Two Perovskite Modifications of BiFe0.6Mn0.4O3 Prepared by High-Pressure and Post-Synthesis Annealing at Ambient Pressure
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsInteresting work, the paper presents a thorough and well-conducted study on the structural and magnetic properties of BiFe0.6Mn0.4O3 modifications. Addressing the specific suggestions mentioned above could enhance the clarity and impact of the manuscript. However, there are some concerns need to be address before any publication:
1. There is lack of comparison between this modification with other modification methods such as plasma (low and atmospheric pressure?), chemical methods, etc. There should be some data like that where the reader can find what is the advantage and disadvantage of their approach compared to others.
2. The paper does not adequately compare these results with pristine BiFeO3. This comparison is crucial to highlight the specific impact of Mn doping on the structural and magnetic properties.
3. It is unclear the setup of the experiment. And it would be so helpful for the reader to Provide a brief rationale for the specific synthesis conditions chosen. The description of the synthesis procedures lacks sufficient detail about the conditions and parameters. For example, the exact pressure and temperature ranges for high-pressure synthesis, and the duration of annealing at ambient pressure, are not thoroughly explained. This makes reproducibility difficult for other researchers.
4. The discussion on thermal stability and phase transformation lacks a detailed mechanism. Explaining the atomic-level changes or providing a thermodynamic analysis of the phase stability would give a deeper understanding of the observed phenomena.
5. The mechanism behind the conversion polymorphism observed when the HP phase transforms to the AP phase upon heating is not thoroughly explained. Providing a more detailed discussion on the possible atomic rearrangements or phase transition pathways would enhance the understanding of this phenomenon.
6. A suggestion (not so crucial): The scalability of the high-pressure synthesis method is not addressed. For practical applications, it is essential to discuss whether the synthesis process can be scaled up and if the results are reproducible on a larger scale.
Comments on the Quality of English Language
The English language of the paper is fine.
Author Response
Reviewer 1.
- There is lack of comparison between this modification with other modification methods such as plasma (low and atmospheric pressure?), chemical methods, etc. There should be some data like that where the reader can find what is the advantage and disadvantage of their approach compared to others.
Our reply.
As the reviewer mentioned, different methods of the preparation of Bi1-xRxFeO3 and BiFe1-xMxO3 were developed and used in the literature. However, our paper is focused on one member of the BiFe1-xMnxO3 solid solutions. Therefore, we focused our introduction and discussion on this system. In the case of BiFe1-xMnxO3 solid solutions, only a standard solid-state synthesis in different atmospheres and high-pressure high-temperature methods were described in the literature. Therefore, we cannot compare a lot of different preparation methods for the BiFe1-xMnxO3 solid solutions. In the revised introduction of our manuscript, we added the following paragraph:
“During two decades of intensive research on BiFeO3-related materials different preparation methods of Bi1-xRxFeO3 and BiFe1-xMxO3 were developed and used, for example, different modifications of a standard solid-state synthesis (e.g., rapid synthesis) in different atmospheres, high-pressure (HP) high-temperature methods, variable soft-chemistry ways, plasma syntheses, and so on. However, in the case of BiFe1-xMnxO3 solid solutions, only a standard solid-state synthesis in different atmospheres and HP high-temperature methods were described in the literature.”
- The paper does not adequately compare these results with pristine BiFeO3. This comparison is crucial to highlight the specific impact of Mn doping on the structural and magnetic properties.
Our reply.
We thank the reviewer for this advice. In the revised manuscript in the end of part 2, we added the following paragraph:
“The introduction of Mn3+ cations into BiFeO3 changes the crystal structure from a certain concentration of Mn3+ cations due to the existence of several competing structures and monotonically suppresses TN from 643 K in BiFeO3 to about 270 K in BiFe0.5Mn0.5O3 [17, 24, 25]. Magnetic transition temperatures of BiFe1-xMnxO3 remain relatively high because of large concentrations of Fe3+ cations. Magnetic properties of BiFeO3 [17] and AP-BiFe0.6Mn0.4O3 were qualitatively similar in a sense that they both show nearly pure AFM behavior despite their different crystal structures. Temperature dependence of magnetic susceptibility exhibits a sharp rise just below TN in both compounds indicating an initial development of uncompensated moments, but these uncompensated moments are suppressed at lower temperatures.”
- It is unclear the setup of the experiment. And it would be so helpful for the reader to Provide a brief rationale for the specific synthesis conditions chosen. The description of the synthesis procedures lacks sufficient detail about the conditions and parameters. For example, the exact pressure and temperature ranges for high-pressure synthesis, and the duration of annealing at ambient pressure, are not thoroughly explained. This makes reproducibility difficult for other researchers.
Our reply.
The synthesis and experimental procedures are described in details in part 3. In particular, we gave the synthesis pressure, temperature, time. For the ambient-pressure modification, temperature, annealing time, heating/cooling rate were reported as “The AP modification of BiFe0.6Mn0.4O3 was prepared by heating HP-BiFe0.6Mn0.4O3 in air at AP at 773 K for 10 min (with a heating-cooling rate of 10 K/min).”. Therefore, experimental procedures can be reproduced. In the revised manuscript in part 3, we added the following paragraph related to specific synthesis conditions chosen:
“As the used synthesis conditions for HP-BiFe0.6Mn0.4O3 gave high-quality samples, we did not investigate effects of synthesis conditions on the quality of HP-BiFe0.6Mn0.4O3 and pressure-temperature stability ranges of HP-BiFe0.6Mn0.4O3 (it was also out of the scope of the present work). But we note that pressure-temperature stability ranges of BiFe1-xMnxO3 solid solutions could be relatively large as lower pressure of 5 GPa and lower temperature of 1073 K was used in the literature [25].”
- The discussion on thermal stability and phase transformation lacks a detailed mechanism. Explaining the atomic-level changes or providing a thermodynamic analysis of the phase stability would give a deeper understanding of the observed phenomena.
- The mechanism behind the conversion polymorphism observed when the HP phase transforms to the AP phase upon heating is not thoroughly explained. Providing a more detailed discussion on the possible atomic rearrangements or phase transition pathways would enhance the understanding of this phenomenon.
Our reply.
We thank the reviewer for this advice. In the revised manuscript, we added a new figure with the presentation of crystal structures and the following paragraph:
“Figure 6 shows crystal structures of HP-BiFe0.6Mn0.4O3, AP-BiFe0.6Mn0.4O3, and PbZrO3 (at room temperature) for comparison [28]. (FeMn)O6 octahedra are strongly distorted in both modifications; the similar effect is observed for TiO6 octahedra in PbZrO3. These features can be explained by the formation of strong covalent Bi–O and Pb–O bonds originating from stereochemical activity of the lone pair of Bi3+ and Pb2+ cations. In other words, elongated (FeMn)–O or Zr–O bonds are simultaneously involved in short Bi–O or Pb–O bonds, respectively [17]. The HP synthesis method usually stabilizes a modification with higher density. Density of HP-BiFe0.6Mn0.4O3 (8.439 g/cm3) was indeed slightly higher than that of AP-BiFe0.6Mn0.4O3 (8.418 g/cm3) (Tables 1 and 2). To achieve higher density and to accommodate the lone pair of Bi3+, an additional octahedral rotation along the b axis was probably necessary (Figure 6c) resulting in a superstructure and a stressed structure in HP-BiFe0.6Mn0.4O3. Heating at AP results in the release of stress. The transformation of HP-BiFe0.6Mn0.4O3 into AP-BiFe0.6Mn0.4O3 involves small rotations of (FeMn)O6 octahedra (Figures 6b and 6c) and small shifts of Bi3+ cations.”
- A suggestion (not so crucial): The scalability of the high-pressure synthesis method is not addressed. For practical applications, it is essential to discuss whether the synthesis process can be scaled up and if the results are reproducible on a larger scale.
Our reply.
We believe that the scalability of the high-pressure synthesis has intrinsic restrictions. It depends on the size of high-pressure machines and the size of used high-pressure cells. There are large high-pressure machines (which are used, for example, for the industrial growth of diamonds). However, we do not have access to such large high-pressure machines to check the scalability. We are using laboratory-size high-pressure machines. Therefore, the size of samples has intrinsic restrictions and cannot be changed.
The second reviewer said “English language fine. No issues detected”.
The first reviewer said in the end of the review “The English language of the paper is fine”. Therefore, we believe that the first reviewer marked the field “The English is very difficult to understand/incomprehensible” by mistake.
Reviewer 2 Report
Comments and Suggestions for AuthorsMost of the compositions of the perovskite BiFeO3-BiMnO3 system including BiMnO3 end member require high pressure synthesis, which is a quite exotic method. Nevertheless, this system is one the most studied by now among the BiFeO3-derived solutions with substitutions at the Fe site. Therefore it is a good surprise to know that researchers continue to discover new properties and effects in the BiFeO3-BiMnO3 solutions.
The paper is very clear and convincing. The results and conclusions are based on the high-quality measurements followed by the detailed analysis.
Author Response
We thank the reviewer 2 for positive evaluation of our paper.
No comments were given.
