Oró-Solé Judith, Frontera Carlos, Guarín Jhonatan R, Gàzquez Jaume, Mundet Bernat, Ritter Clemens, Fontcuberta Josep, Fuertes Amparo
Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus UAB, 08193 Bellaterra, Spain.
Institut Català de Nanociència i Nanotecnologia (ICN2), Campus UAB, 08193 Bellaterra, Barcelona, Spain.
Chem Mater. 2024 Oct 9;36(20):10267-10275. doi: 10.1021/acs.chemmater.4c02114. eCollection 2024 Oct 22.
The new double perovskite oxynitride BaMnWON has been obtained by topochemical ammonolysis at 700 °C of B-site ordered BaMnWO using a high NH flow rate of 600 cm/min. The relatively low synthesis temperature hinders the cation mobility, allowing the order of Mn and W cations of the precursor oxide to be unperturbed in the oxynitride. Synchrotron X-ray diffraction, electron diffraction, and neutron diffraction indicate that BaMnWON crystallizes in the 3̅ space group with a larger parameter of 8.2434(5) Å compared to BaMnWO [8.20337(1) Å]. Magnetic susceptibility measurements show that BaMnWON orders antiferromagnetically below = 3.8 K, and the observed Curie-Weiss temperature θ = -70(3) K indicates a frustrated Mn lattice with frustration parameter = |θ|/ ≈ 18, which is significantly larger than for the oxide ( ≈ 7.2). The substitution of oxide by the nitride anion induces the oxidation of Mn to Mn and a subsequent decrease of the paramagnetic effective moment from 6.28 to 5.16 μ/f.u. The observation in the oxynitride of a frustration parameter which is larger than twice that of the oxide precursor is rationalized as caused by the relative enhancement of the nearest neighbors' magnetic interactions ( ) Mn-(O/N)-(O/N)-Mn at 90°, compared to next-nearest neighbors' interactions at 180° ( ) Mn-(O/N)-W-(O/N)-Mn, due to the smaller electronegativity of nitrogen compared to oxygen that increases the covalency of bonding. These results expand the chemical and structural diversity of complex transition metal oxynitrides and provide a new route to tailor spin frustration in transition metal double perovskites.
新型双钙钛矿氮氧化物BaMnWON是通过在700℃下对B位有序的BaMnWO进行拓扑化学氨解反应制得的，氨气流速高达600 cm³/min。相对较低的合成温度阻碍了阳离子的迁移，使得前驱体氧化物中Mn和W阳离子的有序排列在氮氧化物中得以保持。同步辐射X射线衍射、电子衍射和中子衍射表明，BaMnWON属于3̅空间群，其晶格参数为8.2434(5) Å，比BaMnWO [8.20337(1) Å]更大。磁化率测量结果显示，BaMnWON在低于3.8 K时呈现反铁磁有序，观测到的居里 - 外斯温度θ = -70(3) K表明其Mn晶格存在自旋阻挫，阻挫参数 = |θ|/ ≈ 18，显著大于氧化物（≈ 7.2）。氮阴离子取代氧化物导致Mn氧化为Mn³⁺，顺磁有效磁矩从6.28 μB/f.u.降至5.16 μB/f.u.。氮氧化物中阻挫参数大于氧化物前驱体两倍的现象可以解释为，与180°的次近邻相互作用（ ）Mn-(O/N)-W-(O/N)-Mn相比，90°的最近邻磁相互作用（ ）Mn-(O/N)-(O/N)-Mn因氮的电负性小于氧而增强，从而增加了键的共价性。这些结果拓展了复杂过渡金属氮氧化物的化学和结构多样性，并为调控过渡金属双钙钛矿中的自旋阻挫提供了一条新途径。
