Anisotropies in Elasticity, Sound Velocity, and Minimum Thermal Conductivity of Low Borides VxBy Compounds
Round 1
Reviewer 1 Report
Kindly find my comments in the attached file (review.pdf)
Comments for author File: 
Comments.pdf
Author Response
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Author Response File: Author Response.pdf
Reviewer 2 Report
Yu and coworkers investigate the mechanical properties and the thermal conductivity of different borides from first principles. The anisotropies in elasticity are modeled as a function of boron content, and the dependence of the thermal conductivity on the crystallographic direction is discussed.
The manuscript is potentially interesting for materials scientists dealing with hard metals. However, I cannot judge the soundness of this investigation, as crucial information concerning the simulations is missing. Do the authors employ unit cells or supercells? How large are they? Are the borides ordered crystals or alloys?
In the section III the borides are described as alloys. However, nothing is explained in the methods concerning the simulation of alloys, which are hard to model within the periodic boundary conditions. Alloys must be modeled, e.g., using methods such cluster expansion or special quasirandom structures.
I suggest that the authors add the corresponding information in Sec. III, before any conclusion about the validity of this work is drawn.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
The authors study by means of first principles simulations the thermodynamic stability, elastic properties, sound velocity and minimum thermal conductivity of a series of low boride compounds, which they propose as possible superhard materials. They find that many of these properties are anisotropic, while others such as the sound velocity do not depend too much on the crystallographic direction.
I find the study elaborated, scientifically sound and relevant. The article is well written, although there are some minor grammatical errors and other mistakes, the figures and tables are clear and the physical explanations and descriptions are correct and easy to understand. I think the article might deserve publication, provided the authors address the following comments:
- As commented before, there are some mistakes in the text that should be corrected. For instance, some formulas in the text are missing (see e.g. last two lines of page 2 or the text after formula 8) and some numbers are not properly written (see e.g. the final part of the paragraph of section 2). The format of formula 3 seems to be also completely different from that of other formulas.
- Some observed properties are taken for granted and not properly explained. For instance, why an increase of the Fermi energy implies an increase of the stability? Can this be deduced from the results or is something also observed in other materials?
- There are no many details on how the elastic properties are calculated. While the methods for the determination of the different moduli might be well established and known in the community it would be good to elaborate more on the details of their calculation from the DFT simulations.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Dear editor,
if the investigated compounds are crystalline compounds characterized by an ordered lattice, than the employed methods seem suitable for their investigation.
Considering the answers given to the other referees and the corresponding modifications in the manuscript, I can recommend this work for publication.
