Phase Transition Behavior and Mechanical Properties of 9 Mol% CaO-PSZ with MnO₂ Doping Under Thermal Stress

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The topic of the article is relevant, since the use of oxide ceramics continues to expand due to their unique properties. Therefore, it would be good to expand the introductory part of the article and give examples of stabilization with other substances. The authors also ignored such an important issue as the assessment of the porous microstructure. After all, it is this factor that most affects the corrosion-mechanical properties of products.

Author Response

Dear referee,

Thank you for your precious compliments and comments to the manuscript titled “Phase Transition Behavior and Mechanical Properties of 9mol% CaO-PSZ with MnO₂ Doping under thermal stress”. The manuscript has been revised in accordance with your comments. The answers to your comments are listed as follows:

 

The topic of the article is relevant, since the use of oxide ceramics continues to expand due to their unique properties. Therefore, it would be good to expand the introductory part of the article and give examples of stabilization with other substances. The authors also ignored such an important issue as the assessment of the porous microstructure. After all, it is this factor that most affects the corrosion-mechanical properties of products.

Answer) Many thanks for your informative comment. As you suggested, we have now included examples of stabilizing agents used for ZrO₂ in the Introduction section of the revised manuscript and have provided supporting references. The following sentence has been added:

" Various doping strategies have been studied to improve the high-temperature mechanical properties of zirconia through the use of stabilizers such as Y₂O₃, MgO, Al₂O₃, Bi₂O₃, and CaO [11, 12]."

Regarding your comment on the evaluation of the porous microstructure, we agree that porosity can significantly affect both mechanical properties and erosion behavior. However, in this study, all specimens were fabricated simultaneously under identical conditions. As shown in Figures 3 and 9, the microstructure was carefully examined, and no visible pores were observed at the magnification used. Therefore, we believe that the evaluation of porosity is not a critical issue in the context of this manuscript.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

major revisions needed.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

The English could be improved to more clearly express the research.

Author Response

Dear referee,

Thank you for your precious compliments and comments to the manuscript titled “Phase Transition Behavior and Mechanical Properties of 9mol% CaO-PSZ with MnO2 Doping under thermal stress”. The manuscript has been revised in accordance with your comments. The answers to your comments are listed as follows:

 

1. The research proposal presented by the author is in accordance with “Aims & Scope” of Applied Sciences. Although the authors experimental research has already been widely investigated in the scientific community, with some similarities, the cubic phase fraction 2~3 mol% MnO₂ doping. After investigation, it has already been studied with some similarities. The authors must better justify the proposal for experimental research.

Answer) Thank you for your valuable comments. As you pointed out, most previous studies have focused on determining the optimal CaO doping level in ZrO₂ or investigating the effects of MnO₂ doping on phase stability. However, unlike these studies, our work systematically explores the co-doping of MnO₂ into CaO-doped ZrO₂.

In particular, we have mechanistically analyzed how changes in the oxidation state of the dopant ions, induced by MnO₂ co-doping in 9 mol% CaO-doped ZrO₂, affect phase stabilization and mechanical properties. This observation is distinct from what has been reported for single-doped ZrO₂. Furthermore, considering the practical applications in high-temperature environments, we systematically investigated the mechanical durability, phase evolution, and microstructural changes under thermal shock conditions (Δ400°C).

We believe that our study is distinguished from previous works not only by identifying the optimal co-doping combination of CaO and MnO₂, but also by experimentally elucidating the phase stabilization mechanism and the improvement of mechanical durability under thermal shock conditions.

This part has been revised and incorporated as the final sentence of the Introduction, as follows.

“This trend is expected to be different from that observed when ZrO₂ is doped solely with CaO or MnO₂. The effects of MnO₂ doping on the structural and mechanical properties of CSZ were then investigated before and after thermal shock to assess its durability under thermal stress.”

 

2. I present some questions that need to be clarified first. In order to maintain the quality of intellectual production and the review criteria required by Applied Sciences, plagiarism was investigated. 70% average plagiarism, 22% identical and 40% with minor changes.

Answer) I find this comment somewhat difficult to understand. To clarify, the current manuscript is based on a previous version that was submitted to the journal Metals in December 2024, but was later voluntarily withdrawn by the authors after determining that the data and analysis were insufficient.In this revised version, we have improved the interpretation of the XRD Rietveld analysis and enhanced the reliability of the data, as well as added supporting TEM analysis. Furthermore, we determined that the topic of this paper is more suitable for Applied Sciences, and thus decided to submit it to this journal.

We suspect that the similarity detected by plagiarism detection tools likely stems from overlap with our unpublished previous submission. We confirm that there was no intention of plagiarism or self-plagiarism. For transparency, we have attached the manuscript that was previously submitted to Metals.

 

3. Graphical results: Modulus of rupture data for twoMgO-ZrO2 alloys comparing the room-temperature MOR before and after thermal up-shock as a function of ageing time at temperature; Table: lattice parameters of the c- and t-phases after ageing at temperature; optical micrographs of Mg-CSZ showing the c- and m-phases after agei; Mg-CSZ material: bright-field TEM of very small matrix precipitates; selected-area electron diffraction pattern; effect of ageing on grain interiors; tetragonal precipitates in Mg - CSZ matrix after time ageing at temperature; bright-field TEM images showing the nucleation and growth of the decomposition products in Mg - CSZ; Crack in a decomposed region in Mg - CSZ (the copious crack-matrix/pipe interaction); sections of [112] SAD patterns showing 6-phase development resulting from temperature; Mg - PSZ material aged time, dark-field TEM image showing presence of f-phase in matrix regions between precipitates, two diffracted 6-phase beams; series of dark-field TEM images showing effect of temperature ageing on precipitates in Mg - PSZ; show an appendix: The one-dimensional (i.e. boundary length) Brooks’ analysis may be criticized on the basis that it is inadequate and a more rigorous three-dimensional (particule radius) approach, such as proposed (reference); equation derived by Potter and Heuer; show a table: volume fraction of monoclinic phase; equation of linear expansion coefficients; graphical: thermal expansion coefficient curves before and after post-heat treatment; table of the thermal expansion coefficient; the monoclinic phase fraction was double-checked for integrated intensity; equation of the volume fraction of the monoclinic phase.

Suggestion: Ca − PSZ by post-heat treatment (CaOx − ZrO2 x = 5 − 10 mol%); CaO (5CSZ − 10CSZ ); erosion of 2 − 4mol% CeO2 -doped CaO−stabilized zirconia; mechanical and thermal properties of zir- conia used in high-temperature environments by using compounds such as Y2O3, MgO, Al2O3, Bi2O3, and CaO as phase stabilizers; partially stabilized zirconia (PSZ) or fully stabilized zirconia (FSZ) at high temperatures; Ce4+ ions (97 pm) for Zr4+ ions (84 pm) in the lattice.

 

Answer) Thank you for your comment. I find it somewhat difficult to fully understand the details of your comment. I would appreciate it if you could clarify your points more specifically. Although I may not have fully understood your intention, I would like to provide my response to your comment as follows.

 Q. Modulus of rupture data for twoMgO-ZrO2 alloys comparing the room-temperature MOR before and after thermal up-shock as a function of ageing time at temperature.
 A. In this study, MnO₂ was doped into CaO-stabilized ZrO₂, and thus the material is not an alloy. Furthermore, the durability against thermal shock was comparatively evaluated by applying 40 cycles of △400°C thermal shock, depending on the amount of MnO₂ doping in CSZ. Therefore, the strength values as a function of ageing time are not directly related to the main characteristics investigated in this research.

 Q. Table: lattice parameters of the c- and t-phases after ageing at temperature
 A. The lattice parameters of cubic and tetragonal ZrO₂ are intrinsic values determined by their respective crystal structures, and do not change depending on the ageing temperature. Therefore, the observed lattice parameters depend on which phase is present in the sample. These results are shown in Figure 5 and Table 4.

 Q. Optical micrographs of Mg-CSZ showing the c- and m-phases after agei; Mg-CSZ material
 A. Optical microscopy only allows observation of the surface morphology of the material and does not provide information about specific phases such as cubic or monoclinic.

 Q. bright-field TEM of very small matrix precipitates; selected-area electron diffraction pattern; effect of ageing on grain interiors; tetragonal precipitates in Mg - CSZ matrix after time ageing at temperature; bright-field TEM images showing the nucleation and growth of the decomposition products in Mg - CSZ; Crack in a decomposed region in Mg - CSZ (the copious crack-matrix/pipe interaction); sections of [112] SAD patterns showing 6-phase development resulting from temperature; Mg - PSZ material aged time, dark-field TEM image showing presence of f-phase in matrix regions between precipitates, two diffracted 6-phase beams; series of dark-field TEM images showing effect of temperature ageing on precipitates in Mg - PSZ
 A. The precipitates and phase changes after thermal shock were identified using XRD, and the existence of the phases observed by XRD was further confirmed by determining the lattice parameters using TEM. According to the XRD analysis, no secondary phases or precipitates were detected. These results are presented in Figures 4 and 5.

Q. show an appendix: The one-dimensional (i.e. boundary length) Brooks’ analysis may be criticized on the basis that it is inadequate and a more rigorous three-dimensional (particule radius) approach, such as proposed (reference); equation derived by Potter and Heuer;
A. Thank you for your valuable suggestion. While the increase in grain size upon MnO₂ doping in CSZ was initially interpreted as an enhancement in sinterability, I have now incorporated the interpretation based on the critical grain size model proposed by Potter & Heuer. According to this model, MnO₂ doping increases the critical grain size, thereby stabilizing the tetragonal phase even at larger grain sizes. This explanation has been added to the description of Figure 3.

“Based on these microstructural observations, and according to the three-dimensional critical grain size model proposed by Potter and Heuer, the tetragonal-to-monoclinic phase transformation is governed by the relationship between the grain size and the critical grain size (rc​). where rc​ is the critical grain size (radius), γ is the interfacial energy, and ΔGv​ is the difference in volumetric free energy. MnO₂ doping not only significantly increased the average grain size (from 2–11 μm to 36–50 μm), but also dramatically reduced the monoclinic phase fraction (from 32.6% to 2.5–6.5%). This indicates that MnO₂ doping increases the critical grain size, thereby stabilizing the tetragonal phase even at much larger grain sizes. The observed decrease in monoclinic phase fraction with increasing MnO₂ content is therefore attributed to the increase in rc​ rather than a reduction in grain size.” Through this interpretation, the grain growth observed in MnO₂-doped CSZ can be explained more reliably.

 Q. show a table: volume fraction of monoclinic phase;
 A. The volume fraction of the monoclinic phase is presented in Tables 2 and 3.

 

 Q. equation of linear expansion coefficients; graphical: thermal expansion coefficient curves before and after post-heat treatment; table of the thermal expansion coefficient
 A. Thank you for your comment. The phase transformation behavior, mechanical properties, and thermal shock resistance of CaO-stabilized ZrO₂ doped with MnO₂ were evaluated. The coefficient of thermal expansion was not measured separately in this study. If you could provide more detailed comments or suggestions, we will consider measuring the coefficient of thermal expansion in the future.

 Q. the monoclinic phase fraction was double-checked for integrated intensity; equation of the volume fraction of the monoclinic phase.
 A. As described in the Materials and Methods section, the phase fractions were analyzed using the Rietveld refinement technique in the Highscore Plus software. The ICSD patterns of monoclinic ZrO₂ (m-ZrO₂, ICSD 98-006-0900), tetragonal ZrO₂ (t-ZrO₂, ICSD 98-007-0014), cubic ZrO₂ (c-ZrO₂, ICSD 98-064-7689), and MnO₂ (ICSD 98-000-0393) were used as references.

 

We have made comprehensive revisions to the English to improve expression and ensure clarity.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

In this manuscript, the authors investigate the phase stability, microstructure, and mechanical properties of MnO₂-doped 9 mol% CaO-stabilized zirconia (CSZ). As the MnO₂ content increases from 2% to 4%, the monoclinic phase fraction decreases significantly from 32.6% to 2.5%, while the tetragonal phase fraction rises from 58.2% to 90.3%. After careful consideration, I recommend major revision. The following comments are provided to guide the revision process:

1. In the introduction, the statements “MnO₂-doped 9 mol% CaO-stabilized zirconia (CSZ) was investigated in terms of phase stability, microstructure, and mechanical properties” and “their phase transition behavior, microstructure, and mechanical properties were evaluated before and after thermal cycling” appear overly redundant. This repetition suggests that the authors should revise for conciseness and clarity. Moreover, the abstract introduces detailed phase evolution with increasing MnO₂ content, but the descriptions are overly complex and may confuse readers. Simplification is recommended.
2. The cubic phase fraction is described as initially decreasing and then increasing; this trend should be clarified and supported with data. Additionally, the authors should explicitly identify the third phase present in MnO₂-doped CSZ.
3. The authors report a reduction in the monoclinic phase from 32.6% to 2.5%, and an increase in the tetragonal phase to 90.3%, suggesting phase stabilization comparable to fully stabilized ZrO₂. However, further discussion is warranted, particularly regarding the stabilization mechanism. The authors are encouraged to refer to relevant literature (e.g., DOI: 10.3390/mi15080938) to contextualize the phase transformation behavior.
4. Table 1 on Page 2 appears overly simplistic. It is recommended to include additional fabrication conditions and related properties (e.g., phase composition, microstructure, and mechanical performance) to enhance its usefulness.
5. Two separate tables titled “Table 1” appear on Pages 2 and 4, respectively. The authors should either merge these tables or clearly distinguish them with unique titles and numbers to avoid confusion.
6. In Figure 2c, the peak fitting appears inaccurate; there may be two overlapping peaks, particularly on the left side. This should be re-evaluated for correctness.
7. In Figure 5, lattice parameters such as “a” and “b” should be labeled with explicit numerical values. Additionally, the authors should confirm whether these values are consistent with those derived from XRD analysis?
8. In Figures 6 through 8, the “before” and “after” labels should be placed within the images rather than outside. Additionally, the label “sample” is unnecessary and can be removed for clarity.
9. The reference list contains inconsistencies, particularly in the capitalization of chemical formulas and material names (e.g., Ref. 14: CaOx-ZrO₂). All references should be carefully reviewed and formatted consistently according to journal guidelines.

Author Response

Dear referee,

Thank you for your precious compliments and comments to the manuscript titled “Phase Transition Behavior and Mechanical Properties of 9mol% CaO-PSZ with MnO₂ Doping under thermal stress”. The manuscript has been revised in accordance with your comments. The answers to your comments are listed as follows:

 

In this manuscript, the authors investigate the phase stability, microstructure, and mechanical properties of MnO₂-doped 9 mol% CaO-stabilized zirconia (CSZ). As the MnO₂ content increases from 2% to 4%, the monoclinic phase fraction decreases significantly from 32.6% to 2.5%, while the tetragonal phase fraction rises from 58.2% to 90.3%. After careful consideration, I recommend major revision. The following comments are provided to guide the revision process:

 

 

1. In the introduction, the statements “MnO₂-doped 9 mol% CaO-stabilized zirconia (CSZ) was investigated in terms of phase stability, microstructure, and mechanical properties” and “their phase transition behavior, microstructure, and mechanical properties were evaluated before and after thermal cycling” appear overly redundant. This repetition suggests that the authors should revise for conciseness and clarity. Moreover, the abstract introduces detailed phase evolution with increasing MnO₂ content, but the descriptions are overly complex and may confuse readers. Simplification is recommended.

 

Answer) We sincerely thank the reviewer for the helpful comments and suggestions. We would like to clarify that, although the reviewer mentioned the introduction, we believe the sentences in question are actually from the abstract. In response to the reviewer’s comments, we have revised the abstract to remove redundancy and improve clarity.

The original sentences, "MnO₂-doped 9 mol% CaO-stabilized zirconia (CSZ) was investigated in terms of phase stability, microstructure, and mechanical properties. 9 mol% CSZ samples were doped with 2–4 mol% MnO₂, and their phase transition behavior, microstructure, and mechanical properties were evaluated before and after thermal cycling," have been combined into a single, concise sentence:

"MnO₂-doped 9 mol% CaO-stabilized zirconia (CSZ) was investigated in terms of phase stability, microstructure, and mechanical properties before and after thermal cycling."

This revision was made to eliminate redundancy and improve the clarity of the manuscript.

Additionally, the sentences in the abstract describing the phase changes with increasing MnO₂ content were revised for clarity. The original text was:

"Increasing the MnO₂ content from 2 to 4 mol% resulted in a decrease in the monoclinic phase fraction from 32.6% to 2.5%, while the tetragonal phase fraction increased from 58.2% to 90.3%, indicating phase stabilization comparable to that of fully stabilized ZrO₂. The cubic phase fraction decreased from 9.2% to 3.4% with 2–3 mol% MnO₂ doping, but increased to 7.2% with 4 mol% doping. The 9 mol% CSZ showed a mixture of grains around 2 μm and 10 μm, while the MnO₂-doped CSZ exhibited only grains larger than 30 μm, which means that MnO₂ acted as a sintering aid. After thermal cycling, the monoclinic phase fraction increased from 7.8% to 17.2% as the MnO₂ doping level increased from 2 to 4 mol%, while the tetragonal phase fraction declined from 53.6% to 21.8%."

This was reorganized as follows for better readability:

"As the MnO₂ content increased from 2 to 4 mol%, the monoclinic phase fraction decreased significantly (32.6% to 2.5%), while the tetragonal phase fraction increased (58.2% to 90.3%), indicating enhanced phase stability comparable to fully stabilized ZrO₂. The cubic phase fraction decreased from 9.2% to 3.4% with 2–3 mol% MnO₂, but increased to 7.2% at 4 mol%. After thermal cycling, increasing the MnO₂ content from 2 to 4 mol% led to an increase in the monoclinic phase fraction (7.8% to 17.2%) and a decrease in the tetragonal phase fraction (53.6% to 21.8%)."

 

 

2. The cubic phase fraction is described as initially decreasing and then increasing; this trend should be clarified and supported with data. Additionally, the authors should explicitly identify the third phase present in MnO₂-doped CSZ.

 

Answer) The increase in the cubic phase fraction observed at 4 mol% MnO₂ doping is indeed related to the formation of oxygen vacancies. As shown in Figure 2 of our manuscript (XPS results), both Mn²⁺ and Mn³⁺ ions coexist in ZrO₂ at 2–3 mol% MnO₂ doping, whereas only Mn²⁺ is present at 4 mol% MnO₂ doping. This indicates that the concentration of oxygen vacancies is highest at 4 mol% MnO₂, which leads to an increase in the cubic phase fraction.

The stabilization process can be explained by crystal chemistry: oxygen vacancies associated with Zr can provide stability for cubic zirconia. Vacancies introduced by oversized dopants are located as the nearest neighbors to the Zr atoms, leaving the eightfold coordination to dopant cations. Undersized dopants compete with Zr ions for oxygen vacancies in zirconia, resulting in six-fold oxygen coordination and a large disturbance to the surrounding next nearest neighbors.

Furthermore, as shown in Tables 2 and 3, no third phase was observed before or after the thermal shock treatment. This further supports the conclusion that the observed changes in the cubic phase fraction are not due to the formation of a third phase, but are instead related to the generation of oxygen vacancies.

 

Relevant references supporting this mechanism are as follows:

1. Agarkov, D.A.; Borik, M.A.; Bredikhin, S.I.; Burmistrov, I.N.; Eliseeva, G.M.; Kolotygin, V.A.; Kulebyakin, A.V.; Kuritsyna, I.E.; Lomonova, E.E.; Milovich, F.O.; et al. Structure and transport properties of zirconia crystals co-doped by scandia, ceria and yttria. J. Mater. 2019.
2. Taylor, M.A.; Argirusis, C.; Kilo, M.; Borchardt, G.; Luther, K.-D.; Assmus, W. Correlation between ionic radius and cation diffusion in stabilised zirconia. Solid State Ion. 2004, 173, 51–56.
3. Mago, S.; Sharma, C.; Mehra, R.; Pandey, O.P.; Singh, K.L.; Singh, A.P. Preparation of YZT a mixed conductor by microwave processing: A different mechanism in the solid state thermochemical reaction. Mater. Chem. Phys. 2018, 216, 372–379.

 

 

 

 

3. The authors report a reduction in the monoclinic phase from 32.6% to 2.5%, and an increase in the tetragonal phase to 90.3%, suggesting phase stabilization comparable to fully stabilized ZrO₂. However, further discussion is warranted, particularly regarding the stabilization mechanism. The authors are encouraged to refer to relevant literature (e.g., DOI: 10.3390/mi15080938) to contextualize the phase transformation behavior.

 

Answer) The phase stabilization mechanism induced by MnO₂ doping can be explained mainly by two factors: the ionic radius of the dopant and the generation of oxygen vacancies.

First, the size effect plays an important role. While Ca²⁺ ions have a larger ionic radius than Zr⁴⁺ ions, Mn²⁺ and Mn³⁺ ions are smaller than Zr⁴⁺. The difference in ionic radii between the dopant ions and Zr⁴⁺ causes lattice distortion, which contributes to the stabilization of the high-temperature phases (tetragonal or cubic) at room temperature.

Second, MnO₂ doping also leads to the formation of additional oxygen vacancies in the ZrO₂ lattice. These oxygen vacancies further destabilize the monoclinic phase and promote the stabilization of the tetragonal or cubic phases.

Therefore, MnO₂ doping in ZrO₂ not only increases the concentration of oxygen vacancies but also introduces lattice distortion due to the difference in ionic radii between the dopant and host ions. Both effects synergistically contribute to the significant phase stabilization observed in our results.

The original explanation was:

"This may result in better stabilization compared to Ca²⁺ (1.00 Å), because the ionic radii of Mn²⁺ (0.83 Å) and Mn³⁺ (0.65 Å) are smaller than those of Ca²⁺ (1.00 Å) and Zr⁴⁺ (0.84 Å). This larger difference in ionic radii is believed to cause increased lattice distortion when substitutional solid solutions are formed."

This has been revised and expanded for greater detail as follows:

"Ca²⁺ ions (1.00 Å) are larger than Zr⁴⁺ ions (0.84 Å), whereas Mn²⁺ (0.83 Å) and Mn³⁺ (0.65 Å) ions are smaller than Zr⁴⁺ ions. These differences in ionic radii lead to lattice contraction and distortion, which play a significant role in phase stabilization. MnO₂ doping in ZrO₂ not only generates additional oxygen vacancies but also enhances phase stabilization through the lattice distortion caused by the contraction of the lattice due to the smaller dopant ions. Therefore, both the increased concentration of oxygen vacancies and the size effect of the dopant ions synergistically contribute to the stabilization of the tetragonal phase."

 

 

 

4. Table 1 on Page 2 appears overly simplistic. It is recommended to include additional fabrication conditions and related properties (e.g., phase composition, microstructure, and mechanical performance) to enhance its usefulness.

 

Answer) In response, we have added the fabrication conditions (calcination temperature and holding time) to Table 1 as you suggested. Since Table 1 describes the synthesis conditions of the powders, we did not include microstructure or mechanical properties. Accordingly, we have also modified the caption of Table 1 to "Compositions and fabrication conditions of 9CSZ specimens with varying MnO₂ content" to better reflect its contents.

 

 

 

 

5. Two separate tables titled “Table 1” appear on Pages 2 and 4, respectively. The authors should either merge these tables or clearly distinguish them with unique titles and numbers to avoid confusion.

Answer) Thank you for your helpful comment. We have corrected all the table numbers and updated them accordingly in the main text.

 

 

 

6. In Figure 2c, the peak fitting appears inaccurate; there may be two overlapping peaks, particularly on the left side. This should be re-evaluated for correctness.

Answer) Thank you very much for your important comment. As you pointed out, the fitting on the higher energy side of Figure 2C does not appear to be perfect. Therefore, we have re-evaluated the accuracy of the fitting as follows.

The purpose of the XPS analysis shown in Figure 2 is to determine the valence state of the Mn ions doped into ZrO₂. Accordingly, we examined the possible valence states of Mn ions, namely Mn²⁺, Mn³⁺, and Mn⁴⁺.

As shown in Figure A, the current fitting in Figure 2C considers only Mn²⁺, and although there is a slight mismatch around 642–646 eV, the residual standard deviation (STD) is below 2, which indicates a reliable fitting.

 

Figure A. Mn 2p XPS Spectrum Fitting without Mn³⁺ and Mn⁴⁺

As illustrated in Figure B, when both Mn³⁺ and Mn⁴⁺ were considered in the fitting, the residual STD was also below 2, indicating a reliable result, and the fitting quality was even better than when only Mn²⁺ was considered. However, the newly introduced peak at 644 eV deviates significantly from the reported value of 643 eV for Mn⁴⁺, suggesting that this is not a correct fitting result. Therefore, we believe that it is more appropriate to exclude Mn⁴⁺ when discussing the valence state of Mn ions based on this data.

In conclusion, for the purpose of identifying the valence state of Mn ions present in CSZ, we believe that the fitting results excluding Mn³⁺ and Mn⁴⁺ are more appropriate.

 

Figure B. Mn 2p XPS Spectrum Fitting with Mn³⁺ and Mn⁴⁺

It is possible that the fitting quality was affected by the presence of other ions besides Mn ions; however, since this is beyond the scope of the present study, we did not consider it further.

7. In Figure 5, lattice parameters such as “a” and “b” should be labeled with explicit numerical values. Additionally, the authors should confirm whether these values are consistent with those derived from XRD analysis?

Answer) The quantitative values of the lattice parameters indicated as "a" and "b" in Figure 5 are provided in Table 4. The lattice parameters obtained from the XRD results represent those of the entire unit cell. As you are aware, when observing the crystal structure using TEM, it is not possible to focus on a single specific plane, and various crystallographic orientations can be observed. Therefore, we referred to the lattice parameter values for each plane as reported in references 21 and 22, as well as ICSD 98-001-5983. Based on these references, we cross-checked the presence of the phases identified in the XRD results.

 

 

8. In Figures 6 through 8, the “before” and “after” labels should be placed within the images rather than outside. Additionally, the label “sample” is unnecessary and can be removed for clarity.

Answer) We have revised Figures 6 to 8 accordingly, taking your suggestions into consideration.

 

 

9. The reference list contains inconsistencies, particularly in the capitalization of chemical formulas and material names (e.g., Ref. 14: CaOx-ZrO₂). All references should be carefully reviewed and formatted consistently according to journal guidelines.

Answer) We have carefully revised the subscripts and capitalization of chemical formulas and material names in the reference list according to the journal guidelines.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors answered all questions. I recommend the publication.

Comments for author File: Comments.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have addressed my previous comments point by point; therefore, it can be now accepted in current form.