SANJIT GHOSE

Reactive flash sintering (RFS) enables the simultaneous synthesis and sintering of ceramics and has been shown to affect the reaction pathway of different materials. Herein, in situ synchrotron X‐ray diffraction (XRD) is used to investigate the (Mg,Ni,Co,Cu,Zn)O entropy‐stabilized oxide formation during: (i) conventional heating and (ii) RFS under current rate‐controlled mode. The same reaction pathway is verified in both instances: the starting rock‐salt (RS), spinel (Co₃O₄), tenorite (CuO), and wurtzite (ZnO) phases transform into a single RS phase with a (1 1 1) to (2 0 0) intensity ratio of 0.67, consistent with a random distribution of the cations into the structure. Pt lattice peak shift from the XRD patterns is used as standard to monitor the sample surface temperature, revealing a strong endothermic reaction during the RS single‐phase formation (Pt peaks shift toward higher angles while increasing sample temperature/current density). In RFS, the single‐phase RS structure is formed in just 60 s at a furnace temperature of 600°C and a current rate of 220 mA mm⁻²/min. Therefore, RFS greatly accelerates the synthesis of (Mg,Ni,Co,Cu,Zn)O, however, it does not play a role in the reaction pathway for this material formation.

In situ X-ray scattering measurements of CsPbX ₃ (X = Cl, Br, I) nanocrystal formation and halide exchange at NSLS-II beamlines were performed in an automated flow reactor. Total scattering measurements were performed at the 28-ID-2 (XPD) beamline and small-angle X-ray scattering at the 16-ID (LiX) beamline. Nanocrystal structural parameters of interest, including size, size distribution and atomic structure, were extracted from modeling the total scattering data. The results highlight the potential of these beamlines and the measurement protocols described in this study for studying dynamic processes of colloidal nanocrystal synthesis in solution with timescales on the order of seconds.

Sulfur is a promising cathode material for rechargeable lithium batteries due to its high capacity, low cost, abundance, and high sustainability. However, lithium sulfur batteries suffer from poor cycle life and low energy density under lean electrolyte conditions because of the dissolution of lithium polysulfide intermediates. Here, we report that the chemical bonding between sulfur and carbon/oxygen in an oxygen-rich dense carbon host can stabilize sulfur and improve the stability of lean electrolyte lithium sulfur batteries. This work opens up a way to develop chemical bonding-stabilized sulfur materials for stable and high-energy lithium sulfur batteries.

There is growing evidence that oxides of complex chemistries can be formed in one step by reactive flash sintering of their elemental constituents. Here we explore the temporal relationship between phase transformation and sintering by combining measurements of sintering with in situ measurements of phase transformation. The experiments are carried out under current rate, where flash is induced by injecting current and increasing it at a constant rate. We show that phase transformation of powders of magnesia and α‐alumina into single‐phase magnesium aluminate spinel was completed in 45 seconds, whereas sintering to full density required 60 seconds.

We show that flash experiments with three phase mixed‐powders of yttria‐stabilized zirconia (8YSZ), MgO, and α‐Al₂O₃ not only produce polycrystals of high density, but also the transformation of magnesia and alumina into single‐phase spinel. The presence of zirconia facilitates the onset of the flash. The sintering experiments in the laboratory were extended to live experiments at the National Synchrotron Light Source II at Brookhaven National Laboratory in order to measure the time‐dependent evolution of single‐phase spinel. The phase transformation occurred in <3 seconds during Stage II. Later, during Stage III the cubic zirconia transformed partly into the monoclinic phase, which reverted back to the cubic phase when the flash was extinguished by turning off the current to the specimen. The results underpin a recent report on the synthesis of single‐phase bismuth ferrite from constituent oxides in reactive flash experiments, raising the specter of flash as a method for synthesis as well as sintering of complex oxide ceramics. The role of zirconia in catalyzing the flash in the present study is discussed.

During synthesis, Zn²⁺ ions become coordinated by 2-methylimidazole to form secondary building units which function as building blocks to the final ZIF-8 framework.