物理化学学报 >> 2020, Vol. 36 >> Issue (1): 1907012.doi: 10.3866/PKU.WHXB201907012

所属专题： 庆祝唐有祺院士百岁华诞专刊

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一个各向异性磁稀释杂化钙钛矿系列[CH3NH3][CoxZn1-x(HCOO)3]

陈洒,商冉,王炳武,王哲明*(),高松*()   

  • 收稿日期:2019-07-01 录用日期:2019-09-06 发布日期:2019-09-20
  • 通讯作者: 王哲明,高松 E-mail:zmw@pku.edu.cn;gaosong@pku.edu.cn
  • 基金资助:
    国家自然科学基金(21671008);国家自然科学基金(21621061);国家重点基础研究发展计划(2018YFA0306003)

An Anisotropic Diluted Magnetic Hybrid Perovskite Series of [CH3NH3][CoxZn1-x(HCOO)3]

Sa Chen,Ran Shang,Bingwu Wang,Zheming Wang*(),Song Gao*()   

  • Received:2019-07-01 Accepted:2019-09-06 Published:2019-09-20
  • Contact: Zheming Wang,Song Gao E-mail:zmw@pku.edu.cn;gaosong@pku.edu.cn
  • Supported by:
    the National Natural Science Foundation of China(21671008);the National Natural Science Foundation of China(21621061);the National Key Basic Research Program of China(2018YFA0306003)

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摘要：

作为与传统纯无机钙钛矿材料互补的体系，有机-无机或杂化钙钛矿材料结合了有机和无机成分各自的特性，在相变、临界现象和相关功能性质的研究中展现了众多新的可能性和机会。其中，金属甲酸铵钙钛矿表现优越，且其功能和性质十分依赖于金属离子和铵的特性。本工作借助固体化学中的固溶体策略，研究各向异性磁稀释杂化钙钛矿[CH3NH3][CoxZn1-x(HCOO)3]系列的制备、结构和磁性。该系列的全程固溶体(x = 0–1或摩尔百分比Co% = 0–100%)都可以用溶液化学方法制备获得，并由单晶和粉末X射线衍射确定了固溶体全程同构。它们都属于正交晶系，空间群Pnma，晶胞参数范围为a = 8.3015(2)–8.3207(3) Å，b = 11.6574(4)–11.6811(5) Å，c = 8.1315(3)–8.1427(4) Å，V = 787.89(5)–790.98(7) Å3 (1 Å = 0.1 nm)。钙钛矿结构由金属-甲酸的简单立方阴离子骨架和骨架孔穴中的CH3NH3+阳离子构成，CH3NH3+阳离子和骨架之间形成N―H···O氢键。在这个系列中，固溶体晶体结构的点阵和结构参数几乎没有变化。因此，该系列提供了一个很好的在结构和分子几何参数不变的条件下研究磁稀释效应的分子磁性体系。在逐步稀释的过程中，Co2+离子的磁各向异性和逐渐消失的较大自旋倾斜的贡献，抑制或减少了在低温和低场下的磁化强度，这与各向同性[CH3NH3][MnxZn1-x(HCOO)3]体系在磁稀释时磁化强度增大的行为相反。实验获得的逾渗阈值为(Co%)P = 27(1)% (或xP = 0.27(1))，低于按逾渗理论得到的简单立方格子上的逾渗阈值31%，这也是由于[CH3NH3][CoxZn1-x(HCOO)3]体系磁各向异性的缘故。此外，观察到纯金属Co和Zn成员在约120 K左右发生少见的非公度相变。低温下的非公度性对于磁性质也产生一定的影响。

关键词: 杂化钙钛矿, 金属甲酸铵骨架, 磁稀释, 结构, 磁性

Abstract:

Inorganic-organic or hybrid perovskite materials, which are the complementary counterparts of pure inorganic perovskites, can provide many new opportunities in the researches of phase transitions, critical phenomena, and relevant properties, as they combine the characteristics of inorganic and organic components. Therefore, the hybrid perovskites of ammonium metal formate framework are very promising, and their properties have been found to be strongly dependent on the characteristics of the constituent metal ions and/or ammonium ions. Herein, we used solid solution strategies, borrowed from solid state chemistry, to investigate the anisotropic diluted magnetic hybrid perovskite system of [CH3NH3][CoxZn1-x(HCOO)3], wherein the B-sites are occupied by the mixed metal ions of Co2+ and Zn2+. The solid solution compounds of this series in the range x = 0–1 (or the molar percent Co% = 0–100%) were successfully prepared using conventional solution chemistry methods. The resulting compounds were demonstrated to be iso-structural by using both single-crystal and powder X-ray diffraction analyses. The solid solution crystals belong to the orthorhombic space group Pnma, with the cell parameters being a = 8.3015(2)–8.3207(3) Å, b = 11.6574(4)–11.6811(5) Å, c = 8.1315(3)–8.1427(4) Å, and V = 787.89(5)–790.98(7) Å3. The perovskite structure consists of a simple cubic anionic metal-formate framework and CH3NH3+ cations which are located in the framework cavities, with N―H···O hydrogen bonds formed between the framework and the cation. The members of this series showed negligible changes (< 0.4%) in their respective lattice and structural parameters. Thus, the prepared solid solution compounds constitute good molecule-based examples for the study of magnetic dilution under almost the same structural parameters and molecular geometries. Upon dilution, the magnetization per mole of Co at low temperatures and low fields was suppressed by the magnetic anisotropy of Co2+ and gradual destruction of the large spin canting between coupled Co2+ ions, in contrast to the magnetization enhancement observed in the isotropic diluted system of [CH3NH3][MnxZn1-x(HCOO)3] with the same perovskite structure. The percolation limit was estimated as (Co%)P = 27(1)% (or xP = 0.27(1)) from the magnetic data, which was slightly lower than that predicted by the percolation theory for a simple cubic lattice (31%); this trend was due to the strong magnetic anisotropy of the present system. In addition, rare incommensurate phase transitions were primarily detected below ~120 K for the pure Co and Zn members, which may also affect the magnetic properties of the materials.

Key words: Hybrid perovskite, Ammonium metal formate framework, Magnetic dilution, Structure, Magnetism