Te-Embedded Nanocrystalline PbTe Thick Films: Structure and Thermoelectric Properties Relationship

Round 1

Reviewer 1 Report

This paper reports fabrication as well electrical and thermoelectric properties of PbTe nanocrystalline thick films with Te inclusions. These films were made by electrodeposition in alkaline solution under slightly different applied potential. Next the samples were annealed at 200 deg C for 2 or 10 hours. PbTe  is a candidate for mid-range temperature thermoelectrics (between 150 and 350 deg C).Thereforethe topicis interested. However there are many drawbacks in this manuscrit and they are given below:

1. I think that the volume of the chapter "Introduction" is excessive (and refers to too much references and the article as a whole will look better for reducing the volume of the text in this Chapter.
2. On the other hand, there is a clear difference between the exact description in the text and the presented drawings (photographs).
3. The surface morphology mentioned by the authors (nodular, smoother, rougher) cannot be noticed in Fig. 1. Authors should submit better photos.
4. Also, the X-ray diffraction patterns (Fig. 2) are not readable. The Authors argue that the dominant orientation for PbTe is orientation (111). But the PbTe (222) line is many times stronger than the PbTe (111). In contrast the intensities of the Te (111) and Te (012) lines in the as-deposited compositions are similar. Therefore, it is difficult to speak about preferred orientation (111) for Tellurium.
5. There is no evidence of the increase/decrease in PbTe/Te nanograin sizes during thermal treatment in the study (only words, no figures of strongest peaks).
6. The authors showed that they measured the electrical conductivity as a function of temperature and on this basis they determined the height of the energy barrier (although this is not the temperature range in which PbTe is to be used in thermoelectricity). But it is not clear whether, for example, the mobility of the carrier was measured experimentally or determined theoretically from equation (3).
7. There is no discussion how the electrodeposited PbTe layers with Te doped look from the thermoelectric point of view in comparison with the bulk PbTe crystals.

Due to these comments, I ythink that the paper requires major revision and re-referring.

 

Author Response

We greatly appreciated the reviewer's comment. The author response about the reviewer's comment was attached bellow. 

Author Response File: Author Response.docx

Reviewer 2 Report

This manuscript reports on the synthesis of nanocrystalline PbTe thick films, prepared with excess of Te by electrodeposition (using different rates of deposition) followed by several thermal treatments (0-2h) and caracterized by SEM, EDS and XRD.  The different films obtained were characterized by electrical conductivity, Seebeck coeficient, Hall effect at room temperature, and the Power factor was calculated, as well as the carrier concentration and mobility. The authors tried to correlate the observed transport properties with film parameters like grain size of the two phases present  (PbTe and Te) and volume fraction of PbTe.

 

I do not recommend the acceptance of this manuscript for publication in Coatings, it requires major revisions as minimum:

1-The results and discussion are not presented in straight forward clear way which affects the quality of the work and conclusions that can be drawn from it. There are many graphs in the manuscript with many correlations but the results are incoherent (two Cu contaminated sets of films, that represents half of the films prepared!) and few clear conclusions can be drawn from them.

2-The English is not good and was not carefully written and more than a few times the meaning of the sentences is consequently lost, just a few examples:

Page1 line 35-36

“Thermoelectric (TE) materials, which can directly convert waste heat into usable electric power, has been extensively developed for this issue”

Could be replaced by-

Thermoelectric (TE) materials, which can directly convert waste heat into energy, have been extensively researched for this purpose”

 

Page 6 line 229-231

“In the nanocrystalline PbTe film, the dominant charge transfer mechanism would be significantly affective because its grain size changes as well as the interfaces at two different phases are formed”

Maybe they mean:

“In the nanocrystalline PbTe film, the dominant charge transfer mechanism would be significantly affected because its grain size changes as well as the interfaces as two different phases are formed.

 

Page 8 line 281-283

“The mobility and the electrical conductivity of the as-deposited sample at  0.9 V is larger than expected, which may be caused by varied effective mass according to equation (3) and (4).”

Maybe they mean:

“The mobility and the electrical conductivity of the as-deposited sample at  0.9 V is larger than expected, which may be caused by a lower effective mass according to equations (3) and (4).”

They also do not explain what electrical conductivity they are expecting and why!

 

3- No detail is offered about the method used to measure the Seebeck coefficient or the Hall effect in the thin films

4- Two of the electrodeposited films were contaminated by Cu which introduces at least another phase in the films and therefore introduces another variable that will affect the transport properties in the films and hence the overall coherence of the data and respective conclusions.

5- The introduction of Te nano-inclusions seemed a good idea at first but did not work and the property that could be most positively affected by these nanoengineering changes, the thermal conductivity, was not measured after all.

 

Author Response

We greatly appreciated the reviewer's comment. The author response about the reviewer's comment was attached bellow. 

Author Response File: Author Response.docx

Reviewer 3 Report

                In the manuscript by Tingjun, et.al., the authors report on Te-embedded PbTe thick films grown by electrodeposition methods. By adjusting the Te fraction and growth conditions, the thermoelectric properties can be engineered and improved. The trade-offs between seebeck and electrical conductivity is discussed in terms of the energy barriers due to grain boundaries. Power factor of 183 μw K-2 cm-1 was achieved in the optimized sample.

The work appears to be rigorously done with a suite of characterization such as SEM, XRD, and some basic models to explain the results. However, the work also suffers from serious setbacks that must be addressed before it can be recommended for publication:

1. The discussion on introduction to the topic is clearly lacking and too focused on PbTe. I would suggest the authors to also discuss the general trend and direction of thermoelectrics, and some other promising chalcogenides (GeTe, SnSe) and their relative performance compared to PbTe. The following literatures may be helpful for the authors to consider:

- Journal of the American Chemical Society 142, no. 12 (2020): 5901-5909.

- Materials Today Physics 14 (2020): 100239.

- ACS applied materials & interfaces 12, no. 8 (2020): 9150-9157.

- ACS Applied Materials & Interfaces 12, no. 32 (2020): 36186-36195.

- Journal of Materials Chemistry A 8, no. 36 (2020): 18880-18890.

- ACS Applied Energy Materials 3, no. 3 (2020): 2240-2257.

 

2. The measurement methods of the thin films is not well explained. Traditionally, the thermoelectric properties characterization in thin films is quite tricky, owing to the heat loss to the substrate, which deem the Seebeck measurements inaccurate. The authors can draw inspiration from Scientific reports 10, no. 1 (2020): 1-10 and ACS Applied Materials & Interfaces 12, no. 30 (2020): 33647-33655. to enhance their discussion.

 

3. Equation (2) is only correct if there is no change in scattering mechanisms. How do the authors eliminate the possibility of change in scattering mechanism? Can refer to Adv. Mater. 2021, 33, 2004786 for insights.

 

4.Figure 4 looks confusing, it may help to add fitting or illustration lines to illustrate the trends. Same goes for figure 5a.

 

5. It is worth adding the assumption in the discussion that equation 3 and 4 is only valid for acoustic phonon scattering (the dominant scattering mechanism for most thermoelectrics at room temperature, with some exception)

 

6. The discussion for Figure 6b has to be extended to higher conductivity region, so as not to mislead readers. At even higher conductivity, Seebeck coefficient will decrease, hence the power factor will reach a peak and start decreasing.

 

 

Overall, while the work appears to be carefully done, more work has to be done to correst the setbacks in the introduction and discussion before this paper can be recommended for publication.

 

 

 

 

Author Response

We greatly appreciated the reviewer's comment. The author response about the reviewer's comment was attached bellow. 

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

I do not recommend revised version of the manuscript for publication in Coatings, it continues to require major revisions as minimum:

1-The authors have made minimum changes in the manuscript and did not address the fundamental critic that I made before:

“The results and discussion are not presented in straight forward clear way which affects the quality of the work and conclusions that can be drawn from it. There are many graphs in the manuscript with many correlations but the results are incoherent (two Cu contaminated sets of films, that represents half of the films prepared!) and few clear conclusions can be drawn from them.”

2- Except for the suggestions I made for improving the English (as examples) they did not make any effort to further improve the manuscript.

3- The response for method used to measure the Seebeck coefficient is a “custom-made measurement system”, this could be anything…The method used to measure the Seebeck coefficient in films is certainly published somewhere in the literature and therefore the reference should be provided.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

The authors have made commendable improvements based on the earlier suggestions. The current version of the manuscript is of good quality and can be published as it is.

Author Response

We greatly appreciate the reviewer's comments.