Synthesis, Microstructure, and Electrical Conductivity of Eutectic Composites in MF2–RF3 (M = Ca, Sr, Ba; R = La–Nd) Systems
, Natalia A. Arkharova, Anna G. Ivanova, Nikolay I. Sorokin and Denis N. Karimov *Round 1
Reviewer 1 Report
This article demonstrates a comprehensive research study on fluorite eutectic composites, and the results are clearly and effectively presented. I would recommend this article for publication, provided that the following comments are properly addressed.
· Why do the authors emphasize the optimal ionic conductivity at 500 K in both the abstract and the main text? If the goal is to apply these composites in electrochemical devices, will these devices be operating at 500 K? What is the typical temperature range for electrochemical devices?
· In line 93, the abbreviations ‘(F and T)’ appear without prior definition in the main text, which could cause confusion among the broader audience. This issue should be addressed to enhance clarity.
· In Table 2, the 'calculated phase compositions' column is mentioned without any explanation provided in the main text. Could you clarify how these calculated phase compositions were obtained and what specific purpose they serve in the context of the study?
· In Table 2, I noticed that the sum of the F and T phase does not appear to be close to 1. Could you please explain the reason for this discrepancy and provide the composition of the remaining phase?
· In Figure 6, are the conductivity curves from other references accurately represented? For instance, when the x-axis value is 1.6, the y-axis value of curve 5 in reference [54] reaches about 3, whereas in Figure 6, it appears to be only around 1.
· Figure 6 lacks error bars for the data points. Is it due to the fact that the error bars are smaller than the data point symbols?
· Figure 6 shows the single crystal La0.95Ba0.05F2.95 exhibits superior conductivity compared to the eutectic composites. I am curious about the conductivity of such single crystal at 500 K in comparison to that of the eutectic composites. According to the authors, the eutectic composites possess improved mechanophysical properties and are easier to synthesize. Could you provide further elaboration on the trade-off between the decreased conductivity of eutectic composites and the advantages they offer. Specifically, how does this trade-off impact the selection and performance of these composites in various practical applications?
· In line 255, the title of section 3.4 appears to be repetitive, as it shares the same title as section 3.3. It would be more appropriate to revise it to something like 'Anisotropy of the ionic conductivity of composites'.
Some comments on minor points (typos, figure suggestions etc.):
· In line 43, ‘synthetized’ should be ‘synthesized’.
· In line 55, ‘some other [30] system’ could be ‘some other system [30]’.
· In line 103, ‘according’ should be ‘according to’.
· Figure 2 a should be adjusted to improve the clarity of the scale of the ruler and make it more visible.
· When using 'respectively,' it is common to add a comma before it. For example, in lines 98, 105, and 107, a comma is missing before 'respectively'.
· In the ‘Calculated phase compositions’ column of Table 2, both ‘F’ and ‘T’ should be Italicized to conform to proper formatting.
· Can you rephrase the sentence in line 274. I found it challenging to comprehend its meaning, and a clearer wording would be greatly appreciated
· In line 284, there is an extra left parenthesis ‘(‘.
Overall, this article is fluently written, but there are a few sentences could be improved for clarity.
Author Response
Thank you very much for such a careful consideration of our work and extensive comments. Certainly, the fulfillment of the referee's requirements significantly improved the content of our article from a scientific point of view.
Comment 1
Why do the authors emphasize the optimal ionic conductivity at 500 K in both the abstract and the main text? If the goal is to apply these composites in electrochemical devices, will these devices be operating at 500 K? What is the typical temperature range for electrochemical devices?
Response 1
The typical operating range of electrochemical devices is from room temperature (RT) to ~200 °C. [see S.V. Gopinadh et. all. Fluoride-ion battaries: State-of-the-art and future perspectives. Sustainable Materials and Technologies. https://doi.org/1016/j.susmat.2022.e00436; M.A. Nowroozi et. all. Fluoride ion batteries - Past, present, and future. J. Mater. Chem. A. https://doi.org/1039/DOTA11656D; Sobolev, B.P.; Sorokin, N.I.; Bolotina, N.B. Nonstoichiometric single crystals M1–xRxF2+x and R1–yMyF3–y (M – Ca, Sr, Ba; R – rare earth elements) as fluorine–conducting solid electrolytes. In: Progress in Fluorine Science, Tressaud, A., Poeppelmeier, K., Eds.; Publisher: Elsevier, Amsterdam, 2016, Volume 1, Chapt. 21, p. 465–491. https://doi.org/10.1016/B978–0–12–801639–8.00021–0].
The choice of a temperature of 500 K for comparison of samples is due to the following reasons. It is convenient to determine the conductivity values of materials at a temperature T = 500 K from the graphs of conductivity (σ) - inverse temperature (1000/T), in this case 1000/T = 2. The temperature value of 500 K falls within the upper limit of the operating range and characterizes medium-temperature electrochemical devices.
Comment 2
In line 93, the abbreviations ‘(F and T)’ appear without prior definition in the main text, which could cause confusion among the broader audience. This issue should be addressed to enhance clarity.
Response 2
Thank you very much for these comments. Of course, this is our omission. Explanation of the used abbreviations is done in section 2.1
Comment 3
In Table 2, the 'calculated phase compositions' column is mentioned without any explanation provided in the main text. Could you clarify how these calculated phase compositions were obtained and what specific purpose they serve in the context of the study?
Response 3
This is our omission. Appropriate explanations have been added to the text. These compositions were obtained from the actual cell parameters of eutectic alloys using the analytical concentration dependences of the lattice parameters of the M1– xRxF2 + x and R1 – yMyF3 – y phases according to Ref. [44−46].
The difference in the lattice parameters of these phases (see Tables 1 and 2) indicates a significant non-equilibrium of the eutectic alloys obtained by directional crystallization of melts. The lattice parameters are significantly less than the equilibrium values given in Table 1, and the regions of phase homogeneity also turn out to be smaller.
With rapid cooling of the crystallized composite, diffusion processes are inhibited, therefore, a nonequilibrium position of the solidus (in English literature, the same process is sometimes described in terms of "incipient melting") is realized. This disequilibrium is associated with the narrowing of the regions of solid solutions F- and T- based on both components [see Jackson, K. A. Lamellar and Rod Eutectic Crowth / K. A. Jackson, J. D. Hunt // Trans. Met. sos. AIME. 1966 Vol. 236, No. 8. R. 1129-1142. DOI: 10.1016/B978-0-08-092523-3.50040-X]
Comment 4
In Table 2, I noticed that the sum of the F and T phase does not appear to be close to 1. Could you please explain the reason for this discrepancy and provide the composition of the remaining phase?
Response 4
We thank the reviewer for this remark. A technical error has occurred. Of course, the sum of these values must equal one. We rechecked the data and made the appropriate changes to Table 2.
Comment 5
In Figure 6, are the conductivity curves from other references accurately represented? For instance, when the x-axis value is 1.6, the y-axis value of curve 5 in reference [54] reaches about 3, whereas in Figure 6, it appears to be only around 1.
Response 5
This remark at first scared us a lot. However, no error is observed.
In ref [54] data are given in the form of natural logarithm of the value (previously used in a number of works). In present work, all data are expressed as a common decimal logarithm.
Comment 6
Figure 6 lacks error bars for the data points. Is it due to the fact that the error bars are smaller than the data point symbols?
Response 6
The relative measurement error sdc did not exceed 5%, Ñ„s described in the experimental procedure. When using a logarithmic scale, this error becomes very small and the error bars are smaller than the data point symbols, and is usually not shown in graphs in articles.
Comment 7
Figure 6 shows the single crystal La0.95Ba0.05F2.95 exhibits superior conductivity compared to the eutectic composites. I am curious about the conductivity of such single crystal at 500 K in comparison to that of the eutectic composites. According to the authors, the eutectic composites possess improved mechanophysical properties and are easier to synthesize. Could you provide further elaboration on the trade-off between the decreased conductivity of eutectic composites and the advantages they offer. Specifically, how does this trade-off impact the selection and performance of these composites in various practical applications?
Response 7
The conductivity of the 68LaF3×32BaF2 eutectic composite is 7.5 times lower than that of the La0.95Ba0.05F2.95 single crystal (at 500 K). However, the synthesis of eutectic composites, as compared with the growth of fluoride single crystals from a melt, is less costly in technological and financial terms. In addition, eutectics have good mechanophysical characteristics due to the absence of cleavage inherent in crystals and deceleration of dislocations at grain boundaries and interphase ones. Detailed data on La1-yBayF3-y solid solution crystals grown from the melt can be found in the article [Buchinskaya I.I., Karimov D.N., Sorokin N.I. La1-yBayF3-y solid solution crystals as an effective solid electrolyte: growth and properties. // Crystals. 2021. V. 11. No. 6. P. 629. https://doi.org/10.3390/cryst11060629]. There is also an overview of some of the properties of these crystals.
Comment 8
In line 255, the title of section 3.4 appears to be repetitive, as it shares the same title as section 3.3. It would be more appropriate to revise it to something like 'Anisotropy of the ionic conductivity of composites'.
Response 8
We are very grateful for this comment. A technical error occurred while loading text into the template. Section 3.4 does have a title 'Anisotropy of the ionic conductivity of composites'
Comment 9
Some comments on minor points (typos, figure suggestions etc.):
- In line 43, ‘synthetized’ should be ‘synthesized’.
- In line 55, ‘some other [30] system’ could be ‘some other system [30]’.
- In line 103, ‘according’ should be ‘according to’.
- Figure 2 a should be adjusted to improve the clarity of the scale of the ruler and make it more visible.
- When using 'respectively,' it is common to add a comma before it. For example, in lines 98, 105, and 107, a comma is missing before 'respectively'.
- In the ‘Calculated phase compositions’ column of Table 2, both ‘F’ and ‘T’ should be Italicized to conform to proper formatting.
- Can you rephrase the sentence in line 274. I found it challenging to comprehend its meaning, and a clearer wording would be greatly appreciated
- In line 284, there is an extra left parenthesis ‘(‘.
Response 9
We are grateful for the finding a typos and suggestions for improvement. These remarks have been corrected in the text. We also tried to improve the quality of the English language.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
In this manuscript, the study is well-structured, providing a comprehensive investigation of phase composition, morphology and temperature dependences of fluorine ionic conductivity of fabricated composites. I would like to recommend its publication before the below question is addressed.
1. The ruler of Figure 2a is not clear.
2. The caption of right inset (La0.95Ca0.05F2.95) in Graphical abstract is too small to see.
Author Response
Reviewer #2
We would like to express our gratitude to the reviewer for checking the manuscript and making minor comments that will help make it clearer for readers and more visually perfect for perception.
Comment 1
The ruler of Figure 2a is not clear.
Response 1
The contrast of the ruler has been enhanced for a better visual experience. Additionally, the overall dimensions of the grown ingots are indicated in the text.
Comment 2
The caption of right inset (La0.95Ca0.05F2.95) in Graphical abstract is too small to see.
Response 2
Signatures of crystals in a Graphical abstract are written in an enlarged font. Graphical abstract is slightly transformed.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors have addressed all of my comments and I recommend this article for publication.
Reviewer 2 Report
Accept in present form
