Synthesis, Structure, and Conductivity of Alluaudite‐Related Phases in the Na₂MoO₄–Cs₂MoO₄–CoMoO₄ System

Abstract

Phase formation study of the Na2MoO4–Cs2MoO4–CoMoO4 system resulted in new cesium‐containing alluaudite‐related phases. The solid solution Na4–2x‐yCsyCo1+x(MoO4)3 (0 ≤ x, y ≤ 0.30), based on the alluaudite‐type Na4–2xCo1+x(MoO4)3, and triple molybdate Na10(Cs4‐xNax)Co5(MoO4)12 (0 ≤ x ≤ 0.30) were found, and their structures were solved. In the structure of Na3.21Cs0.37Co1.21(MoO4)3 (a = 13.0917(8) Å, b = 13.5443(8) Å, c = 7.1217(4) Å, space group C2/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(Cs3.77Na0.23)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 Na25Cs8R5(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+2xFe2‐x(SO4)3 with a 1D conductivity. The measured ionic conductivity of Na4–2xCo1+x(MoO4)3, Na4–2x‐yCsyCo1+x(MoO4)3, and Na10Cs4Co5(MoO4)12 reaches 10–3–10–2 S cm–1 at 500 °C.

New triple molybdate K5ScHf(MoO4)6: Synthesis, properties, structure and phase equilibria in the M2MoO4–Sc2(MoO4)3–Hf(MoO4)2 (M = Li, K) systems

“…Molybdates are well-known and promising as laser materials [1,2], ferroelectrics and ferroelastics [3,4], phosphors [5], ionic conductors [6][7][8][9][10][11], materials for Li(Na)-ion batteries [11,12] etc. Compounds with open 3D frameworks are considered as promising Na, K-or Li-ion conductors or battery materials [13][14][15][16][17][18][19][20]. For example, ionic conductivities 10 −4 −10 −5 S/cm at room temperature were determined for oxides Li 3 M(MoO 4 ) 3 (M = Cr, Fe) [21] with Li atoms in large channels, which is comparable to the conductivity of known lithium ion conductors such as LiAlSiO 4 and LiSbO 3.6 .…”

“…For example, ionic conductivities 10 −4 −10 −5 S/cm at room temperature were determined for oxides Li 3 M(MoO 4 ) 3 (M = Cr, Fe) [21] with Li atoms in large channels, which is comparable to the conductivity of known lithium ion conductors such as LiAlSiO 4 and LiSbO 3.6 . The range of complex Mo(VI) oxide phases has been expanding over the during last decades for account of triple molybdates revealed in the course of exploring ternary salt systems [13,[22][23][24][25][26][27][28][29][30]. A series of CsM 3+ Zr 0.5 (MoO 4 ) 3 compounds with large channels occupied by Cs + ions have a significant electrical conductivity of about 10 −5 S/cm at 800 K with a predominant ionic component above 673 K and average activation energies of 0.3−0.6 eV was measured for M = Al, Sc, In [29].…”

Thallium ionic conductivity of new thallium indium hafnium molybdate ceramics

“…Currently, there is great interest in inorganic compounds (in particular, molybdenum-containing [1]) which exhibit the properties of catalysts [2][3][4], ferroelectric, piezoelectric, photoluminescent [5], laser [6,7], magnetic and have high ionic conductivity [8][9][10][11][12][13][14][15][16][17][18].…”