First Observation of Quantum Diffusion in Non-Cubic Metal: Deuterium Diffusion in In

Round 1

Reviewer 1 Report

This is an interesting work on quantum diffusion. The results are very convincing as well. Authors have studied the diffusion of Deuterium in Indium, a BCT crystal, via quantum tunneling. With experimentally obtained data they came to the conclusion that it's not the crystal structure rather temperature, atomic packing factor and distance between the nearest equilibrium position of Hydrogen atom in the crystal that plays the crucial role in the quantum diffusion. At higher temperature it's the classical thermal diffusion and at low temperature quantum diffusion by tunneling is dominant. Authors have also studied the effect of vacancy concentration on the quantum diffusion and found that presence of vacancy enhances the quantum diffusion.

This is an interesting work that might provide valuable insights on the effect of Hydrogen in metals e.g, Hydrogen embrittlement. The research topic is suitable for this journal as well.

Following are the comments/suggestion that need to be addressed before it can be accepted for publication.

1. In the 'Introduction', the "NRAOL" is mentioned as the method used to determine the diffusion coefficient. There should be a reference/citation of that method.

2. In section-2 it is written "a sample is placed into a vacuum chamber of ...". The detail specification of the sample, e.g, dimension, purity etc. , is missing.

3. In section-1 (Introduction) it is written "Each method is characterized by a lower limit of meaningful D_{II}.....". The notation 'D_{II}' is not defined before.

4. In figure-2 the error bar is shown only for one data point in each curve. Is the error same for other data points in that curve? If so, it should be mentioned in the description. Same for figure-4.

5. In line-222 "which gas(?) the form".

 

 

 

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The article presents experimental data on the quantum diffusion of hydrogen in a metal with a crystal lattice other than bcc. These experiments were held for the first time.

Major points in the review article which need clarification, refinement, reanalysis, rewrites, and/or additional information and suggestions for what could be done to improve the article.

1.     Introduction. The most cited references in the article should be within the last 5 years. 75 % of cited links in the article were published before 2018. Whether there were unsuccessful attempts by researchers of studying deuterium quantum diffusion in metals?

2.     Line 74. What criteria do you use to evaluate the reliability of experimental data on hydrogen diffusion in scientific literature?

3.     Methods. Who developed the techniques of nuclear reaction analysis online (NRAOL)? Did you use industrial or self-laboratory equipment?

Minor points like figures/tables not being mentioned in the text, a missing reference, typos, and other inconsistencies.

1.     Figure 1. Please add the units to the plot.

2.     Line 158. What is NRA method?

3.     Please check the errors in the words (line 176, 222 etc).

General conclusion. The article can be accepted after major revisions.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

A very interesting topic, well presented.  I have two minor comments.

In the abstract/introduction you mention that the crystal structure is something other than BCC - rather than have the reader speculate perhaps a good idea to simply state BCT.

The observations of "bends" in diffusion plots is often associated with phase changes.  The bends are clearly demonstrated and the explanation may be clear to the authors but a reader may wonder about phase transformations. A statement from the authors to say there are no phase changes that can be associated with the change in slope of the diffusion plots (for example BCT-BCC or other such change) should be included.  In ferritic steels the martensitic (quenched-in} BCT structure is metastable and BCC is the stable structure that is obtained on heating that allows C migration.  I am not saying this type of phase change is happening but it is worth commenting that phase changes have been considered and dismissed.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

This article presents new experimental data on the quantum diffusion of hydrogen isotopes in a metal with a crystal lattice other than bcc. There have been no experimental works before. The work has originality and significance in the content.

The authors have made all the necessary corrections.

English language and style are fine, but a minor spell check is required in the text.

General conclusion. The article can be accepted in present form.

Author Response

Thanks for valuable remarks and questions.