Shlyakhtina A V, Avdeev M, Lyskov N V, Abrantes J C C, Gomes E, Denisova K N, Kolbanev I V, Chernyak S A, Volkova O S, Vasiliev A N
N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, ul. Kosygina 4, Moscow, 119991 Russia.
Australian Centre for Neutron Scattering, Australian Nuclear Science and Technology Organisation, Kirrawee DC, NSW 2232, Australia.
Dalton Trans. 2020 Mar 3;49(9):2833-2842. doi: 10.1039/c9dt04724g.
Phase-pure orthorhombic compositions at a Ln/Mo ratio ∼ 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 5Ln2O3 + 2MoO3 (Ln = Gd, Dy, Ho) oxide mixtures at 1200 °C. Although the starting Ln : Mo ratio was 5 : 1 (Ln10Mo2O21 (Ln = Dy, Ho)), it changed slightly in the final product due to the volatility of molybdenum oxide at 1200 °C (40-160 h) (ICP-MS analysis). Brief high-temperature firing (1600 °C, 3 h) of 5Ln2O3 + 2MoO3 (Ln = Gd, Dy, Ho) oxide mixtures leads to the formation of phase-pure fluorites with compositions close to Ln10Mo2O21 (Ln = Gd, Dy, Ho). Gd10Mo2O21 molybdate seems to undergo an order-disorder (orthorhombic-fluorite) phase transition in the range of 1200-1600 °C. For the first time, using the neutron diffraction method, it was shown that low-temperature phases with a Ln/Mo ratio ∼ 5.2-5.7 (Ln = Gd, Dy, Ho) have an orthorhombic structure rather than a tetragonal structure. Proton contribution to the total conductivity of Ln10Mo2O21 (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.
通过在1200℃下对机械活化的5Ln₂O₃ + 2MoO₃（Ln = Gd、Dy、Ho）氧化物混合物进行长时间（40 - 160小时）热处理，首次获得了Ln/Mo比约为5.2 - 5.7（Ln = Gd、Dy、Ho）的纯正交相组合物。尽管起始的Ln : Mo比为5 : 1（Ln₁₀Mo₂O₂₁（Ln = Dy、Ho）），但由于1200℃（40 - 160小时）下氧化钼的挥发性，最终产物中的该比例略有变化（电感耦合等离子体质谱分析）。对5Ln₂O₃ + 2MoO₃（Ln = Gd、Dy、Ho）氧化物混合物进行短暂的高温烧制（1600℃，3小时）会导致形成组成接近Ln₁₀Mo₂O₂₁（Ln = Gd、Dy、Ho）的纯相萤石。Gd₁₀Mo₂O₂₁钼酸盐似乎在1200 - 1600℃范围内经历有序 - 无序（正交 - 萤石）相变。首次使用中子衍射方法表明，Ln/Mo比约为5.2 - 5.7（Ln = Gd、Dy、Ho）的低温相具有正交结构而非四方结构。首次观察到质子对Ln₁₀Mo₂O₂₁（Ln = Gd、Dy、Ho）萤石以及钆和镝正交相在潮湿气氛中的总电导率有贡献。在正交相和萤石相中，潮湿空气中的总电导率都随着镧系离子半径的减小而降低。在很宽的温度范围内，所研究的化合物表现出顺磁行为。然而，Dy和Ho化合物的正交相分别在2.4 K和2.6 K时达到反铁磁状态。
