Synthesis, Structure, and Conductivity of Alluaudite‐Related Phases in the Na2MoO4–Cs2MoO4–CoMoO4 System. Issue 2 (27th December 2018)

• Record Type: Journal Article
• Authors: Yudin, Vasiliy N.; Zolotova, Evgeniya S.; Solodovnikov, Sergey F.; Solodovnikova, Zoya A.; Korolkov, Iliya V.; Stefanovich, Sergey Yu.; Kuchumov, Boris M.
• Is Part Of: European journal of inorganic chemistry. Issue 2(2019)
• Page Start: 277
• Page End: 286
• Publication Date: 2018-12-27
• Subjects: Molybdenum -- Sodium -- Phase diagrams -- Solid‐state structures -- Conducting materials; Chemistry, Inorganic -- Periodicals; Organometallic chemistry -- Periodicals; Bioinorganic chemistry -- Periodicals; Solid state chemistry -- Periodicals; 546
• DOI: 10.1002/ejic.201801307
• Languages: English
• ISSNs: 1434-1948

Abstract

Abstract : Phase formation study of the Na2 MoO4 –Cs2 MoO4 –CoMoO4 system resulted in new cesium‐containing alluaudite‐related phases. The solid solution Na4–2 x ‐ y Cs y Co1+ x (MoO4 )3 (0 ≤ x, y ≤ 0.30), based on the alluaudite‐type Na4–2 x Co1+ x (MoO4 )3, and triple molybdate Na10 (Cs4‐ x Na x )Co5 (MoO4 )12 (0 ≤ x ≤ 0.30) were found, and their structures were solved. In the structure of Na3.21 Cs0.37 Co1.21 (MoO4 )3 ( a = 13.0917(8) Å, b = 13.5443(8) Å, c = 7.1217(4) Å, space group C 2/ c, β = 112.331(2), Z = 4), the cesium ions partially substitute the Na + in the channels running along the c ‐axis. The structure of Na10 (Cs3.77 Na0.23 )Co5 (MoO4 )12 ( a = 13.6572(3) Å, b = 11.5063(3) Å, c = 27.9898(5) Å, space group Pbca, Z = 4) was proved to be the aristotype for the pseudo orthorhombic Na25 Cs8 R 5 (MoO4 )24 ( R = Fe, Sc, In). The compounds contain alluaudite‐like layers of MoO4 tetrahedra and pairs of edge‐shared (Co, Na)O6 or ( R, Na)O6 and NaO6 octahedra, which are connected by bridging MoO4 tetrahedra to form 3D frameworks differing from the alluaudite type. The frameworks contain channels along the c ‐axis filled by Cs + and Na + ions. Bond valence sum (BVS) maps show that the alluaudite‐related molybdates can have a 2D sodium‐ion conductivity at elevated temperatures in contrast to the alluaudite‐type cathode material Na2+2 x Fe2‐ x (SO4 )3 with a 1D conductivity. The measured ionic conductivity of Na4–2 x Co1+ x (MoO4 )3, Na4–2 x ‐ y Cs y Co1+ x (MoO4 )3, and Na10 Cs4 Co5 (MoO4 )12 reaches 10 –3 –10 –2 S cm –1 at 500 °C. Abstract : The phase relations, structures, ionic conductivity, and Na‐ion migration pathways for alluaudite‐related Na4–2 x ‐ y Cs y Co1+ x (MoO4 )3 and Na10 (Cs4‐ x Na x )Co5 (MoO4 )12 (new type) were determined. Introducing Cs + blocks 1D Na‐conductivity in the former phase, but it leads to possible 2D conductivity for the latter and the highest Na + mobility among known alluaudite‐related molybdates at elevated temperatures.