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[Ba3Bi2WO9-comment-160524-R.pdf](https://mdr.nims.go.jp/filesets/c960242a-d8f5-4dce-b4c5-26bddedf2688/download)

## Creator

[Alexei A. Belik](https://orcid.org/0000-0001-9031-2355)

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[In Copyright](http://rightsstatements.org/vocab/InC/1.0/)

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[Does Ba3Bi2WO9 exist?](https://mdr.nims.go.jp/datasets/01370d32-dc91-4b51-9e8c-97409fc8e92f)

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Comments on the paper “Influence of Ba-doping on the structural and physical properties of Sr2−xBaxFeVO6 double perovskites”1  Does Ba3Bi2WO9 exist?  Alexei A. Belik  Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan E-mail: Alexei.Belik@nims.go.jp  Abstract The aim of this commentary is to bring attention of the scientific community to erroneous claims about the existence of a new compound, “Ba3Bi2WO9”, as reported in [Inorg. Chem. Commun. 1530 (2023) 110785]. In this commentary, it is shown that the absence of phase-analysis procedures and incorrect indexing led to erroneous claims. It is demonstrated that a so-called “Ba3Bi2WO9” was a mixture of four phases: BaBiO3−δ (a cubic perovskite with a = 4.3575 Å), Ba3W2O9, BaWO4, and a cubic perovskite with a = 4.225 Å.  Keywords: X-ray diffraction; phase analysis; lattice parameters; errors 2  A recent paper has claimed the synthesis of a new compound with a chemical composition of “Ba3Bi2WO9” [1]. “Ba3Bi2WO9” was prepared using a conventional solid-state method from a stoichiometric mixture of BaCO3, WO3, and Bi2O3 by annealing in air at 1123–1173 K. Reflections on a powder X-ray diffraction pattern of “Ba3Bi2WO9” could be indexed by the authors with lattice parameters of a = 8.4621 Å, b = 6.7358 Å, c = 6.9064 Å, and β = 109.94°. Therefore, the authors of Ref. [1] concluded that a new single-phase compound was prepared, and space group P21 was assigned to “Ba3Bi2WO9”. A powder X-ray diffraction pattern of “Ba3Bi2WO9” contained reflections with very different widths as can be seen from Figure 1a of this commentary, where Figure 1b from Ref. [1] is reproduced. This is a strong indication that the sample in Ref. [1] was not single-phase, and at least two phases were present with different degrees of crystallinity, particle sizes, and/or defects. Our phase analysis could identify three previously known phases, whose reference powder X-ray diffraction patterns are reported in International Center for Diffraction Data (ICDD) database. These phases are BaBiO3−δ with a simple cubic perovskite-type structure (ICDD Powder Diffraction File (PDF) record 86-0618, but with a ≈ 4.3575 Å), Ba3W2O9 (PDF 34-1479), and BaWO4 (PDF 85-0588). There remained a few unidentified reflections, for example, the strongest reflection was at 2θ = 30.0° (with d = 2.976 Å), indexed as (021) on Figure 1a. These reflections did not match with any reference patterns in the ICDD database (of course, under the constraint that just Ba, Bi, W, and O elements should present). On the other hand, these reflections could be explained/indexed by another simple cubic perovskite-type phase with a ≈ 4.225 Å. Therefore, all observed reflections in the sample in Ref. [1] could be explained by the presence of the four phases mentioned above. Note that without the access to the raw sample and raw powder X-ray diffraction data chemical compositions of the proposed phases could only be assigned based on matches with reference powder X-ray diffraction patterns in the ICDD database. As there is no match for the cubic perovskite-type phase with a ≈ 4.225 Å we did not assign a chemical composition to this phase. Note also that the nature of the BaBiO3−δ phase allows wide variations in cation and oxygen stoichiometry, Ba1+xBi1−xO3−δ and Ba1−xBi1+xO3−δ (for example, PDF 85-1806, 48-0936, and 45-0292), depending on synthesis conditions and starting stoichiometry. Nonstoichiometry of the BaBiO3−δ phase and the other perovskite phase (with a ≈ 4.225 Å) could probably explain why the Ba3W2O9 phase was formed in a majority amount in comparison with the BaWO4 phase. In the case of a related “Ba3Bi2MoO9” claim [2], a sample was showed to be mainly a mixture of 2BaBiO3 + BaMoO4 [3]. A small amount of a cubic perovskite phase (with a ≈ 4.20 Å) was also found in “Ba3Bi2MoO9” [3] similar to “Ba3Bi2WO9”. Note that powder X-ray diffraction patterns of the BaBiO3−δ phase and a double perovskite Ba3WO6 phase (PDF 89-5178) are very similar to each other. It is basically impossible to distinguish them by a visual comparison of powder X-ray diffraction data (without a detailed analysis of raw powder X-ray diffraction data) as the fundamental perovskite lattice parameter of Ba3WO6 (ap = 4.31 Å) is close to that of the BaBiO3−δ phase. However, the formation of Ba3WO6 can be ruled out using different information. The preparation of Ba3WO6 requires annealing at 1473–1673 K [4, 5], which is much higher than 3  the annealing temperature used in Ref. [1], and Ba3WO6 is usually formed with a more complicated superstructure [4], for example, with a strong reflection near 26.94° (PDF 33-0182). The powder X-ray diffraction pattern of Ba3WO6 reported in PDF 89-5178 is a calculated pattern based on a simplified structural model, while the original paper [5] (from which PDF 89-5178 was obtained) reported a more complicated superstructure (Figure 1c in Ref. [5]) in agreement with PDF 33-0182. On the other hand, BaBiO3−δ can be prepared at 973–1173 K [6], which is close to the annealing temperature used in Ref. [1]. Moreover, in the case of a related “Ba3Bi2MoO9” claim [2], the presence of BaBiO3−δ was clearly shown [3], and a “Ba3MoO6” compound is not known in comparison with Ba3WO6. Figure 1b shows a resultant powder X-ray diffraction pattern after summation of contributions from all four phases, whose individual contributions are shown on Figure 2. A very good match is observed between the experimental powder X-ray diffraction pattern and the calculated one. The calculated patterns were obtained using the RIETAN-2000 program [7] and Inorganic Crystal Structure Database (ICSD): BaBiO3−δ (code 81316, but with a ≈ 4.3575 Å), Ba3W2O9 (code 100689), and BaWO4 (code 291537). For the fourth, cubic perovskite-type phase, we used the same structural parameters as for BaBiO3−δ, only a lattice parameter was different. The intensity ratios for each phase were adjusted to match with the experimental powder X-ray diffraction pattern. We also used different profile parameters for each phase to reflect different widths on the experimental powder X-ray diffraction pattern of “Ba3Bi2WO9”, where broader reflections belong to BaBiO3−δ. There are also other shortcomings in Ref. [1]. 1) The indexing results reported in Figure 1b of Ref. [1] could not be correct because it is basically impossible to correctly index a sample containing four phases with different symmetries and lattice parameters as a single-phase product even if only strong reflections of four phases are considered (and weaker reflections are omitted). Of course, this statement is true for a reasonable-size cell and acceptable figures of merit for powder pattern indexing (such as, M20 and FN [8]). Such standard figures of merit were not reported in Ref. [1]. In other words, some reflections should show large difference between observed and calculated reflection positions meaning that they remain unindexed, and resulting in unacceptable M20 and FN parameters. 2) Calculated patterns were reported on Figure 1a and Figure 1b of Ref. [1]; however, there were discrepancies between them as some calculated peaks of Figure 1a were missed on Figure 1b. 3) P–E hysteresis loop, reported in Figure 10 of Ref. [1], was only measured up to 1.5 kV/cm, and it just shows leaky dielectric behavior (not a proof of ferroelectric properties). 4) EDX results (Table 1 of Ref. [1]) were reported with very larger errors. In conclusion, a mixture of four phases was investigated in Ref. [1] instead of a new compound, “Ba3Bi2WO9”. The authors in Ref. [1] did not perform any standard phase-analysis procedures, wrongly assumed that a new single-phase compound was obtained, and moved to indexing attempts resulting in erroneous conclusions. Therefore, all other results/measurements in Ref. [1] have little scientific values. In the context of this conclusion, we mention that the claimed “Ba3Bi2MoO9” compound [2] was mainly a mixture of BaBiO3 and BaMoO4 [3] as mentioned before; “Ba3Bi2Fe2O9” [9] was mainly a mixture of two cubic perovskite-type phases [9], which can be called BaFeO3-based and BaBiO3-based; our phase analysis of the claimed “Ca3Bi2MoO9” 4  compound [10] showed that the sample was mainly a mixture of CaMoO4 (PDF 29-0351) and Bi3.11Ca0.89O5.56 (PDF 40-0317) with the presence of some other phases; and “Sr3Bi2MoO9” [11] was experimentally shown to be mainly a mixture of Sr2Bi2O5 and SrMoO4 [12], when prepared at 1073–1123 K.   References [1] S. S. Hota, D. Panda, R. N. P. Choudhary, Studies of structural, dielectric, and electrical properties of polycrystalline barium bismuth tungstate for thermistor application. Inorg. Chem. Commun. 1530 (2023) 110785. doi: 10.1016/j.inoche.2023.110785 [2] D. Panda, S. S. Hota, R. N. P. Choudhary, Development of a novel triple perovskite barium bismuth molybdate material for thermistor-based applications. Mater. Sci. Eng. B 296 (2023) 116616. https://doi.org/10.1016/j.mseb.2023.116616 [3] A. A. Belik, Comments on the paper “Development of a novel triple perovskite barium bismuth molybdate material for thermistor-based applications”. Mater. Sci. Eng. B 303 (2024) 117315. doi: 10.1016/j.mseb.2024.117315 [4] J. Yang, Y. Lv, X. G. Xu, X. P. Song, H. Wei, M. Tian, J. G. Xu, Remarkably high proton conductivity in cubic perovskite-related Ba3WO6. J. Mater. Chem. A 10 (2022) 16697–16703. https://doi.org/10.1039/d2ta04282g [5] E. G. Steward, H. P. Rooksby, Pseudo-cubic alkaline-earth tungstates and molybdates of the R3MX6 type. Acta Cryst. 4 (1951) 503–507. https://doi.org/10.1107/S0365110X51001719 [6] N. Kumar, S. L. Golledge, D. P. Cann, Synthesis and electrical properties of BaBiO3 and high resistivity BaTiO3–BaBiO3 ceramics. J. Adv. Dielect. 6 (2016) 1650032. https://doi.org/10.1142/S2010135X16500326 [7] F. Izumi, T. Ikeda, A Rietveld-analysis program RIETAN-98 and its applications to zeolites. Mater. Sci. Forum 321–324 (2000) 198–205. https://doi.org/10.4028/www.scientific.net/MSF.321-324.198 [8] G. S. Smith, R. L. Snyder, FN: a criterion for rating powder diffraction patterns and evaluating the reliability of powder-pattern indexing. J. Appl. Cryst. 12 (1979) 60–65. https://doi.org/10.1107/S002188987901178X [9] D. Panda, S. S. Hota, S. K. Dash, D. K. Patel, R. N. P. Choudhary, Development of a lead-free colossal dielectric material barium bismuth ferrous oxide for electronic devices. Ceram. Int. 50 (2024) 20098–20107. https://doi.org/10.1016/j.ceramint.2024.03.133 [10] D. Panda, S. S. Hota, R. N. P. Choudhary, Investigation of structural, microstructural, dielectric, and electrical characteristics of a new lead-free compound: Ca3Bi2MoO9. J. https://doi.org/10.4028/www.scientific.net/MSF.321-324.198https://doi.org/10.1016/j.ceramint.2024.03.1335  Mater. Sci.: Mater. Electron. 34 (2023) 1908. https://doi.org/10.1007/s10854-023-11326-5 [11] D. Panda, S. S. Hota, R. N. P. Choudhary, Development of a complex strontium bismuth molybdate material: Microstructural, electrical, and leakage current characteristics for storage and electronic device application. Mater. Res. Bull. 174 (2024) 112727. https://doi.org/10.1016/j.materresbull.2024.112727 [12] A. A. Belik, Does Sr3Bi2MoO9 exist? https://ssrn.com/abstract=4795578 https://doi.org/10.1007/s10854-023-11326-5https://doi.org/10.1007/s10854-023-11326-5https://doi.org/10.1016/j.materresbull.2024.1127276   Figure 1. (a) An experimental X-ray powder diffraction pattern of a “Ba3Bi2WO9” sample from Figure 1b of Ref. [1]. (b) A calculated powder X-ray diffraction pattern of a mixture of BaBiO3−δ (a cubic perovskite with a = 4.3575 Å), Ba3W2O9, BaWO4, and a cubic perovskite with a = 4.225 Å after summation (individual contributions are shown on Figure 2b). The calculated patterns for each phase (intensity ratios) were adjusted to match with the experimental X-ray powder diffraction pattern. Figure 1a is reproduced with the permission from Elsevier.   7    Figure 2. Calculated, individual powder X-ray diffraction patterns of BaBiO3−δ (the black curve and the fourth row (from top) of black tick marks for possible Bragg reflection positions), Ba3W2O9 (the green curve and the third row of green tick marks), BaWO4 (the blue curve and the second row of blue tick marks), and a cubic perovskite with a = 4.225 Å (the red curve and the first row of red tick marks). The calculated patterns (intensity ratios) were adjusted to match with the experimental X-ray powder diffraction pattern.      20 30 40 50 60 70 802θ  (deg): Cu Kα Ba3W2O9 BaBiO3−δ Pm−3m a = 4.3575 Å BaWO4 a cubic perovskite Pm−3m a = 4.225 Å  Abstract References