Pressure-Induced Structural Phase Transition and Metallization in Ga2Se3 Up to 40.2 GPa under Non-Hydrostatic and Hydrostatic Environments
Round 1
Reviewer 1 Report
The main problem in this paper is the study done in Raman. The authors need to explain where the assignments of the different peaks come from. The active Raman modes for F-4 3 m for 4a and 4c positions (Ga and Se respectively) are T2 (or F2). A' or A1 not correspond with this symmetry. There are some publications with the same notation but they are wrong.
Other suggestions are:
lines 53-55: Give crystallographic information for the different structures (space group, IT, unit cell parameters)
line: 78: Give the standard devistions for cell parameters. Including them in the Figure1
line 134: In Raman study was used only one hydrostatic environment not several....
What criteria are you using to say that the medium is hydrostatic in Raman studies?
Author Response
Response to Reviewer 1 Comments
Point 1: The main problem in this paper is the study done in Raman. The authors need to explain where the assignments of the different peaks come from. The active Raman modes for F-43 m for 4a and 4c positions (Ga and Se respectively) are T2 (or F2). A' or A1 not correspond with this symmetry. There are some publications with the same notation but they are wrong.
Response 1: Thanks for your professional comments and suggestions. Indeed, just as pointed out by the anonymous reviewer, the A' or A1 Raman modes are not corresponding to the cubic Ga2Se3 with the symmetry of F-43 m. It is well known that among A2B3-type (A: Ga, In; B: S, Se, Te) metallic chalcogenides, only Ga2Se3 and In2Te3 show a similar defective zinc-blende structure at ambient conditions. Golding et al. (Golding, T.D.; Boyd, P.R.; Martinka, M.; Amirtharaj, P.M.; Dinan, J.H.; Qadri, S.B.; Zahn, D.R.T.; Whitehouse, C.R. Molecularbeamepitaxial growth and characterization of In2Te3. Journal of Applied Physics, 1989, 65, 1936−1941) observed four prominent Raman peaks for the cubic In2Te3 and assigned them as A, B, C and D modes, accordingly. In the revised manuscript, we reassigned the observed Raman peaks of the cubic Ga2Se3 based on previous Raman scattering investigation for the cubic In2Te3 by assigning the five characteristic Raman peaks in cubic Ga2Se3 as A, B, C, D and E modes, respectively. In this case, one can effectively distinguish all these Raman peaks in the cubic Ga2Se3, as show in the revised Figures 2−4. The context counterparts of the assignments of Raman modes have already been thoroughly modified in the revised manuscript.
Point 2: lines 53-55: Give crystallographic information for the different structures (space group, IT, unit cell parameters).
Response 2: Thanks for your valuable and constructive comments and advisements. According to the anonymous comments and suggestions, we conscientiously read through the previously reported work on the pressure-induced structural phase transition reference for Ga2Se3 and GaSe by synchrotron X-ray diffraction measurement from Takumi et al., again (Takumi, M.; Hirata, A.; Ueda, T.; Koshio, Y.; Nishimura, H.; Nagata, K. Structural phase transitions of Ga2Se3 and GaSe under high pressure. Physica Status Solidi (b), 2001, 223, 423−426). In their studies, a detailed synchrotron X-ray diffraction was chosen to extrapolate the high-pressure phase transition of Ga2Se3 by the new characteristic peak appearance at the pressure point of ~14.0 GPa, and further, the occurrence of phase transition from zinc-blende structure to NaCl-type structure is directly determined by comparing the X-ray diffraction pattern from high-pressure synchrotron experiment and theoretical calculation results. Unfortunately, there is no any related crystallographic information for the different structures (space group, IT, unit cell parameters) to be presented in their in-situ high-pressure synchrotron X-ray diffraction experiment. Of course, according to the anonymous advisements, some indispensable explanation and illustrations were added in the revised manuscript.
Point 3: Line: 78: Give the standard deviations for cell parameters. Including them in the Figure 1.
Response 3: Thanks for your very conscientious comments. According to your valuable advisement, we have already supplemented the standard deviations for cell parameters in the revised Figure 1 and the context counterparts in the revised manuscript.
Point 4: Line 134: In Raman study was used only one hydrostatic environment not several….. what criteria are you using to say that the medium is hydrostatic in Raman studies?
Response 4: Thanks for your crucial and professional comments and suggestions. In the initial design of this present work, we have already considered the criteria of hydrostatic conditions in Raman scattering experiments. As usual, under hydrostatic conditions, the pressures in the center and at the edge of sample chamber are almost equivalent. In order to check the distribution of pressures in the sample chamber, several small rubies were placed in the center and at the edge of the sample chamber. The pressures at different locations were therefore obtained through the wavenumber shift of these ruby fluorescence peaks. It can be seen clearly from Figure 1(a) that under hydrostatic conditions, the pressure in the center of the sample chamber is 13.2 GPa and the pressures at the edge of the sample chamber are 13.2, 13.1, 13.0, 13.0 and 12.9 GPa. The deviatoric stress is too tiny and can be ignored at a given pressure of 13.2 GPa under hydrostatic conditions. However, under non-hydrostatic conditions, the pressure in the center of the sample chamber is 13.5 GPa, and whereas, relatively low pressures of 13.0, 12.5 and 12.0 GPa are obtained at the edge of the sample chamber, as show in Figure 1(b). The magnitude of deviatoric stress is approximately 1.5 GPa at a similar given pressure of 13.5 GPa under non-hydrostatic conditions.
Figure 1. The optical microscope image of the sample chamber. (a) and (b) represent the images under hydrostatic and non-hydrostatic conditions, respectively. In here, PM stands for the pressure medium.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The manuscript presents the results of an experimental study on the behavior of Ga2Se3 under pressure. The effects of non-hydrostatic and hydrostatic environments on the structural phase transition and physical properties were also checked. Binaries of Group 13 and Group 16 elements have been subject of research for many decades. This interest is still quite vivid today. Thus, this work will also contribute to the existing body of knowledge. I hope the experimental findings reported here will attract the attention of computational researchers, because in principle first-principles calculations can provide a much-needed deep insight into the experimental results presented. The structural phase transition can be verified, the lattice dynamics calculations for the phases involved will also be highly valuable. I hesitate to suggest the authors themselves to include the such calculations in this manuscript, because already it is somewhat long. A separate theory work would be better. In any case, the manuscript is of scientific interest and is expected to give rise to more work. The language problems are the main issue. I give a list of some changes below. I recommend acceptance after a minor review.
Literature:
I think the following paper may be relevant, since they mention a new non-centrosymmetric phase of Ga2Se3. Sheng-Ping Guo et al. Angew. Chem. Int. Ed. vol. 58, p. 8087 - 8091.
Language: (selected; authors should also read carefully before resubmission)
Line 33: In recent decades
Line 37, 38: one-third of gallium sites in the crystal structure
Line 45: As far as Ga2Se3 is concerned
Line 66,67: Furthermore, ... discussed in detail.
Line 77: ... software and obtained a = b = c ...
(Remark: Why only two digits for the lattice parameter? How large is the error bar? What is the standard deviation?)
Line 133: performed to investigate
Line 135-137: display the variation ... with pressure in the range of ... and at room .... The corresponding results ..
Line 166: is continuously reduced
Line 210, 211: impedance spectra ... are plotted in Figure 5.
Line 229: drastic increase
Line 237: sample remains relatively
Line 265-268: the sample is a semiconductor. ... which implies metallic behavior. ... temperature-dependent electrical
Line 271-272: typical semiconductor.
Line 285: corresponding
Line 290: closed-packed
Line 294: are cubic Ga2Se3.
Table 1, caption: \omega is referred as the Raman shift, I believe it is the Raman frequency itself. The shift is apparently "d\omega". Also, the caption should state clearly at which pressure the listed "\omega" values were obtained. It should be ambient pressure, I think.
Author Response
Response to Reviewer 2 Comments
Point 1: The manuscript presents the results of an experiment study on the behavior of Ga2Se3 under pressure. The effects of non-hydrostatic and hydrostatic environments on the structural phase transition and physical properties were also checked. Binaries of Group 13 and Group 16 elements have been subject of research for many decades. This interest is still quite vivid today. Thus, this work will also contribute to the existing body of knowledge. I hope the experimental findings reported here will attract the attention of computational researches, because in principle first-principles calculations can provide a much-needed deep insight into the experimental results presented. The structural phase transition can be verified, the lattice dynamics calculations for the phases involved will also be highly valuable. I hesitate to suggest the authors themselves to include the such calculations in this manuscript, because already it is somewhat long. A separate theory work would be better. In any case, the manuscript is of scientific interest and is expected to give rise to more work. The language problems are the main issue. I give a list of some changes below. I recommend acceptance after a minor review.
Response 1: Thanks for your positive and precious comments and advisements.
Point 2: Literature: I think the following paper may be relevant, since they mention a new non-centrosymmetric phase of Ga2Se3. Sheng-Ping Guo et al. Angew. Chem. Int. Ed. Vol. 58, p. 8087-8091.
Response 2: Thanks for your precious comments. According to the anonymous reviewer’s valuable suggestions, we have cited this reference from Guo, S.P. et al. (Guo, S.P.; Cheng, X.Y.; Sun, Z.D.; Chi, Y.; Liu, B.W.; Jiang, X.M.; Li, S.F.; Xue, H.G.; Deng, S.Q.; Duppel, V.; Köhler, J.; Guo, G.C. Large SHG effect and high LIDT observed coexisting in gallium selenide: a simple but perfect case. Angewandte Chemie International Edition, 2019, 58, 8087−8091) in the introduction of the revised manuscript. Indeed, this work is relevant and important to our investigation on the Ga2Se3 because they reported a new non-centrosymmetric phase of Ga2Se3.
Point 3: Language: (selected; authors should also read carefully before resubmission)
Line 33: In recent decades
Response 3: Thanks for your professional and valuable comments. We have replaced the " In recently several decades " to " In recent decades " in the revised manuscript.
Point 4: Line 37, 38: one-third of gallium sites in the crystal structure
Response 4: Thanks for your important suggestion. We have changed from " one-third gallium cations in the crystal lattice " to " one-third of gallium sites in the crystal structure " in the revised manuscript.
Point 5: Line 45: As far as Ga2Se3 is concerned
Response 5: According to your suggestion, we have corrected from " As far as Ga2Se3 " to " As far as Ga2Se3 is concerned " in the revised manuscript.
Point 6: Line 66, 67: Furthermore, …. discussed in detail.
Response 6: Thanks for your valuable comment. We have changed from " And further, …. discussed detailedly " to " Furthermore, …. discussed in detail " in the revised manuscript.
Point 7: Line 77: …… software and obtained a = b =c….
(Remark: why only two digits for the lattice parameter? How large is the error bar? What is the standard deviation?)
Response 7: According to your suggestion, we have corrected from " …… software and some lattice parameters were determined as following: a = b = c = ….. " to " …… software and obtained a = b = c…. " in the revised manuscript. As for the issue of the valid digits, error bar and standard deviation for the lattice parameters, we calculated the lattice parameters of the starting sample again by using Jade 6.5 software and supplemented more valid digits, error bar and standard deviation for the lattice parameters of the starting sample in the revised manuscript.
Point 8: Line 133: performed to investigate
Response 8: Thanks for your valuable and significant comments. We have replaced the " performed to research " to " performed to investigate " in the revised manuscript.
Point 9: Line 135-137: display the variation …. with pressure in the range of …. and at room ….. The corresponding results….
Response 9: Thanks for your valuable comment. We have corrected this issue in the revised manuscript.
Point 10: Line 166: is continuously reduced
Response 10: According to your suggestion, we have corrected the " is continuously decompressed " to " is continuously reduced " in the revised manuscript.
Point 11: Line 210, 211: impedance spectra ….. are plotted in Figure 5.
Response 11: Thanks for your professional and significant comments. We have replaced the " impedance spectroscopy ….. are detailedly plotted in Figure 5 " to " impedance spectra ….. are plotted in Figure 5 " in the revised manuscript.
Point 12: Line 229: drastic increase
Response 12: According to your suggestion, we have changed from " drastic increasement " to " drastic increase " in the revised manuscript.
Point 13: Line 237: sample remains relatively
Response 13: Thanks for your valuable comment. We have corrected this issue in the revised manuscript.
Point 14: Line 265-268: the sample is a semiconductor ….. which implies metallic behavior …. temperature-dependent electrical
Response 14: According to your suggestion, we have changed from " the sample belongs to semiconductor ….. which manifests that the sample is of metallic property…. temperature-variable electrical " to " the sample is a semiconductor ….. which implies metallic behavior …. Temperature-dependent electrical " in the revised manuscript.
Point 15: Line 271-272: typical semiconductor.
Response 15: According to your suggestion, we have changed from " typical semiconducting behaviour " to " typical semiconductor " in the revised manuscript.
Point 16: Line 285: corresponding
Response 16: Thanks for your professional and significant comments. We have corrected " correspondent " to " corresponding " in the revised manuscript.
Point 17: Line 290: closed-packed
Response 17: According to your suggestion, we have changed from " close-packing " to " closed-packed " in the revised manuscript.
Point 18: Line 294: are cubic Ga2Se3
Response 18: Thanks for your professional and precious comments. We have replaced the " are cubic structural Ga2Se3 " to " are cubic Ga2Se3 " in the revised manuscript.
Point 19: Table 1, caption: \omega is referred as the Raman shift, I believe it is the Raman frequency itself. The shift is apparently “d/omega”. Also, the caption should state clearly at which pressure the listed “\omega” values are obtained. It should be ambient pressure, I think.
Response 19: According to your suggestion, we have changed the notation of ω from " Raman shift " to " Raman frequency " and supplemented some detailed explanations for the listed ω values in both Tables 1 and 2 in the revised manuscript.
In sum, as for the issue of English expression skills and writing styles, we have substantially improved and enhanced them in the revised manuscript, accordingly. At this moment, we believe that the revised manuscript makes it possible to be read and understood more easily, and there is a significant and substantial advancement in the writing style and use of English language.
Author Response File: Author Response.pdf
