Reddy a , Nitish Kumar a and Bikramjit Basu Corresponding Author Contact Information , a , E-mail The Corresponding Author. ...
Journal of Alloys and Compounds
Science Advances
The failure of superhard materials is often associated with stress-induced amorphization. However... more The failure of superhard materials is often associated with stress-induced amorphization. However, the underlying mechanisms of the structural evolution remain largely unknown. Here, we report the experimental measurements of the onset of shear amorphization in single-crystal boron carbide by nanoindentation and transmission electron microscopy. We verified that rate-dependent loading discontinuity, i.e., pop-in, in nanoindentation load-displacement curves results from the formation of nanosized amorphous bands via shear amorphization. Stochastic analysis of the pop-in events reveals an exceptionally small activation volume, slow nucleation rate, and lower activation energy of the shear amorphization, suggesting that the high-pressure structural transition is activated and initiated by dislocation nucleation. This dislocation-mediated amorphization has important implications in understanding the failure mechanisms of superhard materials at stresses far below their theoretical streng...
Journal of Materials Science & Technology
Materials Characterization
Metallurgical and Materials Transactions A
Journal of Alloys and Compounds