The interplay between thermodynamics and kinetics in the solid-state synthesis of layered oxides

Abstract

In the synthesis of inorganic materials, reactions often yield non-equilibrium kinetic byproducts instead of the thermodynamic equilibrium phase. Understanding the competition between thermodynamics and kinetics is fundamental towards the rational synthesis of target materials. Here, we use in situ synchrotron X-ray diffraction to investigate the multistage crystallization pathways of the important two-layer (P2) sodium oxides Na 0.67 MO 2 (M = Co, Mn). We observe a series of fast non-equilibrium phase transformations through metastable three-layer O3, O3' and P3 phases before formation of the equilibrium two-layer P2 polymorph. We present a theoretical framework to rationalize the observed phase progression, demonstrating that even though P2 is the equilibrium phase, compositionally-unconstrained reactions between powder precursors favor the formation of non-equilibrium three-layered intermediates. These insights can guide the choice of precursors and parameters employed in the solidstate synthesis of ceramic materials, and constitutes a step forward in unraveling the complex interplay between thermodynamics and kinetics during materials synthesis.

Anionic Redox Reactions in Cathodes for Sodium‐Ion Batteries

“…In these structures, “P” or “O” indicates prismatic or octahedral coordination, respectively, for Na + , and “2” or “3” represents the number of TM layers with different types of oxygen stacking in a single unit cell [61,67] . Because of the large ionic radius of the Na + ion, both octahedral and prismatic coordination is possible; thus, the most common structures are P2, P3, O2, and O3 in layered sodium TMOs [28] …”

Probing the charged state of layered positive electrodes in sodium-ion batteries: reaction pathways, stability and opportunities

“…7. 16 Similar to P2 and O3-type phases, doping may also help to improve the performance of P3-type layered oxides. For example, Wang et al found that substitution of a small quantity of oxygen for uorine to form Na 0.65 Mn 0.75 -Ni 0.25 F 0.1 O 1.9 could suppress the P3-O1 transition.…”

Mechanistic insight of KBiQ2 (Q = S, Se) using panoramic synthesis towards synthesis-by-design

“…The reaction selectivity of K 3 BiQ 3 (Q = S, Se) directly proceeding the formation of the KBiQ 2 ternary is postulated to be structural in origin as opposed to energetic. In-situ studies observing the phase formation found the composition of the first transient phase to be that which yielded the largest energy release 81 or the fastest energy release 30 . The former does not apply for these chalcogenide systems as the formation of K 3 BiQ 3 is less energetically favorable than the β- In order to isolate α-KBiSe 2 , the product was quenched at 650°C and annealed.…”