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Yes—according to a 2025 study, low-density amorphous ice (LDA) is unlikely to be completely amorphous. Computer models containing tiny, randomly oriented crystalline ice grains separated by thick disordered regions reproduced measured structure-factor data better than a wholly amorphous model. A second experiment found that the way LDA is prepared affects the cubicity of ice formed when it later recrystallizes, a “memory” that is difficult to reconcile with total structural randomness.
The finding supports a mixed structural picture rather than a simple choice between “perfect crystal” and “glass.” It does not directly image nanocrystals, determine a universal crystal fraction or size, or settle every difference between LDA samples.
What low-density amorphous ice is
Low-density amorphous ice is a solid form of water whose molecules do not display the long-range repeating lattice of ordinary crystalline ice. It is called “low-density” because its average density is lower than that of liquid water and many crystalline ice phases. LDA is important in laboratory studies of water, in models of ice in space, and in arguments about how liquid water’s unusual properties might arise.
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Is LDA really amorphous?
The 2025 paper by Michael Benedict Davies, Alexander Rosu-Finsen, Christoph G. Salzmann and Angelos Michaelides argues that LDA is not fully amorphous. Their preferred interpretation is a heavily disordered material containing small crystalline grains with random orientations. Thick, structurally disordered regions separate those grains, so the sample is neither a single repeating crystal nor a collection of molecules arranged with complete randomness.
The authors reported that models with this partial crystallinity matched the experimental structure factor more closely than a wholly amorphous model. A structure factor is a pattern obtained from scattering measurements; it summarizes how structural features at different length scales contribute to the measured signal. Matching it does not produce a photograph of individual grains, but it provides a quantitative test of competing atomic models.
The primary account is the article “Low-density amorphous ice contains crystalline ice grains” in Physical Review B 112, 024203, published on 7 July 2025.
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How the evidence was assembled
1. Comparing structural models with measurements
The researchers used two widely used models of water to generate candidate LDA structures. They then calculated the structure factors expected from those structures and compared them with the experimental structure factor for LDA. Across those comparisons, the partially crystalline arrangements provided the better match.
This approach tests whether a proposed arrangement can reproduce the scattering signature already measured for LDA. It is indirect evidence: the study did not use a microscope or another technique to resolve and photograph nanocrystals inside an LDA sample. The conclusion is therefore about which structural model best explains the available data, not a direct image of every grain.
2. Testing for a preparation-route memory
A mixed structure makes a further prediction. If LDA contains nanocrystalline regions, the details of how it forms should influence those regions. When the material is warmed and recrystallizes, that hidden structural history could affect the mixture of ice polymorphs produced.
The study compared LDA made by different preparation routes and examined the cubicity of the ice that formed during subsequent recrystallization. The resulting cubicities differed with the starting route. The authors interpret this dependence as a memory effect: the starting LDA retained information about its preparation that influenced the later crystal-growth process.
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What the proposed nanocrystalline structure looks like
Imagine many tiny ice crystallites, each with its own orientation, distributed through a thicker disordered matrix. Inside a grain, water molecules follow a locally crystalline arrangement. At a boundary, two differently oriented grains meet. Molecules in those boundaries cannot satisfy both crystal patterns at once, so they can be pulled away from the arrangements found inside either grain.
Chemistry World’s report describes these boundary molecules as capable of adopting more complex disordered structures. Those boundary and matrix regions help explain why LDA can look amorphous in bulk measurements even if ordered nanometre-scale domains are present.
This model also explains why calling LDA simply “crystal” would be misleading. The grains are not a continuous lattice, and the disordered regions are not a minor surface imperfection. Both components contribute to the measured structure.
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Wholly amorphous and partially crystalline models compared
| Feature | Wholly amorphous model | Partially crystalline model supported by the 2025 study |
|---|---|---|
| Long-range arrangement | No crystalline domains are assumed. | Small crystalline grains are present, with random orientations. |
| Disordered material | Disorder extends throughout the structure. | Thick disordered regions and grain boundaries separate ordered grains. |
| Fit to the measured LDA structure factor | Less successful in the reported comparisons. | Better agreement for the two water models examined. |
| Expected preparation memory | No clear ordered template should preserve route information. | Nanocrystalline regions can retain route-dependent structural differences. |
| Direct visual confirmation | Not applicable. | Not provided by this study; the evidence is model comparison plus recrystallization behavior. |
What “memory” in recrystallization means
Cubicity is the proportion of cubic character in ice formed during recrystallization, as opposed to hexagonal character. The paper reports that LDA made through different routes produced different cubicities on recrystallization. The result does not establish one universal cubicity for all LDA, nor does the available evidence provide a single percentage that applies to every preparation.
The significance is comparative: changing the formation route changed the later crystallization outcome. That dependence indicates that the starting material carried structural information forward. In the authors’ interpretation, nanocrystallites or related local order provide a physical way to store that information.
LDA-I and LDA-II: a qualification to the interpretation
The paper discusses two forms or preparation histories referred to as LDA-I and LDA-II. Their models are highly similar. The reported differences can be attributed to subtle variations in crystallinity, experimental uncertainty, or both. This qualification matters because it prevents an over-simple claim that LDA-I and LDA-II are entirely different materials with sharply separated structures.
The result supports partial crystallinity as a useful explanation of the data, while leaving room for small structural distinctions and measurement error. It does not show that every LDA sample has an identical arrangement of grains, boundaries and disordered regions.
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Why the finding matters for water and ice science
Reinterpreting a widely used reference material
LDA is often treated as a reference form of non-crystalline ice. If it contains ordered nanoregions, calculations and experiments that assume complete amorphousness may need to account for local crystallinity. Properties attributed to “amorphous ice” could reflect a combination of grain interiors, grain boundaries and the disordered matrix.
Clues about liquid water
The authors say the result may bear on understanding liquid water. LDA is not liquid water, and the study does not demonstrate that nanocrystals in LDA explain water’s anomalies. The connection is that competing models of water’s structure often use amorphous and crystalline ice as reference states. A more accurate description of LDA can therefore sharpen, rather than settle, those broader discussions.
Ice in cosmic environments
LDA is relevant to cosmic ice, where water can condense or transform under conditions unlike those on Earth. Understanding whether such ice is completely disordered or contains local crystal order affects models of its transformations as temperature and pressure change.
Possible astrobiological implications—and their limits
Chemistry World connects the result with hypotheses in which biomolecules could travel to Earth inside icy grains. A completely crystalline interior generally offers less disordered volume than an amorphous matrix for trapping or accommodating complex molecules. The proposed structure still contains thick disordered regions, so it does not remove the possibility that icy grains could host biomolecules.
That is context, not a result tested by Davies and colleagues. The study did not load LDA with biomolecules, measure their survival or transport, or establish that cosmic ice has the same grain structure as a laboratory sample. Any astrobiological conclusion remains a hypothesis that would require separate experiments and observations.
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What the study establishes—and what it does not
- Established by the reported evidence: partially crystalline models gave a better structure-factor match than wholly amorphous models in the comparisons performed.
- Established by the recrystallization test: LDA made by different routes produced different cubicities when recrystallized, showing a preparation-route dependence.
- Supported interpretation: LDA can contain small crystalline grains embedded in disordered regions.
- Not established: direct images of individual nanocrystals inside LDA.
- Not established: a universal nanocrystal size, crystal fraction or cubicity for all LDA samples.
- Still uncertain: how much of the LDA-I/LDA-II distinction reflects crystallinity rather than experimental error.
- Outside the study’s scope: whether biomolecules are transported in cosmic LDA or whether this structure alone explains liquid-water anomalies.
Questions the next experiments need to answer
The model comparison identifies a structural explanation, but several measurements would make that explanation more specific. Researchers need methods that can distinguish grain interiors from boundaries, estimate the distribution of grain sizes and determine how the disordered regions vary with preparation route. Repeating the structure-factor analysis with additional water models and independent experimental datasets would test how robust the preference for partial crystallinity is.
It is also important to separate intrinsic differences between LDA-I and LDA-II from experimental uncertainty. If route-dependent cubicity can be predicted quantitatively from a measured starting structure, the memory interpretation would become stronger. Conversely, if nominally identical preparations produce broad and irreproducible outcomes, that would place limits on how uniquely the nanocrystalline model can be inferred.
How scientists describe the result
Christoph Salzmann, the study’s corresponding author at University College London, told Chemistry World: “We now fully appreciate the complexity of the material, but this leads us on to the next steps of investigation.” The statement reflects the paper’s balance: the data favor a more complex structure, while the detailed arrangement remains an active subject of study.
Alexander Shluger, a UCL researcher who was not involved in the work, said the finding “will strongly contribute to the ongoing discussion of atomic structure of non-crystalline solids with a unique and insightful perspective on the structure of low-density amorphous ice”. His comment places the result in a wider debate about how solids can combine local order with bulk disorder.
Bottom line for readers
The strongest current answer to “Is low-density amorphous ice really amorphous?” is: not completely. The 2025 evidence favors LDA as a mixed material—randomly oriented crystalline grains surrounded by substantial disordered ice—because that model fits the measured structure factor and explains why preparation route changes later recrystallization cubicity. It is a structural inference, not a direct nanocrystal image, and it leaves the exact grain population, the LDA-I/LDA-II distinction and any biological consequences open for further work.
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