Complex Oxide Nanoparticle Synthesis: Where to Begin to Do It Right?

Round 1

Reviewer 1 Report

The manuscript presents a review of the most common methods for the synthesis of ceramic materials and develops a practical methodology for choosing the correct type of metal precursors and solvents for the most typical liquid-phase synthesis methodologies. Then, the developed methodology is put to test by synthesising two complex multi-element oxides. The characterisation employed to study the synthesised oxides is not very thorough, although that is justified given the scope of the manuscript. The manuscript is well written and structured. Therefore, I can recommend its publication after reviewing the following points:

1. In Fig. 1, the authors present “requires little equipment” both as an advantage and as a disadvantage.

2. In page 10, the authors state that they produced a single-phase precipitated oxalate starting with the nitrates, and show its XRD profile as a proof of it being a single-phase. However, the authors also report that all five element selected (Ce, Pr, Sm, Nd and Gd) form oxalates with the same P21/c space group as the single-phase decahydrate oxalate. Therefore, is it possible that the XRD profile corresponded to a physical mixture of single-element oxalates with the same structure and not to the single-phase multi-element oxalate? How can the authors be sure that the oxalate formed is a single-phase one and not a physical mixture of single-element oxalates with the same structure? EDS mapping should be done to the precipitated oxalate prior to the calcination to ensure that it is a single-phase.

3. What is the rationale for the K value of 0.94 in the Scherrer equation? The authors should explain it.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

In the present manuscript, the influence of precursor hydration on the stoichiometric ratio of the final synthesized products is discussed. In addition, the melting point of the precursor and its solubility in different solvents are also studied to assist the selection of precursor materials in liquid phase synthesis. Finally, two kinds of complex materials were synthesized based on the proposed selection method. However, there are some issues need to be resolved before it should be recommended for publication. The following issues should be addressed:

1.       The advantages and disadvantages of solid-phase synthesis and gas-phase synthesis in Figure 1 are in the wrong order.

2.       In the solvent selection section, the manuscript states “When a substance is not soluble in water, it is often soluble in acid at lower pH which can be shifted by using nitric acid or hydrochloric acid.” How should another part of acid insoluble precursors be dissolved to ensure that the chemical reaction process is carried out?

3.       In the synthesis of high-entropy oxide materials, only the solubility of the precursor in the solvent is considered as an influencing factor when liquid-phase synthesis is used to achieve atomic-scale mixing to form a single phase, but the inconsistency of the settling rate of each cation during the dissolution process also leads to changes in the stoichiometric ratio of the product, so is it also necessary to focus on the effect of the solvent on the settling rate of each cation when selecting the solvent?

Author Response

Please see the attachment.

Author Response File: Author Response.pdf