Fjellvåg Øystein S, Gonano Bruno, Bernal Fabian L M, Amedi Salah B, Lyu Jike, Pomjakushin Vladimir, Medarde Marisa, Chernyshov Dmitry, Marshall Kenneth, Valldor Martin, Fjellvåg Helmer, Hauback Bjørn C
Department for Hydrogen Technology, Institute for Energy Technology, P.O. Box 40, Kjeller NO-2027, Norway.
Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute, Villigen-PSI CH-5232, Switzerland.
Inorg Chem. 2024 Jun 10;63(23):10594-10602. doi: 10.1021/acs.inorgchem.4c00931. Epub 2024 May 24.
Large quantities of high-purity NHCrF have been synthesized using a wet-chemical method, and its structural chemistry and magnetic properties are investigated in detail for the first time. NHCrF is a tetragonal fluoroperovskite that displays an ordering of the ammonium (NH) groups at room temperature and C-type orbital ordering. The ammonium groups order and display distinct signs of hydrogen bonds to nearby fluoride anions by buckling the Cr-F-Cr angle away from 180°. The ammonium ordering remains up to 405 K, much higher than in other ammonium fluoroperovskites, indicating a correlation between the flexibility of the Jahn-Teller ion, the hydrogen bond formation, and the ammonium ordering. At 405 K, an order-to-disorder transition occurs, where the ammonium groups disorder, corresponding to a transition to higher symmetry. This is accompanied by a contraction of the unit cell from breaking hydrogen bonds, similar to the phenomenon observed in water ice melting. The compound orders antiferromagnetically with a Neél temperature of 60 K, an effective paramagnetic moment of 4.3 μ, and a Weiss temperature of -33 K. An A-type antiferromagnetic structure is identified by neutron diffraction, with an ordered moment of 3.72(2) μ.
采用湿化学方法合成了大量高纯度的NHCrF，并首次对其结构化学和磁性进行了详细研究。NHCrF是一种四方氟钙钛矿，在室温下显示铵（NH）基团有序排列以及C型轨道有序排列。铵基团通过使Cr-F-Cr角偏离180°而有序排列，并显示出与附近氟阴离子形成氢键的明显迹象。铵的有序排列在高达405 K时仍保持，远高于其他铵氟钙钛矿，这表明 Jahn-Teller 离子的柔韧性、氢键形成和铵的有序排列之间存在关联。在405 K时，发生从有序到无序的转变，此时铵基团无序排列，对应于向更高对称性的转变。这伴随着由于氢键断裂导致的晶胞收缩，类似于在水冰融化中观察到的现象。该化合物以60 K的尼尔温度、4.3 μ的有效顺磁矩和-33 K的魏斯温度反铁磁有序排列。通过中子衍射确定了一种A型反铁磁结构，其有序磁矩为3.72(2) μ。
