Skull Melting Growth and Characterization of (ZrO2)0.89(Sc2O3)0.1(CeO2)0.01 Crystals
, Mikhail Borik 3, Galina Eliseeva 1, Alexey Kulebyakin 3, Elena Lomonova 3, Filipp Milovich 3,4,*, Valentina Myzina 3, Yuriy Parkhomenko 4,5, Elena Skryleva 4 and Nataliya Tabachkova 3,4Round 1
Reviewer 1 Report
Comments for author File: 
Comments.pdf
Author Response
Reviewers' comments:
Reviewer #1: It is a very nice manuscript, which I found well addressed and nicely discussed. Appropriate to be recommended for publication in Crystals, as I propose to do.
I have only two minor suggestions:
Where is said ‘as-grown’ it should be said ‘as grown’.
Done
I also propose to authors replace the entry ‘4. Summary’ be the most realistic form ‘4. Concluding remarks’.
Done
Author Response File: 
Author Response.docx
Reviewer 2 Report
The manuscript exhibits experimental data on (ZrO2)0.89(Sc2O3)0.1(CeO2)0.01 crystals growth by means of directional melt crystallization in a cold crucible. Crystals obtained have been characterized using energy dispersion X-ray spectroscopy, Raman scattering spectroscopy, transmission electron microscopy and X-ray photoelectron emission techniques. This work corresponds to the Journal aims and scopes and provides a useful path for the readers. However, there are several major issues that the authors need to address. Below are comments and suggestions.
Point 1.
As it is mentioned in the “Introduction” section only cubic phase of ZrO2-Sc2O3-CeO2 system demonstrates the highest conductivity. Whereas the presence of rhombohedral ß-phase leads to significant decreasing in ionic conductivity. Also, the authors highlight that directional melt crystallization does not provide single-phase cubic solids, although this technique has been used for further ZrO2-Sc2O3-CeO2 crystal growth. In this connection it would be useful to demonstrate briefly the impact or/and significance of your present research for the scientific community and for potential applications.
Point 2.
The growth conditions seem to be confused. It would be useful to clarify following aspects for better understanding:
-the thermal range of cubic phase existence based on literature data with corresponding references or/and your own experimental data;
-explain the choice of the temperature range (from 3000 to 200 °C) for crystal growth;
-why initially, at cooling from 3000℃ to 2000℃, the cooling rate was 6-7 times higher than for 1000-200 ℃ temperature interval.
Point 3.
Lines 190-191 “…observed phase composition inhomogeneity in the crystal length can be the inhomogeneous overall ceria, Се3+ ions and scandia concentrations as shown above”. Although above the authors mentioned twice that “In the meantime the scandia concentration decreases along the crystal.” (lines 132 and 144). Please specify with the sufficient clarity the distribution character of scandium. Also it would be useful to provide a model described joint distribution of cerium, scandium and cubic/rhombohedral phases.
Author Response
Reviewers' comments:
Reviewer #2: The manuscript exhibits experimental data on (ZrO2)0.89(Sc2O3)0.1(CeO2)0.01 crystals growth by means of directional melt crystallization in a cold crucible. Crystals obtained have been characterized using energy dispersion X-ray spectroscopy, Raman scattering spectroscopy, transmission electron microscopy and X-ray photoelectron emission techniques. This work corresponds to the Journal aims and scopes and provides a useful path for the readers. However, there are several major issues that the authors need to address. Below are comments and suggestions.
Point 1.
As it is mentioned in the “Introduction” section only cubic phase of ZrO2-Sc2O3-CeO2 system demonstrates the highest conductivity. Whereas the presence of rhombohedral ß-phase leads to significant decreasing in ionic conductivity. Also, the authors highlight that directional melt crystallization does not provide single-phase cubic solids, although this technique has been used for further ZrO2-Sc2O3-CeO2 crystal growth. In this connection it would be useful to demonstrate briefly the impact or/and significance of your present research for the scientific community and for potential applications.
The presence of a low-temperature rhombohedral phase reduces the conductivity of crystals only at low temperatures (below ~ 600 °C), but practically does not affect the high-temperature conductivity.
The most promising composition in the ZrO2-Sc2O3-СеО2 system is the one containing 10 mol.% of Sc2O3 and 1 mol.% of СеО2 (10Sc1CeSZ), therefore, we wanted to investigate the factors affecting the formation of the crystal structure with this synthesis method, in this work. The study of crystals obtained by directional crystallization of the melt, makes it possible to study the fundamental properties of the material, excluding processes associated with the presence of grain boundaries in ceramic materials. The results obtained on crystals can be used to assess the stability of the phase composition and assess the contribution of grain boundaries to stabilization of a solid solution.
Point 2.
The growth conditions seem to be confused. It would be useful to clarify following aspects for better understanding:
-the thermal range of cubic phase existence based on literature data with corresponding references or/and your own experimental data;
-explain the choice of the temperature range (from 3000 to 200 °C) for crystal growth;
-why initially, at cooling from 3000℃ to 2000℃, the cooling rate was 6-7 times higher than for 1000-200 ℃ temperature interval.
The data on the cubic phase with the corresponding link is added to the article in the Results and Discussion section in accordance with your recommendation.
Melting point was close to 3000 °C for this material. Crystal growth occurs as the crystallization front moves at a speed of 10 mm / hour.
A feature of crystal growth by this method is the impossibility of post-growth annealing without the use of additional heat sources. Direct high-frequency heating of the material is used in this method, and not of the crucible in which the melt is located, and the possibility of heating the material and controlling the temperature of the melt depends on its electrical conductivity. The ingot of the crystallized melt cools down upon completion of the crystallization process as the container with the melt is removed from the heating zone (i.e., below the inductor zone) and heating by the high-frequency field ceases due to a decrease in the electrical conductivity of the material. Therefore, after the end of the process of directed crystallization of the melt, the crystallized melt spontaneously cools. The rate of further cooling is determined by the mass of crystallized melt. The text has been amended.
Point 3.
Lines 190-191 “…observed phase composition inhomogeneity in the crystal length can be the inhomogeneous overall ceria, Се3+ ions and scandia concentrations as shown above”. Although above the authors mentioned twice that “In the meantime the scandia concentration decreases along the crystal.” (lines 132 and 144). Please specify with the sufficient clarity the distribution character of scandium. Also it would be useful to provide a model described joint distribution of cerium, scandium and cubic/rhombohedral phases.
Sorry, but we didn’t quite understand the question. In our opinion, there is no contradiction in the given fragment of the text. As follows from Fig. 2, the concentration of scandium oxide decreases along the length of the crystal. A qualitative change in the rhombohedral phase along the length of the crystal can be judged by Raman spectra (Fig. 3a), but quantifying this is not possible.
Editorial Office`s Comments
We reformulated some fragments of the text that coincide with previous publications.
Round 2
Reviewer 2 Report
The authors gave detailed comments to the questions. Corresponding corrections have been made. The manuscript can be published in the Journal in present form.
Author Response
Reviewers' comments:
Point 3.
Lines 190-191 “…observed phase composition inhomogeneity in the crystal length can be the inhomogeneous overall ceria, Се3+ ions and scandia concentrations as shown above”. Although above the authors mentioned twice that “In the meantime the scandia concentration decreases along the crystal.” (lines 132 and 144). Please specify with the sufficient clarity the distribution character of scandium. Also it would be useful to provide a model described joint distribution of cerium, scandium and cubic/rhombohedral phases.
Dear Reviewers
We rewrite the problematic sentence at line 198. We changed the sentence on (The observed inhomogeneous distribution of the rhombohedral phase along the crystal length may be due to changes in the chemical composition along the crystal length, namely, changes in the total content of сeriа, changes in the ratio of Се3+/ Се4+, and changes in the scandiа content.)
