Studies on δ-Bi2O3 Based Nanocrystalline Glass-Ceramics Stabilized at Room Temperature by Novel Methods
Round 1
Reviewer 1 Report
The authors studied the synthesis of δ-Bi2O3 via twin-rollers and free cooling methods starting from the molten state. They investigate structure and microstructure using XRD, SEM and IS methods. Although the conclusions are reasonably supported by experimental evidence, the characterization of the data and relative discussions are rather limited. Results are of interest for readers of Applied Sciences journal but the English requires some improvement. Before considering for publication the authors should improve the English (see detailed criticisms below) and provide a more complete discussion of the results. Some additional literature reference may also be beneficial to provide a more complete context to potential readers.
Detailed Criticisms:
Title:
- Change “to room temperature” with “at room temperature”
Abstract:
- Line 11: Change “... , was ...” with “were”
- Line 11: “XRD” has to be defined “X-ray diffraction (XRD)”
- Line 15: Change “... , played Si and Al ...” with “... , was played by Si and Al ...”
Introduction
- Line 24: Change “... crystallographic systems ...” with “... structures ...”
- Line 25: Change “... . Materials of this type have so far been thoroughly ...” with “... . These materials were ...”
- Line 27-29: Provide some specific example for the material of study and or specific references were examples have been reported.
- Line 53: “... grain reduction ...” what do you mean? Rephrase it
Methods
- Line 65, 66: “Then, in the case of slow cooling the material was cooled freely with the furnace.” Provide additional details: cooling for how much time or till achieving what temperature? What was the temperature of the environment?
- Line 67, 68: Was the temperature of the roller controlled? What material were made of the rollers?
- Line 69: “As-received materials ...” do you mean the final products?
- Line 73: Why do you use the Sherrer equation after performing Rietveld refinement with GSAS-II? Don’t you have a better estimation of size and microstrain from the refinement?
- Line 76: XRD measurements were performed with what type of radiation (Cu?) and geometry (Bragg-Brentano? Flat sample?)?
- Line 78: “... refine the determination ...” What do you mean? Rephrase
- Line 88: change “... the thus pepared ...” with “... the sample ...”
Results
- Line 91-97: the same information is repeated right after in Line 99-102. Consider avoid the repetition. Rephrase accordingly.
- Line 103: “amorphous halo” this is not a proper definition. Do you mean “amorphous contribution to the scattering profile emerging from the background”? Rephrase.
- Line 106-108: This looks a strange way to state that the diffraction patter is different or that the reflection sequence is changed. Rephrase.
- Line 114: change “... , it can be claimed ...” with “..., it suggests ...”
- Line 138: “A disparity in the size ratio of the Bragg reflections ...” what do you mean? What is the size of a Bragg reflection? Clarify
- Line 159: “As expected, free cooling method produced polycrystalline materials” At this stage of the text it has not been provided any suggestion of the polycrystalline microstructure. Rephrase, explain.
- Line 173 (Figure 3): Are the heating and cooling done after the synthesis (i.e., after a first cooling)? Explain / clarify in detail the thermal treatment.
- Line 197: the word “structure” is used improperly. Cracks and pores appears in the microstructure.
- Line 198: what do you mean with not defined boundary?
- Line 198, 200: “... do not have clearly defined boundaries, which probably confirms the significant contribution of the amorphous matrix in the structure of the glass-ceramic composite, revealed in the XRD results as amorphous halo. ...”. grain boundary contributions to the diffracted signal would not be visible as a distinct component. The amorphous component (the “halo”) has to come from the matrix as an independent phase.
- Line 227-229: “... . The large sample inhomogeneity described earlier, which may significantly affects the shape of the diffractograms, is most likely responsible for such a remarkable discrepancy. ...” This statement sounds wrong. The grain size measured from SEM refers to the polycrystalline grains. XRD provides the size of the coherent crystalline domains which is reasonably smaller given the polycrystalline microstructure.
- Line 237-239: Impurities account for about 10%. This is quite significant. Are you sure it is still reasonable assume the Bi2O3molecule composition?
Discussion
- Line 268-278: these statements do not appear to discuss any of the results. Consider to move these in the conclusions section.
Conclusions
- Line 292-301: these statements appear to be more a discussion. Consider to slight rephrase and move in the discussion section.
References
- Extend the set of references used to provide a wider context for the discussed work. See, as an example, Nature Materials 14 (2015) 500.
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
1. General remarks
English is recommended to be checked.
There are several editing errors (punctuations, use of space), redundant words/expressions, or hard-to-follow sentences in the text, these are highlighted with yellow in the reviewed manuscript.
The reference list has some editing mistakes.
2. Comments to the Abstract & Introduction:
Lines 14-16: Revise the sentence
Line 25: “Materials of this type have” – specify, which type of material listed in the previous sentence this applies to
3. Comments to the Abstract & Introduction:
Why these temperatures were selected?
4. Comments to Results:
XRD patterns: peaks should be identified
Line 132: define/describe, what is the Rwp coefficient
Lines 135-138: “there are visible reflections which cannot be attributed to the δ-type phase, but their intensity is too low to reliably identify the additional crystalline phase, and more than that, their intensity is lower for higher melting temperature.” – Identify these peaks on the relevant figures
Figure 2.: dimensions are not marked
Lines 153-154: “a monoclinic phase (α) (calculation based on ICDD no. 00–041–1449) was identified” – Identify these peaks on the relevant figures
Lines 175-176: “it was found that a δ-type phase stabilized at room temperature recrystallizes to a γ-like phase (identification based on ICDD no. 00–045–1344)” – Identify these peaks on the relevant figures
Use SEM micrographs instead of SEM images/microphotographs, the former is closer to the academic language.
Figure 5: Words of the axis labels should not be capitalized, except the first word of the sentence
Comments for author File: Comments.pdf
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
This paper deals with the possibility to prepare nanocrystalline, stable at room temperature δ-Bi2O3 phase by twin-rollers and free cooling methods. The obtained product was studied by XRD, SEM, EDX and impedance spectroscopy. It was written nicely and I think that it will be of interest to the readership of Applied sciences, but certain points must be taken into account prior to publishing:
1. the authors must distinct the difference between grain size and crystallite size. The value obtained from XRD is the crystallite size, while the one obtained from the SEM is the grain size. These two terms are different. Grain can consist of several crystallites. This must be corrected in the manuscript.
2. As authors claim themselves, Scherrer method is poor and quite unprecise. Since the Rietveld analysis was already performed, I don't understand why the size-strain analyisis within Rietveld refinement wasn't performed? This should be done, and the results should be added to the manuscript.
3. Same goes for the amount of amorphous phase, why wasn't it determined? It seems like a very important information to me, and should be done. Especially because it is quite trivial to calculate within Rietveld refinement.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
