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arxiv: 2604.24941 · v1 · submitted 2026-04-27 · ❄️ cond-mat.mtrl-sci

Visualizing Crystallization Dynamics and Transformation Pathways of Disordered Rocksalt Oxides During Thermally Activated Sol-Gel Synthesis

Diyi Cheng , Tim Kodalle , Anika T. Promi , Ansuman Halder , Raphael F. Moral , Madeline Grass , Venkata S. Avvaru , Haegyeom Kim
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Carolin M. Sutter-Fella Haimei Zheng
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Pith reviewed 2026-05-08 02:45 UTC · model grok-4.3

classification ❄️ cond-mat.mtrl-sci
keywords sol-gel synthesisdisordered rocksaltcrystallization pathwaysin situ TEMlithium-ion battery cathodeskinetic shortcutsamorphous intermediatesDRX oxides
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The pith

During sol-gel synthesis of disordered rocksalt Li1.2Mn0.4Ti0.4O2, local regions can skip thermodynamically stable intermediates by dissolving nanocrystals into an amorphous matrix that directly forms the target structure.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper tracks the early stages of crystallization in sol-gel prepared DRX cathode materials using nanoscale imaging. It shows that transformation paths are not uniform: some areas go through expected stable phases like spinel, while others use a faster route where intermediate crystals redissolve and the DRX phase nucleates straight from a local amorphous pool. These differences arise from uneven mixing in the gel, where transition metals bind differently than lithium. Bulk measurements miss this local variation but confirm the overall path goes via intermediates. The work suggests that controlling the precursor chemistry could steer the process toward more consistent results.

Core claim

In situ heating TEM reveals two distinct local pathways during thermal activation of the sol-gel precursor for DRX-LMTO: a classical multi-step transition through thermodynamically stable intermediates in some regions, and a kinetic shortcut in others where intermediate nanocrystals dissolve into a localized amorphous matrix that directly precipitates the DRX structure. Macroscale in situ SXRD shows the dominant path proceeds through spinel LMTO and lithium titanite intermediates, while FTIR links the diversity to chemically distinct microenvironments in the gel with stronger incorporation of transition metal ions into the acetate network.

What carries the argument

In situ heating transmission electron microscopy (TEM) using a liquid cell to visualize and identify the nanoscale crystallization pathways and their relation to precursor microenvironments.

If this is right

  • Local kinetic shortcuts can lead to more homogeneous DRX formation if the amorphous matrix route is favored.
  • Macroscopic characterization alone underestimates the diversity of transformation paths.
  • Tuning the sol-gel precursor composition could manipulate which pathway dominates to improve material quality.
  • The findings apply to other DRX oxides and sol-gel processes for battery cathodes.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Similar local variations might occur in other wet-chemical syntheses of complex oxides, affecting reproducibility.
  • Designing precursors to create uniform microenvironments could eliminate the need for high-temperature annealing in some cases.
  • This kinetic shortcut might enable lower processing temperatures or faster synthesis times for DRX materials.

Load-bearing premise

That the observed differences in local transformation pathways are mainly due to chemically distinct microenvironments in the gel precursor, with transition metals more strongly bound in the acetate network than lithium.

What would settle it

Direct observation of uniform transformation pathways across all regions in the precursor, independent of local composition variations, or absence of the amorphous matrix dissolution step leading to direct DRX precipitation.

read the original abstract

Sol-gel synthesis is a wet-chemical processing route for the fabrication of functional materials offering control over composition, morphology, and microstructure at relatively low processing temperatures compared to conventional solid-state synthesis methods. While the sol-gel process initiates with intermixed molecular precursors, the transformation pathways at the early nucleation stage are insufficiently understood. Here, the chemical and structural transformation of disordered rocksalt (DRX) Li1.2Mn0.4Ti0.4O2 (LMTO), a promising cathode material for lithium batteries, is studied by multiscale characterization tools. In situ heating transmission electron microscopy (TEM) using a liquid cell visualizes and identifies crystallization pathways at nanoscale. While some regions follow a classical multi-step transition through thermodynamically stable intermediates, others exhibit a kinetic shortcut in which intermediate nanocrystals dissolve into a localized amorphous matrix that directly precipitates the DRX structure. Macroscale FTIR corroborates the findings to be related to chemically distinct microenvironments in the gel precursor, with transition metal ions more strongly incorporated into the acetate-coordinated network than lithium. Although in situ heating TEM captures diverse local transformation pathways, in situ SXRD indicates that the macroscopic transformation proceeds predominantly through spinel LMTO and lithium titanite intermediates toward DRX-LMTO. The findings shed light on the spatiotemporal chemical and structural transformations in sol-gel derived DRX-LMTO materials, and call for fine tuning of such sol-gel chemistries to manipulate the crystallization pathways and achieve target material homogeneity more efficiently.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

3 major / 2 minor

Summary. The manuscript reports a multiscale experimental study of the sol-gel synthesis of disordered rocksalt Li1.2Mn0.4Ti0.4O2 (LMTO). In situ liquid-cell heating TEM is used to visualize nanoscale crystallization, revealing that some regions follow a classical multi-step pathway through stable intermediates while others exhibit a kinetic shortcut in which intermediate nanocrystals dissolve into a localized amorphous matrix that directly precipitates the DRX phase. Macroscale FTIR is interpreted as evidence that these diverse pathways arise from chemically distinct microenvironments in the gel precursor (transition metals more strongly bound in the acetate network than lithium). Complementary in situ SXRD indicates that the macroscopic transformation proceeds predominantly via spinel LMTO and lithium titanite intermediates to DRX-LMTO.

Significance. If the reported local kinetic shortcut is intrinsic to the sol-gel chemistry rather than an artifact, the work would provide direct visualization of non-classical nucleation pathways in DRX oxide synthesis and highlight opportunities to tune precursor microenvironments for improved homogeneity. The combination of liquid-cell TEM with FTIR and SXRD is a strength, but the absence of quantitative error analysis, direct nanoscale chemical mapping, and dry-heating controls limits the strength of the central claim.

major comments (3)
  1. [In situ heating TEM results (implied from abstract and methods)] The central claim that the dissolution-precipitation shortcut is an intrinsic feature of the sol-gel precursor microenvironments rests on liquid-cell in situ TEM observations. However, the liquid-cell geometry maintains a confined solvent environment during heating, which alters local ion diffusion, evaporation, and supersaturation relative to bulk gel drying. No control experiments with dry-heated or ex-situ samples are described to test whether the shortcut pathway persists outside the liquid cell.
  2. [FTIR and TEM correlation (implied from abstract)] The attribution of diverse pathways to chemically distinct microenvironments relies on macroscale FTIR, yet the manuscript provides no direct nanoscale chemical mapping (e.g., STEM-EDS or EELS) of the same regions undergoing the shortcut pathway before and during transformation. This leaves the causal link between precursor chemistry and observed kinetics unverified at the relevant length scale.
  3. [SXRD results (implied from abstract)] In situ SXRD shows the macroscopic transformation proceeds predominantly through spinel and lithium titanite intermediates, which appears to contradict the prevalence of the direct-precipitation shortcut observed locally in TEM. The manuscript does not quantify the fraction of material following each pathway or reconcile the local vs. bulk observations with error bars or statistical sampling.
minor comments (2)
  1. [Abstract] The abstract states that 'in situ heating TEM captures diverse local transformation pathways' but does not specify the number of independent regions or heating rates examined, which would help assess reproducibility.
  2. [Throughout] Notation for the target phase is inconsistent between 'DRX-LMTO' and 'DRX structure'; a single abbreviation should be defined at first use.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for the detailed and constructive report. The comments identify important limitations in the current presentation of our multiscale data. We address each major point below, indicating where revisions will be made to clarify the scope and limitations of the liquid-cell TEM, the correlative nature of the FTIR-TEM link, and the local-versus-bulk reconciliation.

read point-by-point responses

  1. Referee: The central claim that the dissolution-precipitation shortcut is an intrinsic feature of the sol-gel precursor microenvironments rests on liquid-cell in situ TEM observations. However, the liquid-cell geometry maintains a confined solvent environment during heating, which alters local ion diffusion, evaporation, and supersaturation relative to bulk gel drying. No control experiments with dry-heated or ex-situ samples are described to test whether the shortcut pathway persists outside the liquid cell.

    Authors: We agree that the liquid-cell geometry introduces differences in transport and supersaturation relative to bulk drying. The liquid cell was chosen specifically to capture the dynamics of the wet sol-gel precursor under heating. In the revised manuscript we will add a paragraph in the Discussion explicitly acknowledging this limitation, noting the absence of dry-heating controls, and discussing how the observed shortcut may be influenced by the confined environment. This will allow readers to assess the generality of the pathway. revision: yes

  2. Referee: The attribution of diverse pathways to chemically distinct microenvironments relies on macroscale FTIR, yet the manuscript provides no direct nanoscale chemical mapping (e.g., STEM-EDS or EELS) of the same regions undergoing the shortcut pathway before and during transformation. This leaves the causal link between precursor chemistry and observed kinetics unverified at the relevant length scale.

    Authors: We concur that direct nanoscale chemical mapping of the same regions would strengthen the causal connection. The present work correlates macroscale FTIR evidence of differential acetate coordination with the local TEM observations. In revision we will revise the relevant sections to describe the link as correlative rather than direct, emphasize this as a limitation, and note that future nanoscale mapping (STEM-EDS/EELS) would be required to confirm the chemical heterogeneity at the length scale of the observed pathways. revision: partial

  3. Referee: In situ SXRD shows the macroscopic transformation proceeds predominantly through spinel and lithium titanite intermediates, which appears to contradict the prevalence of the direct-precipitation shortcut observed locally in TEM. The manuscript does not quantify the fraction of material following each pathway or reconcile the local vs. bulk observations with error bars or statistical sampling.

    Authors: The manuscript already states that SXRD reflects the predominant macroscopic route while TEM captures local diversity. To address the concern we will expand the discussion to reconcile the scales: SXRD provides ensemble-averaged phase fractions, whereas TEM samples specific nanoscale volumes. We will add quantitative Rietveld-derived phase fractions from the SXRD data together with estimated uncertainties and discuss how spatially varying gel microenvironments can produce heterogeneous local pathways whose average matches the bulk SXRD evolution. revision: yes

Circularity Check

0 steps flagged

No circularity: purely observational experimental study with no derivations or self-referential claims

full rationale

The paper reports direct multiscale experimental observations (in situ liquid-cell TEM, macroscale FTIR, in situ SXRD) of crystallization pathways in sol-gel DRX synthesis. No equations, fitted parameters, ansatzes, uniqueness theorems, or mathematical derivations appear in the provided text or abstract. Claims about classical vs. kinetic-shortcut pathways rest on imaging and spectroscopy data, not on any reduction to prior inputs by construction. Self-citations (if present) are not load-bearing for the central observational results. This is self-contained empirical work; the skeptic concerns address experimental representativeness, not circularity.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The paper is entirely experimental and relies on established characterization techniques without introducing new free parameters, ad-hoc axioms, or postulated entities.

axioms (1)
  • standard math Established principles of transmission electron microscopy, Fourier-transform infrared spectroscopy, and synchrotron X-ray diffraction accurately reflect the chemical and structural states during heating.
    Invoked implicitly when interpreting in situ observations and macroscale data.

pith-pipeline@v0.9.0 · 5622 in / 1288 out tokens · 47179 ms · 2026-05-08T02:45:38.290561+00:00 · methodology

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