Impact of Sintering Temperature on the Electrical Properties of La0.9Sr0.1MnO3 Manganite
, Ahlem Guesmi 3, Naoufel Ben Hamadi 3, Lotfi Khezami 3, Essebti Dhahri 4, Kamel Khirouni 5 and Malek Gassoumi 1,*Round 1
Reviewer 1 Report
In the presented article, the authors continue their studies of materials based on lanthanum manganite. This work is devoted to the study of the effect of synthesis temperature on the properties of the material. The research of this material is quite relevant, but the presented article contains a number of flaws that should be corrected before publication.
At first, the lantanum manganite is not very obvious material as catalyst. I believe that the relevance of the article to the journal topic should be explained in the introduction in more details.
Moreover, may you reduce the review of general LSMO properties in the introduction to emphasize the scientific relevance of your paper-specific task? Earlier you researched the composition La0.67Sr0.33MnO3 [61], now you have changed the research object to 0.9-0.1. Why? What do you expect from the composition change?
And for very this composition you have already investigated the transport properties [51]? What your exactly this paper aimed for? I believe you should claim your goals more clearly.
Now by the lines.
line 97. I believed earlier that the oxygen vacancies concentration rise is the cause. Could you provide a reference to the mobility effect?
line 154. The space group was not printed.
line 171. How did you measure the grain size with so fine precision from the micrograph presented? Can you add some explanations about the method?
line 194. Figure 2. You have already investigated the same composition earlier [51] and obtain the different result (monotonic decrease of the resistivity, without any maximum). What is the difference in experiments that explains the difference in results?
lines 247, 249. What are the expressions 2 and 3?
line 314. Figure 5. The same question as above. Similar dependence was obtained in earlier work [51] and it was different. Why? And there are no letters on the figures, which are referenced in the caption.
Comments for author File: 
Comments.pdf
Author Response
In the presented article, the authors continue their studies of materials based on lanthanum manganite. This work is devoted to the study of the effect of synthesis temperature on the properties of the material. The research of this material is quite relevant, but the presented article contains a number of flaws that should be corrected before publication.
At first, the lantanum manganite is not very obvious material as catalyst. I believe that the relevance of the article to the journal topic should be explained in the introduction in more details.
Moreover, may you reduce the review of general LSMO properties in the introduction to emphasize the scientific relevance of your paper-specific task? Earlier you researched the composition La0.67Sr0.33MnO3 [61], now you have changed the research object to 0.9-0.1. Why? What do you expect from the composition change?And for very this composition you have already investigated the transport properties [51]? What your exactly this paper aimed for? I believe you should claim your goals more clearly.
Response
Via the correlations between the magnetic and electrical properties of manganites, the double exchange effect mainly affects the transport properties in manganites. To confirm these hypotheses, we are interested in studying the electrical properties of the LSMO in order to understand the effect of the introduction of a low concentration of Sr. The physical phenomena observed are invested in several applications.
Now by the lines.
line 97. I believed earlier that the oxygen vacancies concentration rise is the cause. Could you provide a reference to the mobility effect?
Response
[1] C. Ang, Z. Yu, Oxygen-vacancy-related low-frequency dielectric relaxation and electrical conduction in Bi: SrTiO3, Physical Review B 62 (2000) 228-236.
[2] W. Hzez, A. Benali, H. Rahmouni, E. Dhahri, K. Khirouni, B. F. O. Costa, Effects of oxygen deficiency on the transport and dielectric properties of NdSrNbO. Journal of Physics and Chemistry of Solids 117 (2018) 1-12.
line 154. The space group was not printed.
Response
The space group has been added ()
line 171. How did you measure the grain size with so fine precision from the micrograph presented? Can you add some explanations about the method?
Response
save TEM images with the SCALE BAR ...if your TEM is good calibrated then the number of pixels forming the BAR gives you a factor F=Angstrom/pixel. Then Just count the number of pixels from one side to the other of your the particle and multiplie by the factor F=Angstrom/pixel that you found from the scale BAR
line 194. Figure 2. You have already investigated the same composition earlier [51] and obtain the different result (monotonic decrease of the resistivity, without any maximum). What is the difference in experiments that explains the difference in results?
Response
In the last work[51]we study the conductivity with the temperature and we have reval that the DC-conductivity analysis reveals that the conduction process is dominated by thermally activated hopping of small. in this work we study the resisitivity.
lines 247, 249. What are the expressions 2 and 3?
Response
Eq(2) 2?fr .τ = 1
Eq(3) τ(T)=τ0 exp(-Ea/(kB T))
I have correct it in the text
line 314. Figure 5. The same question as above. Similar dependence was obtained in earlier work [51] and it was different. Why? And there are no letters on the figures, which are referenced in the caption.
Response
In the last work[51]we study anly the conductivity with the temperature and with frequency but in this work we study the resisitivity.
We have prouve that the decrease in rDC can be related to the fact that as the temperature rises, more charge carriers are released from the trapped centers and participate in the conduction. In perovskite systems (for T > TM-SC), the electrical conductivity is usually generated by hopping conduction processes. The activation of such processes induces the ob-served resistivity decrease.
Thank you very much
Author Response File: Author Response.pdf
Reviewer 2 Report
The authors reported the La0.9Sr0.1MnO3 nanoparticles were prepared using the Citrate–Gel route and sintered at different temperatures (TS = 600 °C, 800 °C, and 1000 °C). I would like to recommend it is publishable after major revision as noted:
- The crystal structure of La0.9Sr0.1MnO3 phases should be added.
- Why did select the temperatures？ How about higher temperature such as 1200 oC？
- The thermal active energy should be given more discussion。
- What is the mechanism of metal-semi-conductor transition ？
- The grain boundaries potential should be discussed in detailed。
Author Response
Thank you very much for your e-mail and valuable suggestion. We appreciate thevaluable comments given by the reviewer, and we hope that our reply listed below is satisfactory.
Reviwer2
The authors reported the La0.9Sr0.1MnO3 nanoparticles were prepared using the Citrate–Gel route and sintered at different temperatures (TS = 600 °C, 800 °C, and 1000 °C). I would like to recommend it is publishable after major revision as noted:
1. The crystal structure of La0.9Sr0.1MnO3 phases should be added.
Response
crystallize in the structure rhombohedral assigned to space group .
2. Why did select the temperatures？ How about higher temperature such as 1200 oC？
Response
The powder is divided into four samples to sinter three of them at 800°C, 1000°C and 1200°C for 12 hours to obtain samples of different particle sizes. Thus, we prepared four samples each is subjected to a different heat treatment (Tr=600°C, 800°C, 1000°C and 1200°C). The annealing step ensures that a material with a well-defined crystalline structure and chemical composition is obtained. Indeed, it improves the homogeneity and the crystallinity of the samples and offers a better connectivity of the grains.
3. The thermal active energy should be given more discussion。
Response
The evolution of AC conductivity with temperature, at some well-chosen frequencies. It is observed that the AC conductivity varies when the temperature increases for each curve. Such behavior proves the thermal activation of the AC conductivity.
It is clearly observed that EAC decreases with the increase in the frequency. This decrease suggests that the hopping mechanism can be considered the dominant conduction process. Indeed, the charge carriers chose the easiest path between the sites, including some jumps that require higher energies for long distances. When increasing the frequency, jumps occur between neighboring sites. Therefore, charge carriers require lower energies for short distances. This result explains the observed reduction in activation energy. In manganites, the activation of the polaron-hopping conduction mechanism varies with the variation of the frequency parameter. Thus, the increase in frequency leads to the creation of new conduction sites and opens a new path for the transport of charges. Therefore, the activation energy is reduced due to the increased jump site density
4. What is the mechanism of metal-semi-conductor transition ？
Response
In the present work and from DC measurements, the metal-semiconductor transition is not well identified. To reliably detect the metal-semiconductor transition, we propose to plot the temperature dependence of the electrical conductivity for different frequencies. In addition, for the measurement procedure, it is believed that it is necessary to reduce the temperature step to obtain more measured points. On the other hand, we know that this transition is linked to the Mn3+/Mn4+ ratio which is itself linked to the Sr concentration. This parameter is also sensitive to the preparation conditions and to the oxygen stoichiometry. To be sure of the presence of this transition, we have plotted the variation of AC conductivity as a function of temperature for certain selected frequencies.
5. The grain boundaries potential should be discussed in detailed。
Response
The electrical behavior of perovskites is known to be dominated by the grain boundary response. In fact, grain boundaries are more resistive than grains. This is due to the non-stoichiometric distribution of oxygen vacancies near grain boundaries [35-37]. Our experimental results support the hypothesis that the ionization of oxygen vacancies creates conduction electrons. This is the process described by the Kröger-Vink notation. These electrons can be trapped by Mn4+ ions. They become conduction electrons under the effect of temperature (by thermal activation) making the grain boundaries more conductive. Grain boundaries contribute to the reduction of electrical resistance due to the high mobility of electrons.
Thank you very much
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Based on the changes made by the authors, I suggested the present manuscript can be accepted.
