Investigation of AgI-Based Solid Solutions with Ag2CO3
Round 1
Reviewer 1 Report
The manuscript describes the investigation of AgI-Ag2CO3 phase diagram with regard to solid solution formation and its influence on the electrical conductivity.
The topic is interesting, however, some comments should be addressed prior to publication:
Sicne the manuscript is submitted to the topic of "Innovations in Materials processing", the introduction should state more clearly, how the conducted experiments and obtained results help with processing of the investigated materials.
Within the abstract and the manuscript, the authors highlight the fact, that the solid solution is formed by mixing at room temperature, however, no comment in made with regard to the effect of water used in the mixing process. What is the possibility of dissolving small amounts of AgI and Ag2CO3 within the water used for mixing and forming the solid solution upon evaporation?
Details regarding the parameters refined in Rietveld refinement should be given, considering the lattice parameters are used to determine the solubility limit.
There should be a comment, how the authors verified that Ag2CO3 did not decompose during the heating step to 148 °C, especially since the main reflections can be seen in the 10% sample in Fig 1.
In Figure 2, the absence of Ag2CO3 is noted, however, the amount of Ag2CO3 is 5% at maximum (if not decomposed during heating step). Is this amount significant? At which Ag2CO3 fraction do the authors expect powder XRD, and their instrument in particular, to be able to significantly detect Ag2CO3.
The authors state the occurance of Ag17(CO3)3I11 at > 7%, however, there is no XRD pattern of a heat treated sample showing this. The composition shown in Fig 2 should be expanded to include this significant composition.
The various methods applied to different sample compositions seems inconsistent. While the XRD measurements on the broad spectrum of compositions on pre-heated samples is fine, the XRD measurements on heat treated samples focuses on compositions up to 5%, whereas the other methods are applied to compositions up to 7% or 21%. Showing the XRD patterns of heat treated samples with composition 7-21% should show additional reflections from segregated phases/new phases, once the solution limit is exceeded.
Describing Figure S2 is confusing. Why is this singled out, but included in the supporting information. Starting the presentation of thermal measurements with this is confusing, especially when the 2nd endothermic peak has not been explained previously.
Please explain why the composition independent endothermic peak at 133 °C is attributed to pure AgI, when the phase transition takes place at 147 °C.
The “Discussion” is more a summary and outlook. The results of the previous sections are summarized, but not discussed (e.g. which method results in the most reliable determination of solution limit and why). This impression is reinforced by using past tense.
Author Response
We are grateful for the constructive comments from the reviewers.
Our response is shown in the attached document.
Author Response File: 
Author Response.docx
Reviewer 2 Report
This is an interesting paper on an old and still hot research theme. It will surely merit publication after authors will have considered the following complements.
1. Authors assume that the new peak in figure 5 corresponds to same beta/gamma to alpha transition as for neat AgI, except that a given amount of CO3 groups were incorporated and lowered the transition temperature. XRD in temperature above the transition would be a definitive proof, if this experiment was technically possible.
1a. Authors should complete their DTA measurements of figure 5 with DSC experiments, at least for composition x=1%, 3% and 5%. This would allow to confirm if the peak proportions are effectively the same on heating and on cooling. Additionally, DSC experiments will give access to the enthalpy changes of the transitions, which should be compared for 1% and 5% compositions giving single peaks.
1b. It is not clearly mentioned whether DTA samples in figure 5 were pretreated with uniaxial pressure to suppress the beta phase. Otherwise, authors should do additional DTA experiments on the pretreated samples to probe the same state as the XRD samples in figure 2.
1c. It would be surprising that the gamma phase and the beta phase had exactly the same transition temperature to the alpha phase. If authors confirm this point, they should make a specific comment.
2. Since the ICDD data gamma and beta phases of AgI are available, authors should use the peak proportions in XRD patterns of figure 4 to estimate the residual beta phase amount.
3. Just a detail: to avoid confusions, authors should relabel SI legends to S1 and S2, instead of 1 and 2.
Author Response
We are grateful for the constructive comments from the reviewers.
Our response is shown in the attached document.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
Thank you very much to the authors for their thorough answering of my previous comments.
I think the few, minor comments remain and could be improved.
The description of the Rietveld refinement process should include the parameters refined. The authors in their cover letter state that profiles, background and scale factors have been refined, however, do not mention this in the manuscript. It should be included (e.g. line 75 or 126)
For more clarity, the description of the 2nd endothermic peak in thermal data should be revised as follows: “ […]assumed to be the result of the ß/γ-to- α phase transition of AgI-based solid solution, […] (line 176f)
I still suggest to combine the “Discussion” and “Conclusion” parts into one section for “Conclusion” or “Summary”, since there is no discussion which method is most accurate or sensitive to determine the solubility limit or why CO3-richer or –poorer phases are not detected with XRD .
Author Response
We thank the reviewer for the comments. We have carefully revised our manuscript, in which the revised parts are marked up using the “Track Changes” function.
Our response is as document.
Author Response File: Author Response.docx
Reviewer 2 Report
Authors little modified their manuscript but answered point by point to my concerns. Here are the point by point responses to their responses.
- My point: authors assume that the new peak in figure 5 corresponds to same beta/gamma to alpha transition as for neat AgI, except that a given amount of CO3 groups were incorporated and lowered the transition temperature. XRD in temperature above the transition would be a definitive proof, if it were technically possible.
Response of authors: we know that in-situ XRD for heated samples and DSC analysis are powerful tools for revealing the phase transition phenomena. Unfortunately, however, these analytic techniques are not readily available for us… We would like to incorporate these techniques in future work to clarify the phase transition phenomena.
My response: OK, variable-temperature XRD is not a very common technique. This is acceptable, providing that authors specifically mention in the main text that in situ XRD measurements are planned to validate and further clarify the phase transition phenomena.
1a. My point: authors should complete their DTA measurements of figure 5 with DSC experiments, at least for composition x=1%, 3% and 5%. This would allow to confirm if the peak proportions are effectively the same on heating and on cooling. Additionally, DSC experiments will give access to the enthalpy changes of the transitions, which should be compared for 1% and 5% compositions giving single peaks.
Response of authors: we know that in-situ XRD for heated samples and DSC analysis are powerful tools…
My response: DSC is a very common technique in material science laboratories and it is surprising that it is not available to authors. In the absence of such control experiments, authors should present discussion of figure 5 as provisional interpretation and a not as definitive conclusion.
1b. My point: it is not clearly mentioned whether DTA samples in figure 5 were pretreated with uniaxial pressure to suppress the beta phase. Otherwise, authors should do additional DTA experiments on the pretreated samples to probe the same state as the XRD samples in figure 2.
Response of authors: the samples in Figure 5 were not pretreated by uniaxial pressing…
My response: OK, just specifically indicate the condition of absence of pretreatment in legend or text, to remove any ambiguity for future readers. Some part of authors' argumentation would deserve to be included in ESI.
1c. My point: it would seem strange that the gamma phase and the beta phase had exactly the same transition temperature to the alpha phase. If authors confirm this point, they should make a specific comment.
Response of authors The reason why we use the term “β/γ-to-α phase transition” in this paper is because the phase transition between β-AgI and γ-AgI is not clearly defined. It does not necessarily mean that γ-AgI remains at the elevated temperature and transforms directly to α-AgI. The phase transition between γ-AgI and β-AgI is beyond the scope of this paper and will not be discussed further.
My response: convincing argumentation, but a specific comment is still needed in main text.
- My point: since the ICDD data gamma and beta phases of AgI are available, authors should use the peak proportions in XRD patterns of figure 4 to estimate the residual beta phase amount.
Response of authors: It is difficult to quantitatively evaluate the fraction of β-AgI because the major peaks of γ-AgI and β-AgI originally overlap, and in addition, the fraction of β-AgI in Figure 2 is very small. Based on the scale factors for the two phases in the Rietveld refinement, the residual β-AgI was estimated to be about 4%. This rough estimate is not shown in the paper.
My response: OK. I recommend indicating this rough estimation or at least indicating that the beta phase fraction is of few percent based on XRD patterns. Otherwise, future readers would not understand why this data is missing.
Author Response
We thank the reviewer for the comments. We have carefully revised our manuscript, in which the revised parts are marked up using the “Track Changes” function.
Our response is as document.
Author Response File: Author Response.docx
Round 3
Reviewer 1 Report
Thank you very much for responding to my comments. I think the manuscript has been improved sufficiently for publication.
