Peer review of: Dielectric ordering of water molecules arranged in a dipolar lattice (2020)

Reviewers' comments:
Reviewer #1 (Remarks to the Author):

Based  on  experimental  and  DFT-MD  simulations,  the  authors  conclude  that  the  water 
molecules  confined  in  the  Nano  channels  of  cordierite  crystal  are  experienced 
ferroelectric order-disorder phase transition at 3 K. I have some comments on this work, 
and the comments are listed below: 

1.  To let the readers have a clear picture of the structure of the material investigated 
in  this  work,  the  authors  should  present  the  molecular  structure  of  the  material 
they employed, especially details of the channels of the structure and how are the 
water molecules arranged inside the channels? 

2.  Since the ferroelectric phase transition is observed, can the authors detect the P-E 
hysteresis loops?   

3.  In the “Discussion” part, the authors wrote “Tc= -15 K”. How could the transition
temperature below 0 K? 

4.  The vdW interaction plays a main role between the confined water molecules and 
the  cordierite  crystal,  thus  dispersion  corrected  density  functional  should  be 
selected in the DFT computations, e.g. the non-local dispersion corrected vdW-
DF2 functional, one of the best functionals to account for the vdW interactions as 
suggested  by  previous  studies.  The  authors  should  at  least  report  a  test  DFT 
simulation by using the dispersion corrected functional? 

5.  As shown in Figure 3, for the “In channel” case, it seems a 180° rotation occurred 
from 100 K to 75 K. Did that really occur? Are the left picture and the right one 
reversely placed at 75 K? If it really occurred, the authors should provide a video 
to show that. 

6.  Also in Figure 3, I am not fully convinced that the water orientations shown at 10 
K depend on the final structure snapshots at 150 K due to the temperatures are too 
low to make obvious variation of the water orientations at 100 K, 75 K, and 10 K. 
Are the water orientations always the same at the final time at 150 K? If the water 
orientations change, would they always align as shown in the figures at 10 K of 
Figure 3? 

7.  For the DFT-MD simulations, the authors should include more water molecules. 
It is too limited to draw the conclusions only based on two water molecules for 
both  the  “In  channel”  and  “In  plane”  case?  At  least  four  water  molecules  are 
encapsulated at the same time for each case, and the more the better. In addition, 
please provide a video for each DFT-MD trajectory. 

8.  What is the reliable evidence for the water dipole orientation as shown in Figure 

4b?   


Reviewer #2 (Remarks to the Author): 

The manuscript titled “Dielectric ordering in dipolar lattice of water in cordierite” reports an order-
disorder type phase transition at 3K. The authors attempt to claim that there is ferroelectric H2O 
dipole moment by measurements of permittivity and specific heat. The direct evidence of ferroelectric 
water ice in geometrically confined systems are fundamentally important, which has been extensively 
studied in theory over past decades as already mentioned by authors. Nevertheless, serious concerns 
have to be raised in case a wrong conclusion may mislead the readers who are not professional in 
ferroelectricity, which prevents the publication of this manuscript: 
1, the temperature-dependent permittivity demonstrates a giant dielectric loss, which is not observed 
in the water-free sample. This temperature-dependent anomaly in dielectric constants corresponds to 
the huge dielectric loss. This is a clear indication that the transition is not ferroelectric transition. 
2, the authors claim that there is a relaxation behavior in the frequency-temperature spectra. But this 
is controversial to the data shown in figure 1 a. We can clearly see that dielectric behavior in 1 kHz 
measurement are totally different with the ones of 1 Hz, 1.64 kHz, 900 kHz. The 1 kHz data shows a 
level off of the dielectric constant even at very low temperature (<1 K), which is a hint of possible 
quantum paraelectricity (refer to the case of SrTiO3) or extrinsic artifacts. However, this is not shown 
in 1 Hz, 1.64 kHz, 900 kHz. 
3, based on the specific heat measurement, there is a so-called structural transition near 3 K. This is, 
again, far away from the observation of the dielectric anomaly (5-10 K). 

The only two experimental data in this manuscript are not self-consistent. Even so, an anomaly in 
specific heat or dielectric is just a minor hint of ferroelectricity. In order to make a reasonable 
argument, pyroelectric measurement and other probe-based techniques should be adopted. It is 
strongly suggested that the authors should double-check their experimental data and techniques. 
Although ferroelectricity in water ice is well studied in theory, a direct experimental evidence is 
important and should be super careful before the publication. 



Reviewer #3 (Remarks to the Author): 

The authors present an interesting study of the dipolar order of water in cordierite. In particular the 
authors perform dielectric measurements as a function of frequency and temperature in a hydrated 
cordierite sample. 
Their results indicate the existence of a order-disorder ferroelectric phase transition that occur at T=3 
K. 
This is quite an experimental achievement, given that the phase transition is due to the ordering of 
water molecules encapsulated 
The study is very interesting and certainly worth publishing in this journal. 
However, it needs important modifications in order to make the science and 
the relevant messages more clear to both the general and field specific audience. 

1.- The authors state at the beginning of the introduction that: 
"For decades intense research activities tackle the question whether water molecules with their rather 
strong dipole moment of p=1.85 Debye can condense into a ferroelectrically or antiferroelectrically 
ordered state. In liquid water or in H2O ice no such ordering occurs because a complex time-
dependent tetrahedral molecular hydrogen-bonded network emerges governed by Pauling's ice rules" 
However this is not correct. There is a well known order-disorder ferroelectric phase transtion in ice-ih 
to ice-XI. Details can be found in 
Betül Pamuk, Philip B. Allen, and M.-V. Fernández-Serra 
Phys. Rev. B 92, 134105 and references there in. 
This needs to changed because right now the manuscript makes incorrect statements. 

2.- The paper absolutely needs to have an atomistic picture of water in cordierite. I.e. For full 
understanding of the ordering it is not enough to provide the sketch in Fig 4b. Indeed this picture is 
very confusing, and while it can remain, it should be accompanied by an equivalent atomistic picture. 

3.- The ab initio results are surprising, but somehow need further explanation. 

Here are my questions: 

1.- without looking at the atomistic structure of the channel it is difficult to understand why the in plan 
order should be different from the out of plane order. The authors should provide some insight about 
why this happens. 
Are the 4 nanocages in the unit cell exactly identical? 
What is the distance between dipoles in plane versus out of plane? 

Why didn't the authors do a simulation with 4 water molecules? This would confirm for sure that the 
results are consistent with the picture they provide. 

2.- With respect to the last point, the authors could show the potential energy landscape of rotating 1 
molecule (or dipole) while leaving the other one fixed. This can be done for the 4 molecules in the unit 
cell, without the need to do ab initio MD simulations. The question this would address is if the coupling 
between the dipoles is electrostatic or if it needs also to be coupled to some vibrational degree of 
freedom of the cages. 

Only when the authors clarify my questions I will be willing to accept the manuscript for publication. 
Right now it needs substantial revision. 




Reviewer #4 (Remarks to the Author): 

The manuscript titled "Dielectric ordering in dipolar lattice of water in cordierite" realized in 
experiment the long-range dipolar ordering of water, which represents a big step towards achieving 
the (anti-)ferroelectric control of the confined water phases. This is enabled by confining the water 
molecules in specially designed nanosized cages, whose dimensions suppress the hydrogen-bonding 
interaction but still maintain the diploar interaction between the water molecules. The key evidence of 
the order-disorder type phase transition comes from the temperature-dependent measurements of the 
broad-band permittivity and specific heat, showing the transition temperature around 3 K, which is 
further supported by density functional theory calculations. Those results are very interesting and may 
trigger further studies on searching for various dipolar ordering of water in confined geometry, which 
may find practical applications in nanoelectronic devices. I recommend the publication of this work 
after the following issues are addressed. 

1. It would be better to add a schematic figure in Fig. 1 to show the crystalline cordierite 
(Mg,Fe)2Al4Si5O18, where the water molecules are confined in the nanosized channels with structural 
anisotropy. 

2. I am not the expert on the dielectric permittivity and specific heat measurement, but it seems that 
the experiments were delicately performed in a very broad frequency range, ν=1 Hz – 3 THz, and 
covering temperatures down to 0.3 K. Here I would like to comment on the DFT-MD simulation part. 
The authors only simulated two water molecules located next to each other along the channel c-axis, 
and two water molecules within the ab-plane. However, the real system is long-range ordered and 
contains much more water molecules. It is well known that three-body systems may behave very 
differently compared to two-body systems. It would be good to simulate three water molecules in the 
same way to test the robustness and generality of their conclusion. 

3. Page 5, 4th paragraph. It is stated that the ferroelectric orientation is characterized by a slightly 
lower potential energy (about 3 meV), than the antiferroelectric orientation. Such an energy difference 
might be too small to stabilize the ferroelectric orientation, even at very low temperature 3 K (the 
temperature for order-disorder type phase transition). If the energy of ferroelectric and 
antiferroelectric phases is so close, it would be very difficult to observe the order-disorder type phase 
transition at 3 K.