On Thermodynamic Aspects of Oxide Crystal Growth

Round 1

Reviewer 1 Report

The author conducted the research on “Thermodynamic aspects of oxide crystal growth” This work is very interesting, and it is also clearly presented. This paper is suitable to be considered for the publication after the several following issues are addressed. I recommend the minor revision of this work.

1. Please further revie the abstract part. It is more important to give the most information of this work there.
2. Transition metal oxides have been widely investigated as high temperature ion electro conductor. Please update some very important/landmark references into introduction part.

Matter, https://doi.org/10.1016/j.matt.2021.02.019;

Science of the total environment, https://doi.org/10.1016/j.scitotenv.2021.151213;

Separation and Purification Technology, https://doi.org/10.1016/j.seppur.2020.118295 ;

Journal of Membrane Science, https://doi.org/10.1016/j.memsci.2019.117180;

Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.07.209.

3. The English writing of this manuscript should be intensively improved, the help from senior researcher/scientist is recommended to further improve it. There are still some minor mistakes in the manuscript.
4. Take care that "spaces are required between characters".

Author Response

We are thankful for the detailed and helpful comments of the reviewer, and follow their recommendations:

• The abstract is longer and more detailed now.
• The 5 new references are included in the introduction now; additionally, two of them are mentioned in subsection 3.2 (V-Mo oxides).
• The writing is updated to our best, and hopefully improved.
• We wrote the text with the LaTeX style file provided by the journal. Thus, spacing and other formattion is mainly done by the stylefile automatically.
• The whole text (writing) is re-checked.

Reviewer 2 Report

This paper presented by Klimm et al. describes the mechanism of oxide crystals growth from a melt. They have taken a model example from calcium ferrite (Ca₂Fe₂O₅). They have also concluded that the crystallization is strongly affected by absorption of free O₂ from ambient atmosphere or by the release of O₂. In their study they have used DTA/TG analytical method for proof of concept. Additionally, the average valence state of these oxides can be different in the molten and  solid state.  I believe this work is very interesting and has a sound impact on material science and metallurgy. I have definitely enjoyed reading this work. However, for this work to be published the authors need to perform some minor revisions.

1. Line 13: “in” is missing. “in 1953”
2. Line 17: e.g., using the Czochralski, Bridgman, or float-zone methods: References needed
3. Lines (20-23): These materials have in common, that in all practically used atmospheres ranging from air to “pure” argon or nitrogen with ca. 99.9. . . 99.999% purity, the constituent metal cations prevail almost completely in one oxidation state. These are here Ca2+, W6+, Li+, Nb5+, Y3+, or Al3+ 23 , respectively. This sentence is poorly written. Please rewrite.
4. Line 38: The following materials that exhibit similar behavior to olivine is aegirine. The following reference should be cited: https://pubs.acs.org/doi/abs/10.1021/acsanm.8b01472
5. Line 69: optical float zone (OFZ) should be briefly explained to the reader
6. I wonder why the authors do not involve calculations of chemical potentials (Gibbs Free energies) for their melt/solid phase. Can the authors further elaborate on this ?
7. The English language of the paper can be further improved and the discussion written in a more chronological order.

Author Response

Dear Reviewer,

we are thankful for your positive comments, and handled your recommendations accordingly:

1. "in" is added.
2. Because this are best established methods of crystal growth, reference to corresponding chapters in the "Handbook of Crystal Growth" from Elsevier is given [2,3].
3. The sentence is splitter now into two sentences; and this way better readable.
4. We did not know this, thank you for the hint. Aegirine and the reference are added now as [13].
5. OFZ is explained shortly in the text, and again reference [3] is added.
6. Inclusion of the Gibbs energy G seemed us not so straightforward, because  certainly we observe just a crossover from low T (were G for the solid is lower) to high T (were G for the liquid phase is lower). Anyway: one can learn from this. We included 3 numbers in Fig. 3. First, G is given for both cases at the point were the system is just molten. There, of curse G(liq) = G(sol). Besides, we added the G value for the "red" system at the same T=1440°C, where the "blue" system is just molten. Here, the difference expresses the thermochemical difference between both systems.
7. We have done our best the review the text, and improve writing.