Structure, conductivity and magnetism of orthorhombic and fluorite polymorphs in MoO3-Ln(2)O(3) (Ln = Gd, Dy, Ho) systems

authors	Shlyakhtina, AV; Avdeev, M; Lyskov, NV; Abrantes, JCC; Gomes, E; Denisova, KN; Kolbanev, IV; Chernyak, SA; Volkova, OS; Vasiliev, AN
nationality	International
journal	DALTON TRANSACTIONS
keywords	OXYGEN FUGACITY CONTROL; LN(6-X)MOO(12-DELTA) LN; NONFLOWING ATMOSPHERES; CRYSTAL-STRUCTURE; PROTON; OXIDE; X=0; MO; ND; LA
abstract	Phase-pure orthorhombic compositions at a Ln/Mo ratio similar to 5.2-5.7 (Ln = Gd, Dy, Ho) have been obtained for the first time by prolonged (40-160 h) heat treatment of mechanically activated 5Ln(2)O(3) + 2MoO(3) (Ln = Gd, Dy, Ho) oxide mixtures at 1200 degrees C. Although the starting Ln:Mo ratio was 5:1 (Ln(10)Mo(2)O(21) (Ln = Dy, Ho)), it changed slightly in the final product due to the volatility of molybdenum oxide at 1200 degrees C (40-160 h) (ICP-MS analysis). Brief high-temperature firing (1600 degrees C, 3 h) of 5Ln(2)O(3) + 2MoO(3) (Ln = Gd, Dy, Ho) oxide mixtures leads to the formation of phase-pure fluorites with compositions close to Ln(10)Mo(2)O(21) (Ln = Gd, Dy, Ho). Gd10Mo2O21 molybdate seems to undergo an order-disorder (orthorhombic-fluorite) phase transition in the range of 1200-1600 degrees C. For the first time, using the neutron diffraction method, it was shown that low-temperature phases with a Ln/Mo ratio similar to 5.2-5.7 (Ln = Gd, Dy, Ho) have an orthorhombic structure rather than a tetragonal structure. Proton contribution to the total conductivity of Ln(10)Mo(2)O(21) (Ln = Gd, Dy, Ho) fluorites and gadolinium and dysprosium orthorhombic phases in a wet atmosphere was observed for the first time. In both orthorhombic and fluorite phases, the total conductivity in wet air decreases with decreasing lanthanide ionic radii. In a wide temperature range, the compounds under study exhibit paramagnetic behaviour. However, the orthorhombic phases of Dy and Ho compounds reach the antiferromagnetic state at 2.4 K and 2.6 K, respectively.
publisher	ROYAL SOC CHEMISTRY
issn	1477-9226
isbn	1477-9234
year published	2020
volume	49
issue	9
beginning page	2833
ending page	2842
digital object identifier (doi)	10.1039/c9dt04724g
web of science category	Chemistry, Inorganic & Nuclear
subject category	Chemistry
unique article identifier	WOS:000527534400008