Abstract
As results of a powder XRD study of sintered samples of the systems Na2MoO4–MMoO4 (M = Co, Cd) quenched in air from 873 K, the literature data on the phase formation and homogeneity ranges of nonstoichiometric double molybdates in these systems were corrected. The compounds are monoclinic alluaudite-type Na4-2xCo1+x(MoO4)3 (0.05 ≤ x ≤ 0.30) and Na4-2xCd1+x(MoO4)3 (0.10 ≤ x ≤ 0.40), orthorhombic lyonsite-type Na2-2yCo2+y(MoO4)3 (0.05 ≤ y ≤ 0.25), and triclinic Na2-2zCo2+z(MoO4)3 (0.10 ≤ z ≤ 0.40) of the Na2Mg5(MoO4)6 type. The temperature of the orthorhombic-to-triclinic phase transition was found to be 943 ± 10 K. Crystal structures of the alluaudite-type double molybdates (space group C2/c, Z = 4) with cobalt, manganese, and cadmium were determined. According to the atomic position occupations, the compositions for the crystals were found as Na3.36Co1.32(MoO4)3 (a = 12.6381(3), b = 13.4888(4), c = 7.1244(2) Å, β = 112.127(1)° R = 0.0207), Na3.13Mn1.43(MoO4)3 (a = 12.7387(3), b = 13.6716(4), c = 7.1904(2) Å, β = 112.404(1)°, R = 0.0166), and Na3.72Cd1.14(MoO4)3 (a = 12.804(3), b = 13.913(3), c = 7.326(2) Å, β = 112.63(1)° R = 0.0158). The crystal chemistry and compositions of the alluaudite-type molybdates and tungstates were considered and mainly one-dimensional character of the sodium-ion transport was shown for them. The measured values of the ionic conductivity of sintered samples of Na3.6M1.2(MoO4)3 (M = Mg, Ni, Zn, Cd) and Na3.6Mg1.2(WO4)3 exceeds 10−3 S cm−1 at 673 K.
Original language | English |
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Pages (from-to) | 121-128 |
Number of pages | 8 |
Journal | Journal of Solid State Chemistry |
Volume | 253 |
DOIs | |
Publication status | Published - 1 Sep 2017 |
Keywords
- Alluaudite
- Cadmium
- Cobalt
- Crystal chemistry
- Crystal structure
- Double molybdates
- Double tungstates
- Homogeneity range
- Ionic conductivity
- Manganese
- Nonstoichiometry
- Sodium
- FUMAROLIC SUBLIMATE
- STRUCTURE CRISTALLINE
- CATHODE MATERIAL
- PHOSPHATE
- PHASE
- PARAGENESIS
- NA
- DESCRIPTIVE MINERALOGY
- IZALCO VOLCANO
- EL-SALVADOR