Improved Oxide Ion Conductivity of Hexagonal Perovskite-Related Oxides Ba₃W_1+xV_1−xO_8.5+x/2

Round 1

Reviewer 1 Report

Manuscript: Inorganics-2413913

The manuscript "Improved Oxide-Ion Conductivity of Hexagonal Perovskite-Related Oxides Ba₃W_1+xV_1-xO_8.5+x/2" submitted to Inorganics by Yugo Kikuchi, Yuta Yasui, James R. Hester and Masatomo Yashima, consists of new information about hexagonal perovskite-related oxides based on Ba₃WVO_8.5. Using different W/V ratios, authors studied the structure and conductivity of the new series of hexagonal perovskite-related oxides Ba₃W_1+xV_1-xO_8.5+x/2 (x = -0.1, -0.05, 0.05, 0.1, 0.25, 0.4, 0.5, 0.6 and 0.75). They observed the large increase in oxygen-ion conductivity for the Ba₃W_1.6V_0.4O_8.8 composition.

In order to understand the main oxide-ion diffusion pathways in these ceramics, the authors used maximum entropy method (MEM) neutron scattering length density (NSLD) analysis of neutron diffraction data at 800 ºC. Structural studies and conductivity measurements have been carried out at a high scientific level in this work. The main question is related to the phase composition of these materials.

1)      It is clear that the optimum composition of Ba3W1.6V0.4O8.8 is two-phase (Figure S1a). Therefore, all Ba₃W_1+xV_1-xO_8.5+x/2 (x = -0.1, -0.05, 0.05, 0.1, 0.25, 0.4, 0.5, 0.6 and 0.75) compositions should be analysed for the second phase BaWO₄. How does the content of the second phase vary throughout the series of samples? Could the high conductivity be due to the composite effect? What is the conductivity of the BaWO₄ phase? It is desirable to provide literature data on this compound.

2)      It is also necessary to determine the exact composition of the nominal composition Ba₃W_1.6V_0.4O_8.8. It should be noted that part of the barium and tungsten was not included in the composition of the solid solution.

3) Please, give the conductivity values at 800 ºC throughout the manuscript. The conductivity at 1000 ºC is of no interest.

 

I suggest a minor revision.

Author Response

Thank you for your kind review and positive comments. We have made responses to your comments. Can you see the attachments?

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Reviewer 2 Report

In this work entitled “Improved Oxide-Ion Conductivity of Hexagonal Perovskite-Related Oxides Ba₃W_1+xV_1-xO_8.5+x/2”, new oxidizes Ba₃W_1+xV_1–xO_8.5+x/2 (x = –0.1, –0.05, 0.05, 0.1, 0.25, 0.4, 0.5, 0.6 and 0.75) have been obtained by the high-temperature solid-state reaction technique. The electrical conductivities of Ba₃W_1+xV_1–xO_8.5+x/2 (x = –0.1, –0.05, 0, 0.05, 0.1, 0.25, 0.4, 0.5, 0.6 and 0.75) were systematically studied. In addition, the DC electrical conductivity σ_DC of Ba₃W_1.6V_0.4O_8.8 was investigated in function of oxygen partial pressure P(O2) at 820 ^oC in dry condition. The bulk conductivity of Ba₃W_1.6V_0.4O_8.8 was found to be 21 times higher than that of mother material Ba₃WVO_8.5 at 500 ^oC. The crystal structure of Ba₃W_1.6V_0.4O_8.8 and Ba₃WVO_8.5 was analyzed using neutron-diffraction data taken in situ at 18 and 800 ^oC. Larger amount of excess W species x makes a larger amount of excess oxygen x/2 in Ba₃W_1+xV_1–xO_8.5+x/2, which leads to the larger amount of oxygen atoms at the O2 and O3 oxygen sites, higher minimum NSLD on the O2–O3 path, and higher conductivity. In general, the work is of interest for the readers of the journal of Inorganics, and the following suggestions could be considered for the authors for a further improvement of the manuscript.

In the introduction part, the choice of Ba₃W_1+xV_1-xO_8.5+x/2 materials can be justified with a small review on the modification of Ba₃M′M′′O_8.5 hexagonal perovskites, and the following work of  Ba₃W_1+xNb_1–xO_8.5+x/2 could be included: (1) Relationship between the Crystal Structure and Electrical Properties of Oxide Ion Conducting Ba₃W_1.2Nb_0.8O_8.6, Inorg. Chem. 2018, 57, 19, 11942–11947, https://doi.org/10.1021/acs.inorgchem.8b01366

The section of “2. Results” and “3. Discussion” could be combined.

 

 

 

Minor editing of English language required

Author Response

Thank you for your kind review.

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Reviewer 3 Report

The present work is reporting on the synthesis and characterization of hexagonal perovskite-related oxides: Ba3W1+xV1-xO8.5+x/2. The study showed an improved oxide-ion conductivity of Ba3W1.6V0.4O8.8 compared to the mother material Ba3WVO8.5 at 500 C. The data are consistent and their discussion is adequate. 

The manuscript needs minor revision taking into consideration the following remarks:

1- The conclusions part is very long and need to be more concise.

2- Some grammar corrections are needed before publication.

 

Some grammar corrections are needed before publication.

Author Response

Thank you for kind review.

Can you see the attachment?

Author Response File: Author Response.docx