Showing papers by "Joachim Mayer published in 2021"

Boron-Mediated Grain Boundary Engineering Enables Simultaneous Improvement of Thermoelectric and Mechanical Properties in N-Type Bi2Te3

Abstract: Powder metallurgy introduces small structures of high-density grain boundaries into Bi2 Te3 -based alloys, which promises to enhance their mechanical and thermoelectric performance. However, due to the strong donor-like effect induced by the increased surface, Te vacancies form in the powder-metallurgy process. Hence, the as-sintered n-type Bi2 Te3 -based alloys show a lower figure of merit (ZT) value than their p-type counterparts and the commercial zone-melted (ZM) ingots. Here, boron is added to one-step-sintered n-type Bi2 Te3 -based alloys to inhibit grain growth and to suppress the donor-like effect, simultaneously improving the mechanical and thermoelectric (TE) performance. Due to the alleviated donor-like effect and the carrier mobility maintained in our n-type Bi2 Te2.7 Se0.3 alloys upon the addition of boron, the maximum and average ZT values within 298-473 K can be enhanced to 1.03 and 0.91, respectively, which are even slightly higher than that of n-type ZM ingots. Moreover, the addition of boron greatly improves the mechanical strength such as Vickers hardness and compressive strength due to the synergetic effects of Hall-Petch grain-boundary strengthening and boron dispersion strengthening. This facile and cost-effective grain boundary engineering by adding boron facilitates the practical application of Bi2 Te3 -based alloys and can also be popularized in other thermoelectric materials.

In Situ Observation of Point-Defect-Induced Unit-Cell-Wise Energy Storage Pathway in Antiferroelectric PbZrO3

Abstract: Phase transition is established to govern electrostatic energy storage for antiferroelectric (AFE)-type dielectric capacitors. However, the source of inducing the phase transition and the pathway of storing the energy remains elusive so far given the ultrafast charging/discharging process under normal working conditions. Here, by slowing down the phase-transition speed using electronbeam irradiation as an external stimulus, the in situ dynamic energy-storage process in AFE PbZrO3 is captured by using atomic-resolution transmission electron microscopy. Specifically, it is found that oxygen-lead-vacancy-induced defect core acts as a seed to initiate the antiferrodistortive-to-ferrodistortive transition in antiparallel-Pb-based structural frames. Associated with polarity evolution of the compressively strained defect core, the ferroelectric (FE)– ferrodistortive state expands bilaterally along the b-axis direction and then develops into charged domain configurations during the energy-storage process, which is further evidenced by observations at the ordinary FE states. With filling the gap of perception, the findings here provide a straightforward approach of unveiling the unit-cell-wise energy storage pathway in chemical defect-engineered dielectric ceramics.

Flame synthesis of carbon metal-oxide nanocomposites in a counterflow burner

Abstract: Core-shell carbon metal-oxide nanocomposites are synthesized in a well-defined counterflow burner. Benefitting from the two-nozzle configuration, the nanocomposite morphology can be controlled by adjusting the precursor loading rate and fuel mass fraction independently. In-situ laser diagnostic method and transmission electron microscopy (TEM) technique are used to investigate the formation mechanism of nanocomposites. In the presence of a 532 nm laser pulse, laser-induced incandescence, Ti atomic emissions, and C2 swan spectra that appear simultaneously can indicate the particle volume fraction, titanium component, and carbon component, respectively. By increasing the precursor loading rates, both the measured laser diagnostic signals and the TEM images demonstrate that the titania component rises proportionally with the precursor concentration while the carbonaceous layer thickness remains unchanged. As further revealed by the axial profiles of the three signals, the formation and growth of the nanocomposites is composed of two steps. The first step is the reaction, nucleation, collision, and coagulation of metal oxides in the oxidizer side of the flame sheet. The second step is the formation of carbonaceous layers surrounding the metal oxides, which can be regarded as the heterogeneous nucleation of the carbonaceous species in the fuel-rich zone. By adjusting the precursor concentration and the fuel mass fraction, we can achieve independent control of the first and the second steps, respectively, thereby actively tailoring the core size of metal oxides and the carbonaceous layer thickness.

Multiple polarization orders in individual twinned colloidal nanocrystals of centrosymmetric HfO2

Abstract: Summary Spontaneous polarization is essential for ferroelectric functionality in non-centrosymmetric crystals. High-integration-density ferroelectric devices require the stabilization of polarization in small volumes. Here, atomic-resolution transmission electron microscopy imaging reveals that twinning gives rise to multiple polarization orders without symmetry breaking in colloidal nanocrystals of HfO2. The polarization orders are associated with sub-nanometer ferroelectric and antiferroelectric phases. The minimum size limit of the ferroelectric phase is found to be ∼4 nm3. Density functional theory calculations indicate that transformations between the ferroelectric and antiferroelectric phases are energetically possible. This work provides a route toward applications of HfO2 nanocrystals in information storage at densities that are more than an order of magnitude higher than the scaling limit defined by the nanocrystal size. Our results on the formation of twinning-induced polarization orders without symmetry breaking may provide general guidance for the discovery of new ferroelectric phases in ionic compounds that are not restricted to oxides.

Conditioning nano-LEDs in arrays by laser-micro-annealing: The key to their performance improvement

Abstract: A local so-called laser-micro-annealing (LMA) conditioning technology, which is suitable for the fabrication of a large range of hybrid nano-optoelectronic devices, was applied to III-nitride-based nano-light emitting diodes (LEDs). The LEDs with a diameter of ∼100 nm were fabricated in large area arrays and designed for hybrid optoelectronic applications. The LMA process was developed for the precise local conditioning of LED nano-structures. Photoluminescence measurements reveal the enhancement of nano-LED properties, which is in very good agreement with a simple model introduced based on the reduction of the defect layer depth by the LMA process. The experimental data confirm the reduction of the defect layer depth from ∼17 nm to ∼5 nm determined. In consequence, an increase in work currents up to 40 nA at 5 V bias after the LMA procedure as well as high electroluminescence (EL) and output optical power up to 150 nW in the ∼440–445 nm emission wavelength range corresponding to ∼75% wall-plug efficiency were achieved. Additionally, the LEDs' electroluminescence intensities reach the desired values by conditioning the contact/annealed regions of individual LEDs accordingly. Furthermore, the LMA process affects the long-term stability of the electroluminescence (EL) intensity of single nano-LED devices. A study of the EL during 5000 h in the continuous wave operation testing mode revealed a moderate ∼15% decrease in the intensity in comparison to ∼50% for their non-LMA counterparts. Finally, Raman measurements indicate that the “work” temperature for nano-LED conditioned structures decreases.

Ferroelectric phase-transition frustration near a tricritical composition point.

Abstract: Phase transition describes a mutational behavior of matter states at a critical transition temperature or external field. Despite the phase-transition orders are well sorted by classic thermodynamic theory, ambiguous situations interposed between the first- and second-order transitions were exposed one after another. Here, we report discovery of phase-transition frustration near a tricritical composition point in ferroelectric Pb(Zr1-xTix)O3. Our multi-scale transmission electron microscopy characterization reveals a number of geometrically frustrated microstructure features such as self-assembled hierarchical domain structure, degeneracy of mesoscale domain tetragonality and decoupled polarization-strain relationship. Associated with deviation from the classic mean-field theory, dielectric critical exponent anomalies and temperature dependent birefringence data unveil that the frustrated transition order stems from intricate competition of short-range polar orders and their decoupling to long-range lattice deformation. With supports from effective Hamiltonian Monte Carlo simulations, our findings point out a potentially universal mechanism to comprehend the abnormal critical phenomena occurring in phase-transition materials. Phase transition brings a plethora of exotic phenomena and intriguing effects such as spin and charge frustration. However, the phase transition order is not always explicit. Here, the authors discover phase transition frustration near a tricritical composition point in ferroelectric Pb(Zr,Ti)O3.

Enhancing the high temperature oxidation behavior of Cr2AlC coatings by reducing grain boundary nanoporosity

Abstract: The oxidation behavior of Cr2AlC MAX phase coatings with columnar and equiaxed morphologies is compared. After oxidation at 1100°C for 240 min the Cr2AlC MAX phase coatings with equiaxed grains sho...

Correlating Nanocrystalline Structure with Electronic Properties in 2D Platinum Diselenide

Abstract: Platinum diselenide (PtSe${_2}$) is a two-dimensional (2D) material with outstanding electronic and piezoresistive properties. The material can be grown at low temperatures in a scalable manner which makes it extremely appealing for many potential electronics, photonics, and sensing applications. Here, we investigate the nanocrystalline structure of different PtSe${_2}$ thin films grown by thermally assisted conversion (TAC) and correlate them with their electronic and piezoresistive properties. We use scanning transmission electron microscopy for structural analysis, X-ray photoelectron spectroscopy (XPS) for chemical analysis, and Raman spectroscopy for phase identification. Electronic devices are fabricated using transferred PtSe${_2}$ films for electrical characterization and piezoresistive gauge factor measurements. The variations of crystallite size and their orientations are found to have a strong correlation with the electronic and piezoresistive properties of the films, especially the sheet resistivity and the effective charge carrier mobility. Our findings may pave the way for tuning and optimizing the properties of TAC-grown PtSe${_2}$ towards numerous applications.

Turning Low-Nanoscale Intrinsic Silicon Highly Electron-Conductive by SiO2 Coating.

Abstract: Impurity doping in silicon (Si) ultra-large-scale integration is one of the key challenges which prevent further device miniaturization. Using ultraviolet photoelectron spectroscopy and X-ray absorption spectroscopy in the total fluorescence yield mode, we show that the lowest unoccupied and highest occupied electronic states of ≤3 nm thick SiO2-coated Si nanowells shift by up to 0.2 eV below the conduction band and ca. 0.7 eV below the valence band edge of bulk silicon, respectively. This nanoscale electronic structure shift induced by anions at surfaces (NESSIAS) provides the means for low-nanoscale intrinsic Si (i-Si) to be flooded by electrons from an external (bigger, metallic) reservoir, thereby getting highly electron- (n-) conductive. While our findings deviate from the behavior commonly believed to govern the properties of silicon nanowells, they are further confirmed by the fundamental energy gap as per nanowell thickness when compared against published experimental data. Supporting our findings further with hybrid density functional theory calculations, we show that other group IV semiconductors (diamond, Ge) do respond to the NESSIAS effect in accord with Si. We predict adequate nanowire cross-sections (X-sections) from experimental nanowell data with a recently established crystallographic analysis, paving the way to undoped ultrasmall silicon electronic devices with significantly reduced gate lengths, using complementary metal-oxide-semiconductor-compatible materials.

Local increase in compressive strain (GaN) in gate recessed AlGaN/GaN MISHFET structures induced by an amorphous AlN dielectric layer

Abstract: We fabricated and characterized metal insulator semiconductor (MIS) structures by applying amorphous AlN thin layers as a dielectric in gate recessed AlGaN/GaN heterostructure field effect transistors (HFETs). Micro photoluminescence measurements performed on MISHFET devices reveal a local non-uniform distribution of strain in the source—gate recess—drain region. Furthermore, a reduction of compressive stress up to 0.3 GPa in GaN after gate recessing was experimentally determined. The local stress increases by ∼0.1 GPa and ∼0.2 GPa after the deposition of 4 and 6 nm thin AlN layers in the gate recessed structures, respectively. Additionally, an increase in sheet charge density in the devices under investigation from ∼ 3.8×1012cm−2 to ∼ 6.2×1012cm−2 was evaluated by capacitance–voltage measurements. Therefore, strain engineering by applying amorphous AlN layers in gate recessed MISHFETs can significantly improve their device characteristics.

Nickel Structures as a Template Strategy to Create Shaped Iridium Electrocatalysts for Electrochemical Water Splitting.

Abstract: Low-cost, highly active, and highly stable catalysts are desired for the generation of hydrogen and oxygen using water electrolyzers. To enhance the kinetics of the oxygen evolution reaction in an acidic medium, it is of paramount importance to redesign iridium electrocatalysts into novel structures with organized morphology and high surface area. Here, we report on the designing of a well-defined and highly active hollow nanoframe based on iridium. The synthesis strategy was to control the shape of nickel nanostructures on which iridium nanoparticles will grow. After the growth of iridium on the surface, the next step was to etch the nickel core to form the NiIr hollow nanoframe. The etching procedure was found to be significant in controlling the hydroxide species on the iridium surface and by that affecting the performance. The catalytic performance of the NiIr hollow nanoframe was studied for oxygen evolution reaction and shows 29 times increased iridium mass activity compared to commercially available iridium-based catalysts. Our study provides novel insights to control the fabrication of iridium-shaped catalysts using 3d transition metal as a template and via a facile etching step to steer the formation of hydroxide species on the surface. These findings shall aid the community to finally create stable iridium alloys for polymer electrolyte membrane water electrolyzers, and the strategy is also useful for many other electrochemical devices such as batteries, fuel cells, sensors, and solar organic cells.

Phase Formation and Thermal Stability of Reactively Sputtered YTaO4-ZrO2 Coatings.

Abstract: Y(1-x)/2Ta(1-x)/2ZrxO2 coatings with 0 to 44 mol% ZrO2 were synthesized by sputtering Phase-pure M'-YTaO4 coatings were obtained at a substrate temperature of 900 °C Alloying with ZrO2 resulted in the growth of M' along with t-Zr(Y,Ta)O2 for ≤15 mol%, while for ≥28 mol%, ZrO2 X-ray diffraction (XRD) phase-pure metastable t was formed, which may be caused by small grain sizes and/or kinetic limitations The former phase region transformed into M' and M and the latter to an M' + t and M + t phase region upon annealing to 1300 and 1650 °C, respectively In addition to M and t, T-YTa(Zr)O4 phase fractions were observed at room temperature for ZrO2 contents ≥28 mol% after annealing to 1650 °C T phase fractions increased during in situ heating XRD at 80 °C At 1650 °C, a reaction with the α-Al2O3 substrate resulted in the formation of AlTaO4 and an Al-Ta-Y-O compound

Phase formation and performance of solid state reactive sintered Ce0.8Gd0.2O2−δ–FeCo2O4 composites

Abstract: Reactive sintering of dual phase composites for use as oxygen transport membranes is a promising method enabling lower sintering temperatures as well as low-cost raw materials. Ce0.8Gd0.2O2−δ–FeCo2O4 composites with different nominal weight ratios from 60 : 40 to 90 : 10 are processed by reactive sintering of commercial Ce0.8Gd0.2O2−δ, Fe2O3, and Co3O4 powders. The phases formed in situ during sintering are investigated qualitatively and quantitatively by means of XRD and Rietveld refinement as well as transmission electron microscopy. Besides gadolinia-doped ceria, two Fe/Co-spinel phases are in equilibrium in agreement with the phase diagram. Moreover, a donor-doped GdFeO3-based perovskite (Gd,Ce)(Fe,Co)O3 showing electronic conductivity is formed. Due to these intense phase reactions, the composition of each individual phase is assessed for all composites and their functional properties are discussed. The oxygen permeation performances of the composites are measured including their dependence on temperature and the potential limiting steps are discussed. The results reveal that the phase reactions support the formation of the desired mixed ionic electronic conductivity achieving percolation at low nominal spinel contents. The specific microstructure plays an extremely important role in the membrane performance and, thus, special attention should be paid to this in future research about dual phase membranes.

Influence of temperature on wear performance of greases in rolling bearings

Abstract: Rolling bearing operation under mixed and boundary lubrication conditions may lead to heavy adhesive or abrasive wear, which may lead to wear-induced rolling bearing failure. The purpose of this paper is to investigate the wear protection capabilities of different grease compositions at varying temperatures. It is considered that the temperature influences the lubrication conditions, the behaviour of grease components, namely, bleed oil and thickener, as well as the tribofilm formation due to tribo-chemical interactions between additives and surfaces.,In this study, four different greases were produced on the basis of a mineral base oil by varying the thickener and the addition of ZDDP. Various grease-lubricated rolling bearing experiments were conducted in a wide temperature range from 0°C to 120°C. Subsequently, the wear pattern, tribofilm formation and grease structures were analysed. Thereby, the influence of the different grease thickeners and the performance of ZDDP as a common antiwear and extreme pressure additive was evaluated.,The results show a strong temperature-dependency and allow a classification of temperature ranges concerning wear protection. At low temperatures, all greases provide a very good wear protection without the evidence of additive-based tribofilm formation. In the experiments at elevated temperatures, ZDDP tribofilms were formed. The formation depends on the thickener type: in comparison to lithium thickener, polyurea thickener favours more protective tribofilms at the same temperature. The experimental results show that medium temperatures in the range of 40°C–60°C are critical concerning wear due to the insufficient tribolayer formation and limited load carrying capacity of the grease.,Temperature is a key operating parameter for grease lubrication in roller bearings. The experimental work enables consideration of different impact pathways of temperature by combining roller bearing tests and microanalysis.

Ru Catalyst Encapsulated into the Pores of MIL-101 MOF: Direct Visualization by TEM.

Abstract: Ru catalyst nanoparticles were encapsulated into the pores of a Cr-based metal-organic framework (MOF)-MIL-101. The obtained material, as well as the non-loaded MIL-101, were investigated down to the atomic scale by annular dark-field scanning transmission electron microscopy using low dose conditions and fast image acquisition. The results directly show that the used wet chemistry loading approach is well-fitted for the accurate embedding of the individual catalyst nanoparticles into the cages of the MIL-101. The MIL-101 host material remains crystalline after the loading procedure, and the encapsulated Ru nanoparticles have a metallic nature. Annular dark field scanning transmission electron microscopy, combined with EDX mapping, is a perfect tool to directly characterize both the embedded nanoparticles and the loaded nanoscale MOFs. The resulting nanostructure of the material is promising because the Ru nanoparticles hosted in the MIL-101 pores are prevented from agglomeration-the stability and lifetime of the catalyst could be improved.

DNA introduces an independent temperature responsiveness to thermosensitive microgels and enables switchable plasmon coupling as well as controlled uptake and release

Abstract: A novel DNA-microgel hybrid system with dual thermal responsiveness is introduced uitilizing covalent coupling of single stranded DNA (ssDNA) to thermoresponsive microgels (μGs). The spatial distribution of the coupling sites for the ssDNA was characterized with 3D superresolution fluorescence microscopy. The DNA-functionalized μGs remain thermoresponsive and can take up dye-labeled complementary ssDNA, which can be released again by overcoming the dehybridization temperature of the DNA independently of the volume phase transition (VPT) of the μGs. The same holds for nano-objects represented by plasmonic gold nanoparticles (AuNPs), the penetration depth of which was visualized via TEM tomography and 3D reconstruction and which show enhanced plasmonic coupling in the collapsed state of the μG and thus gets switchable. In contrast, if ssDNA was taken up just by non-specific interactions, i.e. into non-functionalized μGs, its release is temperature-independent and can only be induced by increasing the salt concentration. Thus, the incorporated ssDNA represents highly selectice binding sites determined by their base number and sequence, which makes the VPT, beeing determined by the μG composition, and the reversible uptake and release enabled through programmable DNA hybridization are independent features. The combination with the typically high biocompatibility and the retained swellability and permeability hold promise for new fundamental insights as well as for potential applications in biological environments.

Migration Kinetics of Surface Ions in Oxygen-Deficient Perovskite During Topotactic Transitions.

Abstract: Oxygen diffusivity and surface exchange kinetics underpin the ionic, electronic, and catalytic functionalities of complex multivalent oxides. Towards understanding and controlling the kinetics of oxygen transport in emerging technologies, it is highly desirable to reveal the underlying lattice dynamics and ionic activities related to oxygen variation. In this study, the evolution of oxygen content is identified in real-time during the progress of a topotactic phase transition in La0.7 Sr0.3 MnO3-δ epitaxial thin films, both at the surface and throughout the bulk. Using polarized neutron reflectometry, a quantitative depth profile of the oxygen content gradient is achieved, which, alongside atomic-resolution scanning transmission electron microscopy, uniquely reveals the formation of a novel structural phase near the surface. Surface-sensitive X-ray spectroscopies further confirm a significant change of the electronic structure accompanying the transition. The anisotropic features of this novel phase enable a distinct oxygen diffusion pathway in contrast to conventional observation of oxygen motion at moderate temperatures. The results provide insights furthering the design of solid oxygen ion conductors within the framework of topotactic phase transitions.

Novel realization of superconducting topological-insulator nanowires

Abstract: When a topological insulator (TI) is made into a nanowire, the interplay between topology and size quantization gives rise to peculiar one-dimensional (1D) states whose energy dispersion can be manipulated by external fields. With proximity-induced superconductivity, these 1D states offer a tunable platform for Majorana zero modes (MZMs) that can be robust even in the presence of disorder. While the realization of the peculiar 1D states was recently confirmed, realization of robust proximity-induced superconductivity in TI nanowires remains a challenge. Here we report novel realization of superconducting TI nanowires based on (Bi$_{1-x}$Sb$_x$)$_2$Te$_3$ (BST) thin films: When two rectangular pads of Pd are deposited on a BST thin film with a separation of 100 - 200 nm, the BST beneath the pads is converted into a superconductor, leaving a nanowire of BST in-between. We found that the interface is "epitaxial" and has a high electronic transparency, leading to a robust superconductivity induced in the BST nanowire. Due to its suitable geometry for gate-tuning, this new platform is promising for future studies of MZMs.

Photocatalytic-Fenton Process under Simulated Solar Radiation Promoted by a Suitable Catalyst Selection

Abstract: Considering water scarcity, photo-based processes have been presented as a depollution technique, which should be optimized in order to be applied in the future. For that, the addition of an active photocatalyst and the usage of solar radiation are mandatory steps. Thus, Fe3O4–SiO2–TiO2 was synthesized, and its performance was evaluated using simulated solar radiation and methylene blue as a model pollutant. Under optimal conditions, 86% degradation was attained in 1 h. These results were compared to recent published data, and the better performance can be attributed to both the operational conditions selection and the higher photocatalyst activity. Indeed, Fe3O4–SiO2–TiO2 was physico-chemically characterized with techniques such as XRD, N2 isotherms, spectrophotometry, FTIR, electrochemical assays and TEM.

Elucidating the Influence of the d-Band Center on the Synthesis of Isobutanol

Abstract: As the search for carbon-efficient synthesis pathways for green alternatives to fossil fuels continues, an expanding class of catalysts have been developed for the upgrading of lower alcohols. Understanding of the acid base functionalities has greatly influenced the search for new materials, but the influence of the metal used in catalysts cannot be explained in a broader sense. We address this herein and correlate our findings with the most fundamental understanding of chemistry to date by applying it to d-band theory as part of an experimental investigation. The commercial catalysts of Pt, Rh, Ru, Cu, Pd, and Ir on carbon as a support have been characterized by means of SEM, EDX-mapping, STEM, XRD, N2-physisorption, and H2-chemisorption. Their catalytic activity has been established by means of c-methylation of ethanol with methanol. For all catalysts, the TOF with respect to i-butanol was examined. The Pt/C reached the highest TOF with a selectivity towards i-butanol of 89%. The trend for the TOFs could be well correlated with the d-band centers of the metal, which formed a volcano curve. Therefore, this study is another step towards the rationalization of catalyst design for the upgrading of alcohols into carbon-neutral fuels or chemical feedstock.

Co-Deformation of the Metallic Matrix and Intermetallic Phases in an Mg-3.68Al-3.8Ca Alloy

Abstract: Mg-Al-Ca alloys are well-known for their excellent creep resistance at elevated temperatures (≤ 200 °C). In the present study, the deformation behaviour of an Mg-3.68Al-3.8Ca alloy containing a network composed of an α-Mg phase matrix and an intragranular eutectic Laves phase network was studied within the temperature range of 20-170 °C using (instrumented) indentation at constant and variable strain rate including creep (relaxation) tests in combination with SEM, TEM and AFM. The geometry of the deformation zone around and below microindents was found to be orientation-dependent and influenced by the presence of Laves phases. The Laves phase was found to exhibit slip lines at intersections with slip lines and twins in the α-Mg phase. In addition to basal slip, non-basal slip was also observed in the α-Mg matrix (especially at α-Mg/Laves phase interfaces) along with basal slip in the Laves phase as confirmed by post-mortem TEM. The strain rate sensitivity, m, of the softer α-Mg phase and the interfaces was observed to increase with temperature. The nanoindentation creep tests showed that the creep properties of the Mg2Ca Laves phase are much better than those of the α-Mg phase. However, creep tests on interfaces indicated deformation by interfacial sliding and revealed creep properties similar to those of the α-Mg phase.

Temperature dependent partitioning mechanisms and its associated microstructural evolution in a CMnSiAl quenching and partitioning (Q&P) steel

Abstract: The effect of temperature (350 °C i M S i 450 °C) on the partitioning mechanisms and the final microstructure evolution in a CMnSiAl quenching and partitioning (Q&P) steel was investigated. The microstructure of both the Q&P specimens, comprised of distorted BCC or pseudo tetragonal martensite structure with two different characteristics namely (i) tempered or carbon depleted martensite that formed during initial quenching (M f i 240 °C i M S ) and partitioning step and (ii) carbon enriched fresh martensite that formed after partitioning step and final quenching (RT) together with blocky and inter-lath films of retained austenite. In addition, packets of M/A constituents were observed in Q&P-350-1min specimen and some traces of carbide and plate martensite were observed in Q&P-450-1min specimen. The increase in partitioning temperature led to nearly 2% increase in the amount of retained austenite (both blocky and inter-lath) with increased carbon content of 0.27 wt.%. Along with carbon partitioning, slight interface mobility/isothermal martensite formation was also observed in the case of specimen partitioned at 350 °C, whereas tempering effect was predominantly seen in the case of specimen partitioned at 450 °C. Irrespective of the partitioning temperature, the amount of carbon required to stabilize the retained austenite at RT was found to be about 1.15 wt.% and was confirmed through APT analysis.