An Anisotropic Diluted Magnetic Hybrid Perovskite Series of [CH₃NH₃][Co<i>_x</i>Zn_1-<i>x</i>(HCOO)₃]

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 Co 2+ and Zn 2+ . 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) Å 3 . 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 Co 2+ and gradual destruction of the large spin canting between coupled Co 2+ 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.

The materials of ammonium metal formate framework: structures, phase transitions and functionalities

“…该系列的Co、Cu成员在早期已被报道 [59,60] , 制结构, 调制波矢q≈0.13×c* [35,62] . 最近, Co成员的低温 调制或非公度结构及其复杂的相变被报道(图9) [65,66] , [34] (网络版彩图) 表 2 部分钙钛矿AMFF的结构相变和磁相变特征 赵银花等: 金属甲酸铵材料: 结构、相变、性质和功能 67] , NH 2 NH 3 + 适中的大小导致了该系统的多 形性 [38,68,69] .…”

“…最近, Co成员的低温 调制或非公度结构及其复杂的相变被报道(图9) [65,66] , [34] (网络版彩图) 表 2 部分钙钛矿AMFF的结构相变和磁相变特征 赵银花等: 金属甲酸铵材料: 结构、相变、性质和功能 67] , NH 2 NH 3 + 适中的大小导致了该系统的多 形性 [38,68,69] . 相II的化合物都发生结构相变, [61,62] (网络版彩图) 图 10 [NH 2 NH 3 ][Mn(HCOO) 3 ]相II的结构相变机制(a)、变温介电谱(b)和各向异性热膨胀(c) [34] (网络版彩图) . Mn、Co、Ni成员的合成和磁性由我 们首先报道, 在低温下它们是弱铁磁体 [18,19] .…”

Series of Cage-Like Double Perovskite-Type Hybrid Perovskites with Reversible Structural Phase Transition and Switchable Dielectric Constant Property

“…Hybrid organic-inorganic perovskites (HOIPs) cover a diverse range of compositions and have achieved novel properties, such as dielectric transitions, ferroelectricities, and antiferroelectricities. − With the development of hybrid materials, the ABX 3 -type HOIPs, which mimic the all-inorganic ABO 3 structure, have obtained much attention in physics and materials science . In ABX 3 -type HOIPs, the A metal ion is occupied by a midsized molecular cation, while the O ion is replaced by a monatomic and/or polyatomic anionic bridging ligand to form a normal cage-like perovskite structure. − The organic components introduce additional functionalities and structural flexibility, and accordingly many members of the family show attractive characteristics, such as the excellent photovoltaic performance in the star compound (CH 3 NH 3 )­PbI 3 . − …”