Attaining Low Lattice Thermal Conductivity in Half-Heusler Sublattice Solid Solutions: Which Substitution Site Is Most Effective?
Round 1
Reviewer 1 Report
In this manuscript, the authors report the lattice term of the thermal conductivity of half-Heusler compounds, some of which can exhibit high thermoelectric performance. The authors calculated the thermal conductivity originating from the three-phonon scattering, the mass-disorder scattering, and grain-boundary scattering. The authors found that several compounds possessing large intrinsic lattice thermal conductivity could be promising thermoelectric materials due to small lattice thermal conductivity obtained within the mass-disorder and grain-boundary phonon scattering mechanisms. The authors discuss the materials dependence of the thermal conductivity, and it is found that elemental substitution at the optimal site can strongly reduce the thermal conductivity, e.g. TiNiPb exhibits the intrinsic thermal conductivity of 22.2 W/Km but the mass-disorder term of 4.6 W/Km. This large reduction can be understood by the atomic mass at the optimal site and the magnitude of the mass-variance parameter. The authors conclude that the presence of heavy atoms is a typical attractive feature of thermoelectric materials.
Important aspects of this manuscript are that the authors theoretically revealed the effect of the elemental substitution on the lattice thermal conductivity and found a tendency to realize high thermoelectric performance. The guideline obtained in this study is generally used for exploring thermoelectric materials in not only in half-Heusler but also in other systems. As the authors discussed in the manuscript, other scattering mechanisms, which may further decrease the thermal conductivity, are not included in this study, but I think that this manuscript provides relevant information to the community working in this field.
Based on the above, the manuscript is suitable for publication in Electronic Materials after minor revision. I have following comments about minor revision.
(1) In Figure 2, it is hard to see the intrinsic term of the thermal conductivity of LaRhTe and LaPtSb at 700K. The width of the brown bars should be wider than the present width.
(2) The substitution concentration used in this study should be described not only in Section 4.1 but also in Section 2.3.
Author Response
Reviewer #1: In this manuscript, the authors report the lattice term of the thermal conductivity of half-Heusler compounds, some of which can exhibit high thermoelectric performance. The authors calculated the thermal conductivity originating from the three-phonon scattering, the mass-disorder scattering, and grain-boundary scattering. The authors found that several compounds possessing large intrinsic lattice thermal conductivity could be promising thermoelectric materials due to small lattice thermal conductivity obtained within the mass-disorder and grain-boundary phonon scattering mechanisms. The authors discuss the materials dependence of the thermal conductivity, and it is found that elemental substitution at the optimal site can strongly reduce the thermal conductivity, e.g. TiNiPb exhibits the intrinsic thermal conductivity of 22.2 W/Km but the mass-disorder term of 4.6 W/Km. This large reduction can be understood by the atomic mass at the optimal site and the magnitude of the mass-variance parameter. The authors conclude that the presence of heavy atoms is a typical attractive feature of thermoelectric materials.
Important aspects of this manuscript are that the authors theoretically revealed the effect of the elemental substitution on the lattice thermal conductivity and found a tendency to realize high thermoelectric performance. The guideline obtained in this study is generally used for exploring thermoelectric materials in not only in half-Heusler but also in other systems. As the authors discussed in the manuscript, other scattering mechanisms, which may further decrease the thermal conductivity, are not included in this study, but I think that this manuscript provides relevant information to the community working in this field.
Based on the above, the manuscript is suitable for publication in Electronic Materials after minor revision. I have following comments about minor revision:
We thank the reviewer for the positive comments, indicating that our manuscript can provide relevant information to the research community.
(1) In Figure 2, it is hard to see the intrinsic term of the thermal conductivity of LaRhTe and LaPtSb at 700K. The width of the brown bars should be wider than the present width.
We thank the reviewer for pointing out this issue on visibility. The background bars indicating the intrinsic lattice thermal conductivity in Fig. 2 are widened in the revised version.
(2) The substitution concentration used in this study should be described not only in Section 4.1 but also in Section 2.3.
We thank the reviewer for this helpful comment. We describe the substitution concentration in Sec. 2.2, “Alloying Scheme” in the revised manuscript.
Again, we thank the reviewer for providing feedback and comments which highly improve the quality of our manuscript.
Reviewer 2 Report
The paper by Trans et al. was the first to provide theoretical evidence to support the lattice contribution to thermal conductivity. Overall, the publication gives an outstanding theoretical study on half heusler compounds with strong thermoelectric performance. However, many details have to be elucidated in order to validate the theory used to explain all transport features. I have included some examples of questions below:
1) According to authors claim the sublattice disorder is experimentally challenging. However, in recent year there is tremendous experimental improvement to form single single phase half heusler compounds (Nature Materials volume 19, pages849–854 (2020; Nat Commun 5, 3525 (2014)). In reviewer opinion authors need to discussion recent advances Half-Heusler compounds.
2) Recent material science improvements successfully govern the substitution of the heaviest atom on the host site to enhance the different material preparties as indicated in Sci Rep 9, 18883. (2019); Adv. Mater. Interfaces, 2: 1500344. Authors may need to discuss those work in revised manuscript.
Author Response
Reviewer #2: The paper by Trans et al. was the first to provide theoretical evidence to support the lattice contribution to thermal conductivity. Overall, the publication gives an outstanding theoretical study on half heusler compounds with strong thermoelectric performance. However, many details have to be elucidated in order to validate the theory used to explain all transport features. I have included some examples of questions below:
We are very thankful to the reviewer for the positive remarks made regarding our theoretical study of the lattice thermal conductivity.
1) According to authors claim the sublattice disorder is experimentally challenging. However, in recent year there is tremendous experimental improvement to form single single phase half heusler compounds (Nature Materials volume 19, pages849–854 (2020; Nat Commun 5, 3525 (2014)). In reviewer opinion authors need to discussion recent advances Half-Heusler compounds.
We thank the reviewer for making us aware of the great progress being made on synthesis of half-Heusler alloys and for recommending previous works to include in the revised manuscript.
In the Sec. 1 Introduction, we have in the revised manuscript discussed the outstanding progress which has been made in the synthesis of alloys, realizing single-phase half-Heusler alloys. We have also included additional references.
2) Recent material science improvements successfully govern the substitution of the heaviest atom on the host site to enhance the different material preparties as indicated in Sci Rep 9, 18883. (2019); Adv. Mater. Interfaces, 2: 1500344. Authors may need to discuss those work in revised manuscript.
We highly appreciate this remark made by the reviewer, suggesting a discussion on how alloying can serve many purposes in terms of tuning material properties. We also thank the reviewer for suggesting excellent literature to include in our revised manuscript.
In the Sec. 1 Introduction, of the revised manuscript, we discuss how alloying can be used to modify material properties other than the lattice thermal conductivity, such as optoelectronic and electrolytic properties. We have included references suggested by the reviewer as well as additional literature.
The following are points where we did not achieve full score on our submission, followed by comments regarding how we assessed the necessary changes.
Moderate English changes required.
We wholeheartedly agree that both language and precision of the text was lacking, and thank the reviewer for pointing this out. The entire paper has been carefully revised. We thoroughly addressed weak parts of our text and found several ambiguities that are corrected in the revised manuscript.
Does the introduction provide sufficient background and include all relevant references?
The introduction in the revised manuscript has been extended and paragraphs 2, 3 and 4 have been rewritten. We have included relevant references on half-Heusler synthesis, isovalent substitutions, and alloying in general. We also added references for previous research in which record breaking thermoelectric efficiency was achieved. We thank the reviewer for sharing additional relevant references, which are included in the revised manuscript.
Is the research design appropriate?
We have in the revised manuscript added a more detailed explanation on the interpolation method used as well as theory, supporting the design choices.
Are the conclusions supported by the results?
Thanks to the reviewer, we could further explain why certain compounds have a large drop in lattice thermal conductivity. We did this by including a discussion in Sec. 4.2 on how large mass differences in certain compounds could lead to a smaller three-phonon scattering volume, as additional scattering mechanisms could have a strong effect in such compounds.
When revising the manuscript, we also focused on clarity in the presentation of the results. This was done with the intention of making an easier transition from the result sections to the discussion and conclusions.
Once more, we are very grateful for the useful comments and feedback from the reviewer, that we believe have added great value to the paper.
