Investigation of the Phase Composition, Structural, Mechanical, and Dielectric Properties of (1 − x)∙ZrO₂-x∙CeO₂ Ceramics Synthesized by the Solid-State Method

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Authors,

you manuscript deals with the change of structure and properties in the zirconia cerai system with gradual change of composition. Your efforts have produced a vast amount of experimental results, however the paper also has some significant weaknesses which are listed in the following paragraphs.

Introduction:

What I missed was the importance of ceria zirconia materials in the field of heterogeneous catalysis, this should be added together with literature. Concerning the thermodynamics of the system you missed the paper of Maschio on mechanical properties in the zirconia ceria system (Journal of the European Ceramic Society 9 (1992) 127-132) which provides mechanical properties for some characteristic compositions. In case of dielectric properties there is a very recent study by Steiner et al. J Am Ceram Soc. 2023;106:2875–2892. Which should be listed and which can be used for comparison with your results in the discussion section.

Experimental:

It was probably not a good idea to start from powders with 5 µm size and rely on the power of the Frtitsch mill alone. There are sub-µm monoclinic zirconia easily available (ceria mills down without problems). The microstructures and EDS investigations show clearly that the powder mixtures were not fine grained and homogeneous enough, there are evidently compositional gradients. The effect of inhomogeneity is most clearly seen in the compositions with low ceria content. 12Ce-TZP is a standard composition which after sintering is entirely tetragonal, you failed to produce tetragonal phase 15Ce-TZP even with 5h dwell at 1500°C. More intense milling and slower heating in the temperature range between 1150°C and 1400°C may help. Your microstructures were simply too coarse and inhomogeneous, the ceria had not enough time to diffuse into the zirconia or the grains got too large.

The second important point is mixed valence Ce3+/Ce4+. Formation of trivalent Ceria is a matter of thermodynamics and driven by entropy increase due to loss of gaseous oxygen. The problem can be avoided by annealing at ~1200°C in air or oxygen, this reverts the loss of oxygen and changes the composition more to tetravalent. From my own experience Iknow that especially at low ceria contents this can be crucial (in my first efforts many years ago the samples were jumping off the plate during cooling)

Results & Discussion

In general Results and discussion should be separated, first show your graphs and tables and stay with the facts, put the discussion in a separate chapter.

You have interpreted your results concerning phase composition in terms of “the thermodynamic data are not contradictory and need to be corrected”. This is not the case, thermodynamics refer to the composition at sintering temperature used. Whether you can retain the high temperature composition after cooling is a question of grain size, stabilizer content (ceria), homogeneity, Ce3+/Ce4+ stoichiometry which all affect the martensite start temperature. I have another paper for review on my table where the authors succeeded to make an entirely tetragonal 10Ce-TZP (ultrafine starting powder and final grain size).

Density…

Figure 1. Density was different depending on composition especially the low ceria compositions are deviating. Here you should condider that the theoretical density of m-ZrO2 is significant lower than the density of t-ZrO2 (drawing the straight line is only valid if you can preserve the t or c-phase.

Figure2. it seems you milling process has a different effect on zirconia and ceria, can you provide Scherrer analysis of powders after milling to see the crystallite sizes). Ceria is milled better than zirconi leaing to higher shrinkage for the high ceria compositions.

Table 1: maybe you should order the samples in the way you arranged the title of the paper (from low to high x values)

Why does the X=0.7 composition reperesent an outlier ?

XRD and RAMAN data are consistent.

Figure 5: Microstructures: the flake formation is a bit strange is this some kind of furnace debris or really a part of the microstructure. Actually zirconia ceria microstructures should look like 5b or e. Some compositions are evidently not properly reacted.

Figure 7: same problem the blurry images show that the phase formation is not really complete, there are gradients in the grains.

Table 2: Nice to have but this is only interesting if you were able to determine some oxygen deficiency or not. If you keep the table plot the expected values for the compositions together with the results and interpret possible deviations (how exact can you measure, please comment on that)

Figure 7 appears twice !!

Next Figure 7 (a) grain size is OK. (b) is nonsense ! Scherrer analysis data are only valid for crystallite sizes << 100 nm in POWDERS !! not in sintered ceramics.

Fig. 8: Dielectric properties very interesting, pleas comment on the effects of inhomogeneities on the results.

Fig. 10: How relevant are microhardness data obtained from non-polished surfaces, either do this properly or comment on the effects of surface roughness.

By the way phase transformation always leads to overestimation of hardness and Young’s modulus in microindentation measurements of transformation toughened compositions (tetragonal with not too much stabilizer). The volume expansion triggered by phase transformation counteracts indenter force.

Conclusions:

Deviations from phase compositions predicted by thermodynamics are to a large part due to experimental limitations, X= 0.15 should be totally tetragonal. The thermodynamic data are widely correct.

Author Response

Dear reviewer,

The authors of the manuscript with the title “The Investigation of the Phase Composition, Structural, Mechanical, and Dielectric Properties of (1-x)∙ZrO₂-x∙CeO₂ Ceramics Synthesized by the Solid-State Method” are very grateful for your rigorous analysis of this work. We especially appreciate how you generously shared your experience in the field of obtaining zirconia ceramics. We thoroughly analyzed your helpful comments and perceived weaknesses in our work. We tried to answer all your remarks below. All comments were divided for better understanding.

 

Comment 1. “Introduction:

 

What I missed was the importance of ceria zirconia materials in the field of heterogeneous catalysis, this should be added together with literature. Concerning the thermodynamics of the system you missed the paper of Maschio on mechanical properties in the zirconia ceria system (Journal of the European Ceramic Society 9 (1992) 127-132) which provides mechanical properties for some characteristic compositions. In case of dielectric properties there is a very recent study by Steiner et al. J Am Ceram Soc. 2023;106:2875–2892. Which should be listed and which can be used for comparison with your results in the discussion section.”

 

Response 1. Dear reviewer, done

Thank you for these comments. We included some references in the introduction section and added sentence describing the importance of ceria-zirconia materials in the field of heterogeneous catalysis. Also, we added references suggested by you in the text. All changes are outlined by a yellow color.

 

Comment 2. “Experimental:

 

It was probably not a good idea to start from powders with 5 µm size and rely on the power of the Frtitsch mill alone. There are sub-µm monoclinic zirconia easily available (ceria mills down without problems). The microstructures and EDS investigations show clearly that the powder mixtures were not fine grained and homogeneous enough, there are evidently compositional gradients. The effect of inhomogeneity is most clearly seen in the compositions with low ceria content. 12Ce-TZP is a standard composition which after sintering is entirely tetragonal, you failed to produce tetragonal phase 15Ce-TZP even with 5h dwell at 1500°C. More intense milling and slower heating in the temperature range between 1150°C and 1400°C may help. Your microstructures were simply too coarse and inhomogeneous, the ceria had not enough time to diffuse into the zirconia or the grains got too large.

 

The second important point is mixed valence Ce3+/Ce4+. Formation of trivalent Ceria is a matter of thermodynamics and driven by entropy increase due to loss of gaseous oxygen. The problem can be avoided by annealing at ~1200°C in air or oxygen, this reverts the loss of oxygen and changes the composition more to tetravalent. From my own experience Iknow that especially at low ceria contents this can be crucial (in my first efforts many years ago the samples were jumping off the plate during cooling)”.

 

Response 2. Dear reviewer, - done

Thank you for these comments. Especially for sharing your experience about your experiments.

We totally agree with the remarks that you made and understand the importance of particle size distribution and the homogeneity of the initial mixture. Unfortunately, we don’t have enough time to redo all experiments with ultrafine zirconia (nanosized) and ceria powders due to the long time of delivery from our suppliers. Also, it is impossible for us to sinter samples with different heating rates or milling times and conduct all sets of measurements (XRD, SEM, EDS, Vickers hardness) because it will take several months to do this. We believe that, from a technological point of view, the results obtained in this manuscript are of interest because factors like inhomogeneity and thermal treatment regimes can significantly affect the phase composition, dielectric, and mechanical properties of ZrO₂-CeO₂ ceramics.

 The specifications of initial powders (Sigma Aldrich) don’t include information about the size distribution of powder particles. There is only information that the size of the powders is less than 5 μm. To analyze the size distribution of the initial powders, we conducted quick size distribution measurements on the Analysette 22 unit of dispersed water ceria and zirconia powders. The results are provided in Fig. 1. From these distributions, it can be seen that 60% of ceria particles have a size less than 1 μm. For initial zirconia powder, 100% of the particles were less than 1 μm. The mean size of ZrO₂ particles was 0.3 μm, while for CeO₂ particles, the mean size was 0.8 μm.

a)

b)

Fig. 1 – Histograms of particle size distribution. a) – initial powder of CeO₂; b) – initial powder of ZrO₂

 

According to these results, the sintering of experimental ceramics was done using ultrafine submicron zirconia powder and micron-sized ceria powder. We suppose that such distribution is enough to obtain homogenous ceramics.

From our experience, the sintering of zirconia-ceria ceramics from micron-sized powders at temperatures in the range of 1200 °C doesn’t lead to significant shrinkage. As porous ceramics are not the main object of this study, we sinter them at a temperature of 1500 °C (the possible maximum temperature of our furnaces). We understand that the lowering of temperature can be compensated by a longer time of sintering, but it will take too long to obtain dense ceramics in this case.

Also, we demonstrate that with the absence of special processing on micron-sized powders of zirconia and ceria, fully or partially tetragonal-stabilized ceramics can be obtained.

We outlined all changes in the text with a yellow color.

 

Comment 3. “In general Results and discussion should be separated, first show your graphs and tables and stay with the facts, put the discussion in a separate chapter.”

Response 3. Dear reviewer,

Thank you for this comment. The “Results and discussion” section was divided into “Results” and “Discussion” sections according to your suggestion.

All changes are outlined by a yellow color.

 

Comment 4. “You have interpreted your results concerning phase composition in terms of “the thermodynamic data are not contradictory and need to be corrected”. This is not the case, thermodynamics refer to the composition at sintering temperature used. Whether you can retain the high temperature composition after cooling is a question of grain size, stabilizer content (ceria), homogeneity, Ce3+/Ce4+ stoichiometry which all affect the martensite start temperature. I have another paper for review on my table where the authors succeeded to make an entirely tetragonal 10Ce-TZP (ultrafine starting powder and final grain size).”

 

Response 4. Dear reviewer, - done

Thank you for these comments. We agree with you that grain size, stabilizer content (ceria), homogeneity, and Ce3+/Ce4+ stoichiometry are the key factors for obtaining stabilized tetragonal zirconia. Nevertheless, we think that phase diagrams that are used by many technologists and material science engineers give information about cooled-down to room-temperature phase compositions. We think it is very important to demonstrate that there are some deviations in phase composition from known phase diagrams.

We rewrite our statement about thermodynamic data in less affirmative form and outline all changed sentences with a yellow color.

 

Comment 5. “Density…

 

Figure 1. Density was different depending on composition especially the low ceria compositions are deviating. Here you should condider that the theoretical density of m-ZrO2 is significant lower than the density of t-ZrO2 (drawing the straight line is only valid if you can preserve the t or c-phase.”

 

Response 5. Dear reviewer, - done

Thank you for this comment. We added theoretical densities of zirconia polymorphs on the Fig. 1.

 

Comment 6. “Figure2. it seems you milling process has a different effect on zirconia and ceria, can you provide Scherrer analysis of powders after milling to see the crystallite sizes). Ceria is milled better than zirconi leaing to higher shrinkage for the high ceria compositions.”

 

Response 6. Dear reviewer, - done

Thank you for this comment. We measured XRD patterns of initial and milled powders of zirconia and ceria, and results are provided in Fig. 2.

Fig. 2 shows the diffraction patterns of ZrO₂ and CeO₂ particles before and after grinding. Using the Scherrer equation, coherent scattering regions (CSR) were calculated for each of the samples. Peaks (11–1) and (111) for ZrO₂ and (111) and (200) for CeO₂ were used for the calculation. Table 1 presents the calculated FWHM values and coherent scattering regions. From the presented data, it is clear that after grinding, FWHM increases and, as a result, CSR decreases.

 

Fig. 2 - XRD patterns of ZrO₂ and CeO₂ powders; a) - ZrO₂ b) - CeO₂ c) - ZrO₂ after milling and d) - CeO2 after milling

 

Powder	(hkl)		FWHM	d, nm
ZrO2	(11-1)	28.20	0.16721	49.01
	(111)	31.51	0.17813	46.36
CeO2	(111)	28.56	0.10806	75.90
	(200)	33.10	0.10002	41.59
ZrO2 after milling	(11-1)	28.19	0.41211	19.89
	(111)	31.49	0.41437	19.93
CeO2 after milling	(111)	28.56	0.22007	37.27
	(200)	33.10	0.20488	40.47

 

By analyzing the obtained results, it can be concluded that there is no preferential effect on ceria or zirconia powders in the chosen milling regimes.

 

Comment 7. “Table 1: maybe you should order the samples in the way you arranged the title of the paper (from low to high x values)

 

Why does the X=0.7 composition reperesent an outlier?

 

XRD and RAMAN data are consistent.”

 

Response 7. Dear reviewer, - done

Thank you for this comment. We reordered samples according to your suggestion. There are some mistakes in the text of the table. For this reason, a sample with an X = 0.7 composition represents an outlier. We rewrote the information in the table and highlighted all changes with yellow.

 

Comment 8. “Figure 5: Microstructures: the flake formation is a bit strange is this some kind of furnace debris or really a part of the microstructure. Actually zirconia ceria microstructures should look like 5b or e. Some compositions are evidently not properly reacted.”

 

Response 8. Dear reviewer, - done

Thank you for this comment. According to our results of size distribution and XRD (Fig. 2) data it can be seen that initial oxides were homogeneously mixed, so we can assume that solid-phase reaction is completed during the sintering process. Flake formation on the SEM images can be explained by the fact that, after making a chip on ceramics, some small particles cling to the surface by electrostatic force.

 

Comment 9. “Figure 7: same problem the blurry images show that the phase formation is not really complete, there are gradients in the grains.”

 

Response 9. Dear reviewer, - done

Thank you for this comment. The blurriness of the provided images can be connected with the resolution of the electron microscope.

 

Comment 10. “Table 2: Nice to have but this is only interesting if you were able to determine some oxygen deficiency or not. If you keep the table plot the expected values for the compositions together with the results and interpret possible deviations (how exact can you measure, please comment on that)”

 

Response 10. Dear reviewer, - done

Thank you for this comment. We tried to compare the expected composition with what was obtained from EDS data, and it didn’t fit so well, but the main trend remains unchanged. We provided some explanations about it in the text of the manuscript. With increasing x, the concentration of Ce atoms is also increasing. All changes have been outlined by a yellow color.

 

Comment 11. “Figure 7 appears twice !!

 

Next Figure 7 (a) grain size is OK. (b) is nonsense ! Scherrer analysis data are only valid for crystallite sizes << 100 nm in POWDERS !! not in sintered ceramics.”

 

Response 11. Dear reviewer, - done

Thank you for this comment. We remove the (b) figure and rewrite the numbers of the figures correctly in the text. All changes were outlined by a yellow color.

 

Comment 12. “Fig. 8: Dielectric properties very interesting, pleas comment on the effects of inhomogeneities on the results.”

 

Response 12. Dear reviewer, - done

Thank you for this comment. We include the influence of inhomogeneity on the dielectric properties of the obtained ceramics in the text of the manuscript. We outline all changes with a yellow color.

 

Comment 13.  “Fig. 10: How relevant are microhardness data obtained from non-polished surfaces, either do this properly or comment on the effects of surface roughness.

 

By the way phase transformation always leads to overestimation of hardness and Young’s modulus in microindentation measurements of transformation toughened compositions (tetragonal with not too much stabilizer). The volume expansion triggered by phase transformation counteracts indenter force.”

 

Response 13. Dear reviewer, - done

Thank you for this comment. We believe that tooling (grinding and polishing) can significantly affect the mechanical characteristics of ceramics. To avoid this, we conduct all measurements on unpolished surfaces. The roughness of samples increases the standard deviation, but even so, it can be seen that the main trends of microhardness changes in the obtained ceramics are still visible.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

1. Explain abbreviations used in the text, e.g., m → t transition  (line 139), c+t ceramics (line 158, 175), c+t or t phases  (line 183), D2 band (line 205), etc.
2. Correct the caption to Fig.2 for clarity. Please explain better.
3. It would be valuable to provide an example of fitting the calculated lattice constants and phase coexistence (given in the Tab.1).
4. It is not clear for the reader how the porosity was calculated (Fig.3a). What is apparent density (value and from what), etc.
5. Explain how phase content was calculated in the Fig. 3b
6. (line 210) at 244, 455 и (what is it?)
7. It is worth marking in Fig. 4 which vibration modes (mentioned in the text) are visible. The caption under Figure 4 and 5 has too little information.
8. SEM images are sei or bei?
9. What do you mean by "were proportional to the composition of the charge" (line 240)?
10. It would be valuable to label others peaks presented in the Figure 6.
11. What do you think about the compliance of the real composition with the nominal one (Presented in Table 2)?
12. Explain how did you distinguish the average grain size from the crystallite size (Fig.7)?
13. Correct the caption to Fig.9 and Fig.10. Explain better.
14. I suggest re-writing this article with better significance of content and novelty. Some results require better understanding and explanation by the authors.

 

Author Response

Dear reviewer,

Thank you for the time you spent on the detailed study of our manuscript. We find your comments extremely helpful. We hope that we were able to answer them and that the quality of the submitted manuscript increases after the review.

 

Here, below, we provide answers to your comments with our responses.

 

Comment 1. “Explain abbreviations used in the text, e.g., m → t transition  (line 139), c+t ceramics (line 158, 175), c+t or t phases  (line 183), D2 band (line 205), etc.”

Response 1. Dear reviewer,

Thank you for this comment. D2 band (D stands for defects)

The D1 band is associated with defect species like an oxygen vacancy, which disrupts the Oh symmetry, while the D2 band corresponds to MO₈-type defect species with Oh symmetry, including a dopant cation without any oxygen vacancy [A. Nakajima, A. Yoshihara, M. Ishigame, Defect-induced Raman spectra in doped CeO2, Phys. Rev. B: Condens. Matter Mater. Phys. 50 (1994) 13297−13307].

Another used abbreviation explained in the text of revised manuscript. All changes are highlighted in yellow.

 

 

Comment 2. “Correct the caption to Fig.2 for clarity. Please explain better.”

Response 2. Dear reviewer,

Thank you for this comment. The caption to Fig. 2 was corrected, and a better explanation was added to the text of the manuscript. All changes are highlighted in yellow.

 

Comment 3. “It would be valuable to provide an example of fitting the calculated lattice constants and phase coexistence (given in the Tab.1).”

Response 3. Dear reviewer,

Thank you for this comment. Actually, no fitting method was applied to the XRD patterns for the evaluation of lattice constants and phase composition. Bruker Soft Difrac Eva 2.1 allows us to refine the crystal lattice parameters manually with the use of the PDF 2016 database. Phase composition was also calculated by the corundum number method with the help of data included in PDF cards. The explanation of the methods used for processing diffraction patterns was added to the text of the manuscript. The added sentences were outlined by a yellow color.

 

Comment 4. “It is not clear for the reader how the porosity was calculated (Fig.3a). What is apparent density (value and from what), etc”

Response 4. Dear reviewer,

Thank you for this question. Apparent density is the density of a sample, which is calculated directly from the mass of the sample and its geometric parameters. In our work, we synthesized experimental samples in the form of tablets, so the apparent density was calculated with the following formula:

ρ_app = m/(π(d/2)²·h), where m – mass of a tablet; d – diameter of a tablet; h – thickness of a tablet.

The porosity can be estimated with the formula P = (1 - ρ_app/ρ_XRD)∙100%, where ρ_app is ap-parent density and ρ_XRD is X-ray density. XRD densities were calculated as a weighted mean value between all constituted phases according to the formula ρ_XRD = ρ₁·c₁+ ρ₂·c₂+… ρ_n·c_n.

 

Comment 5. “Explain how phase content was calculated in the Fig. 3b”

Response 5. Dear reviewer,

Thank you for this comment. Phase composition was obtained by corundum number method using DifracEva 2.1 and corundum numbers from the PDF cards. This explanation was introduced in the text of the manuscript and outlined by a yellow color.

 

Comment 6. “(line 210) at 244, 455 и (what is it?)”

Response 6. Dear reviewer,

Thank you for this comment. This was a typo which was corrected in new version of the manuscript.

 

Comment 7. “It is worth marking in Fig. 4 which vibration modes (mentioned in the text) are visible. The caption under Figure 4 and 5 has too little information.”

Response 7. Dear reviewer,

Thank you for this comment. We changed figures and captions according to your remarks. All changes were outlined by a yellow color.

 

Comment 8. “SEM images are sei or bei?”

Response 8. Dear reviewer,

All SEM images are backscattered electron images because Phenom ProX G6 electron microscope has only backscattered electron detector.

 

Comment 9. “What do you mean by "were proportional to the composition of the charge" (line 240)?”

Response 9. Dear reviewer,

Thank you for this question. The term “charge” was used for initial mixtures of oxides after the milling process.

 

Comment 10. “It would be valuable to label others peaks presented in the Figure 6.”

Response 10. Dear reviewer,

Thank you for this comment. All peaks on the EDX spectra were labeled according to your suggestion.

 

Comment 11. “What do you think about the compliance of the real composition with the nominal one (Presented in Table 2)?”

Response 11. Dear reviewer,

Thank you for this question. During the experiments, EDX data were compared to the expected composition according to the molar ratio between ZrO2 and CeO2. The real composition and the nominal one don’t compile, and we can give next explanations to this:

• Roughness of cross-section surfaces of ceramics obstructs precise detection of all elements;
• It is known that the concentration of oxygen acquired by the EDX method sometimes has a high error value.
• The analyzed square of the sample can be inhomogeneous.

 

Comment 12. “Explain how did you distinguish the average grain size from the crystallite size (Fig.7)?”

Response 12. Dear reviewer,

Thank you for this question. In our studies, we assumed that grain size always exceeded crystallite size. Nevertheless, due to the remarks of one of the reviewers, we decided to remove the dependence of crystallite size on concentration.

 

Comment 13. “Correct the caption to Fig.9 and Fig.10. Explain better.”

Response 13. Dear reviewer,

Thank you for this comment. The captions were corrected according to your remarks.

 

Comment 14. “I suggest re-writing this article with better significance of content and novelty. Some results require better understanding and explanation by the authors.”

Response 14. Dear reviewer,

Thank you for this comment. We tried to analyze the mistakes with an interpretation of the main results of this study and provided a better explanation according to your remarks. Also, in the introduction section, some new information was included to highlight the significance and novelty of the conducted research.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Overall the authors have done a great job of structrual-property characterization of ZrO2-CeO2 ceramics. The results are nice, structrual characterization covers almost every analytical methods (XRD, Raman, SEM etc). The correlance between crystal structure and dielectric behavior is carefully discussed. This paper is presented in a logical manner. I would recommend accepted after some comments are as followed:

1. If possible, a high temperature DSC can reveal crystal phase transformation details. It might be interesting to see if any curie point.

2. Fig. 5d might have electron charging. Were the samples coated with any gold?

3. For dielectric tests, silver paste is not accurate in terms of area calculation. Should coat with gold under a certain mask, then use silver paste to connect to the LCR meter.

4. For Fig 8b, line 2,3,4,5, these samples look too condutive. Maybe silverpaste went into the sample crack and somehow conducted. Please redo these samples.

5. A related paper would be recommended to cite, including details in nanomaterial structural characterization, dielectric studies,  instrumentation, and structural dielectric relationships: https://doi.org/10.1039/D3NR00350G

Author Response

Dear reviewer,

Thank you for your review and positive feedback on our manuscript. We carefully considered all your comments and gave our answers below.

 

Comment 1. “If possible, a high temperature DSC can reveal crystal phase transformation details. It might be interesting to see if any curie point.”

Response 1. Dear reviewer,

Thank you for this comment. You are right that the DSC method can give very useful information about phase transformations, but unfortunately, we don’t have this technique in our lab at this moment.

 

Comment 2. “Fig. 5d might have electron charging. Were the samples coated with any gold?”

Response 2. Dear reviewer,

Thank you for this comment.

All samples were coated with gold thin film (10 – 15 nm) before conducting SEM measurements.

 

Comment 3. “For dielectric tests, silver paste is not accurate in terms of area calculation. Should coat with gold under a certain mask, then use silver paste to connect to the LCR meter.”

Response 3. Dear reviewer,

Thank you for this comment.

We understand that the accuracy of the silver paste coating shape is much worse than the deposition of a thin gold film through the mask. To avoid this feature of inaccurate silver paste coating, the experimental samples were 0.9–1.1 mm thick. Such thickness makes it impossible to short circuit through a conductive channel, and silver paste film covers all squares of tablets. We assume that in this case, for the calculations of permittivity values, the use of geometric parameters for tablets is justified.

 

Comment 4. “For Fig 8b, line 2,3,4,5, these samples look too condutive. Maybe silverpaste went into the sample crack and somehow conducted. Please redo these samples.”

Response 4. Dear reviewer,

Thank you for this comment.

During the experiments, 3–4 tablets of each composition were sintered for different measurements. When we faced high conductivity and dielectric permittivity in some samples for the first time, we measured all 3 tablets for every concentration. All measurements showed high conductivity in the samples. Then samples with high conductivity were resynthesized from the beginning, and it came out that the electrical properties of the samples were reproduced. In this case, we assumed that the main reason for such electrical properties in the obtained samples was the intrinsic properties of the material.

We also presumed the penetration of silver paste into pores or cracks, but after analyzing cross-sections with an optical microscope and an electron microscope, no traces of silver paste were found.

 

Comment 5. “A related paper would be recommended to cite, including details in nanomaterial structural characterization, dielectric studies,  instrumentation, and structural dielectric relationships: https://doi.org/10.1039/D3NR00350G”.

Response 5. Dear reviewer,

Thank you for this recommendation. We included this article in our manuscript as you suggested.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Authors,

thank you for carefully revising the manuscript, from my point of view it can be accepted.

Author Response

Dear reviewer,

 

Thank you very much for your decision on the corrected version of our manuscript according to your review. We are very glad that you gave us a lot of useful and significant comments, which helped improve the quality of our work.

Reviewer 2 Report

Comments and Suggestions for Authors

1. It would be valuable to include some of the comments from the "Cover Letter" that the authors sent me in the manuscript. The text would be easier for the reader to understand.
2. It is enough to explain the abbreviations after his first use in the text.
3. What changes are in Table 1 apart from the reversed order compared to the previous version? 
4. Fig. 9b is very busy, and its caption is relatively poor.
5. I wrote:" Correct the caption to Fig.9 and Fig.10. Explain better." (in the new version, it is Fig.10 and Fig.11). It is not easy to find the plateau in Fig.9b. How did you do it? I do not see any explanation/reference to Fig. 11b in the text, and its description is insufficient.
6. It's a pity they didn't correct the conclusions to show better significance of content and novelty.

Author Response

Dear reviewer,

Thanks a lot for taking the time to review our work again. We regret any oversight in addressing your previous feedback properly, and we hope that we meet your expectations this time.

 

Here, below, we provide answers to your new comments with our responses.

 

Comment 1. “It would be valuable to include some of the comments from the "Cover Letter" that the authors sent me in the manuscript. The text would be easier for the reader to understand.”

Response 1. Dear reviewer,

We checked the previous “Cover letter” and tried to include all possible comments in the text of the manuscript. We hope that this will improve the understanding of the text. All changes are highlighted in yellow.

 

Comment 2. “It is enough to explain the abbreviations after his first use in the text.”

Response 2. Dear reviewer,

Thank you for this comment!

It is our serious mistake that some explanations appear twice in the text of the manuscript. We fixed it and highlighted all changes in yellow.

 

Comment 3. “What changes are in Table 1 apart from the reversed order compared to the previous version?”

Response 3. Dear reviewer,

Thank you for this question. One of the reviewers kindly asked us to reorder from low x values to high x values. We accepted this comment and corrected the typos. These are all the changes that we made to this table.

 

Comment 4. “Fig. 9b is very busy, and its caption is relatively poor”

Response 4. Dear reviewer,

Thank you for this comment. We tried to include some additional information in the caption of the Fig. 9b picture. Although we understand your comment, we cannot simplify the figure, since it shows important information about the frequency dispersion of the dielectric loss tangent of the samples. All changes are highlighted in yellow.

 

Comment 5. “I wrote:" Correct the caption to Fig.9 and Fig.10. Explain better." (in the new version, it is Fig.10 and Fig.11). It is not easy to find the plateau in Fig.9b. How did you do it? I do not see any explanation/reference to Fig. 11b in the text, and its description is insufficient.”

Response 5. Dear reviewer,

Thank you for this comment. Missing a reference to a figure in the text of the manuscript is a serious omission. We rewrote some sentences in the text and added references to Fig. 11b to correct this mistake. All changes are highlighted in yellow.

 

Comment 6. “It's a pity they didn't correct the conclusions to show better significance of content and novelty.”

Response 6. Dear reviewer,

Thank you for this comment. We corrected the “Conclusions” section and added sentences that show the significance of content and novelty.

Author Response File: Author Response.pdf