State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, PR China.
Dalton Trans. 2012 Oct 7;41(37):11507-18. doi: 10.1039/c2dt31462b. Epub 2012 Aug 17.
The n = 1 Ruddlesden-Popper (RP) phases LaSrM(0.5)Ru(0.5)O(4±δ) (M = Co, Ni and Zn) have been prepared by solid state reactions and structurally characterized by powder X-ray and electron diffraction. All the samples adopt the tetragonal I4/mmm space group with random M and Ru cation occupation on the B-sites. The potential causes of no cation ordering are discussed. A combined analysis of the tolerance factors, the distortion of the octahedral coordination of M and Ru cations and the magnetic interactions between M and Ru cations provide a better understanding for forming a phase with 3D cation ordering on the B-sites in the n = 1 RP phases. The investigation of XPS spectra suggests that the transition element species exist as mixed ion pairs, Ru((4-δ)+)-Ru(4+)↔ Co(2+)-Co(3+) in LaSrCo(0.5)Ru(0.5)O(4), and Ru(4+)-Ru((4+δ)+)↔ Ni(+)-Ni(2+) in LaSrNi(0.5)Ru(0.5)O(4), which is consistent with cation disorder over the B sites. LaSrCo(0.5)Ru(0.5)O(4) shows a weakly ferromagnetic behaviour below 50 K; LaSrNi(0.5)Ru(0.5)O(4) is evidenced by the presence of long-range magnetic ordering at a Néel temperature of 125 K, and LaSrZn(0.5)Ru(0.5)O(4) exhibits a paramagnetic behaviour down to 5 K. Due to atomic disorder, Ru4d, O2p covalent coupling is weakened, strengthening the intraatomic spin-spin coupling among the π* electrons. Charge transfer between Ru and Co or Ru and Ni, as well as the increasing overlap of both nearest-neighbour and next-nearest-neighbour Ru 4d electrons due to atomic disorder, favour the formation of ferromagnetic interactions. Although antiferromagnetism is dominant, particularly in LaSrNi(0.5)Ru(0.5)O(4), ferromagnetic interactions are stronger in the title compounds than in the related La(2)MRuO(6) (M = Co, Ni) double perovskites where the B-site cations are ordered.
n=1 的 Ruddlesden-Popper（RP）相 LaSrM(0.5)Ru(0.5)O(4±δ)（M=Co、Ni 和 Zn）通过固相反应制备，并通过粉末 X 射线和电子衍射进行结构表征。所有样品均采用四方 I4/mmm 空间群，B 位上的 M 和 Ru 阳离子随机占据。讨论了没有阳离子有序的潜在原因。对容忍因子、M 和 Ru 阳离子的八面体配位畸变以及 M 和 Ru 阳离子之间的磁相互作用的综合分析，为在 n=1 RP 相中形成具有 3D 阳离子有序的 B 位相提供了更好的理解。XPS 光谱的研究表明，过渡金属物种以混合离子对的形式存在，LaSrCo(0.5)Ru(0.5)O(4)中为 Ru((4-δ)+)-Ru(4+)↔Co(2+)-Co(3+)，LaSrNi(0.5)Ru(0.5)O(4)中为 Ru(4+)-Ru((4+δ)+)↔Ni(+)-Ni(2+)，这与 B 位上的阳离子无序一致。LaSrCo(0.5)Ru(0.5)O(4)在 50 K 以下表现出弱铁磁性；LaSrNi(0.5)Ru(0.5)O(4)在 125 K 的奈尔温度下表现出长程磁有序，而 LaSrZn(0.5)Ru(0.5)O(4)在 5 K 以下表现出顺磁行为。由于原子无序，Ru4d、O2p 共价耦合减弱，增强了π*电子之间的原子内自旋-自旋耦合。Ru 与 Co 或 Ru 与 Ni 之间的电荷转移，以及由于原子无序导致的最近邻和次近邻 Ru 4d 电子的重叠增加，有利于形成铁磁相互作用。尽管反铁磁相互作用占主导地位，特别是在 LaSrNi(0.5)Ru(0.5)O(4)中，但标题化合物中的铁磁相互作用强于相关的 La(2)MRuO(6)（M=Co、Ni）双钙钛矿，其中 B 位阳离子有序。
