Preparation,Crystal Structure And Magnetoelectric Properties Of Late 3d Transition Metal Oxides

In this paper,several late-3d transition metal oxides and their solid solutions with low-dimensional magnetic ion distribution were synthesized by medium-high temperature solid-phase method,mainly including 12R hexagonal perovskite new compound Ba₄Sn_1.1Mn_2.9O₁₂,Mn/Co doped Fe Bi Pb O₄ and Sr-doped Nd₄Ni₃O_10-δformed solid solution.The phase and structure of the materials were analyzed by means of X-ray diffraction（XRD）,neutron diffraction（ND）,selected area electron diffraction（SAED）and transmission electron microscope（TEM）.The valence of the elements in the materials was analyzed by magnetic susceptibility,brown and altermatt methods.The elements in the materials were analyzed by X-ray energy scattering spectroscopy（EDS）,and the magnetic and conductive properties of these compounds were studied.At the same time,the relationship between crystal structure and magnetoelectric properties is also analyzed.The main research results are as follows:（1）A new hexagonal perovskite compound with chemical formula Ba₄Sn_1.1Mn_2.9O₁₂ was synthesized.The compound has a 12R structure,in which the Ba O₃ layers are in the manner of（cchh）₃ along the c-axis,Sn occupies the octahedral gap between adjacent c-Ba O₃ layers,Mn occupies the octahedral voids between h-Ba O₃layers and between h-Ba O₃ layers and c-Ba O₃ layers.The structure of the material was analyzed by neutron diffraction（nd）,XRD data and selected area electron diffraction（SAED）.It was confirmed that the material has the ordered arrangement of Sn and Mn cations.The study of DC and AC susceptibility shows that the material appears antiferromagnetic long-range order at 6 K.The fitting analysis of magnetic susceptibility data shows that the material exhibits isolated antiferromagnetic cluster behavior between 6 K and 220 K.In the molecular like magnetic cluster state,the chain Mn₃ clusters formed by coplanar connection of Mn O₆ octahedron is dominant,and there are a small number of Mn₂ clusters（due to mixed occupation）.The effective magnetic moment of the Mn₃ cluster is 3.17μ_B,which is close to Mn⁴⁺.At the same time,the spin of the Mn₂ cluster is zero.The formation temperature of magnetic clusters is 220K.Above 220 K,the material shows paramagnetic behavior.The effective magnetic moment of Mn⁴⁺fitted by Curie Weiss paramagnetic formula is 4.2μ_B。The compound has a positive coefficient of thermal expansion and shows semiconductor conductive behavior.The conductivity does not change with the atmosphere,and its conductivity activation energy is 0.61 e V.（2）Fe_1-xMn_xBi Pb O₄ and Fe_1-xCo_xBi Pb O₄,Co-and Mn-doped solid solutions,have quasi one-dimensional chain structure and were synthesized.The solid solution boundaries were determined to be 0≤x≤0.15 and 0≤x≤0.2 by XRD structure refinement.The magnetic susceptibility fitting results show that Fe,Co and Mn in the solid solution formed by Co/Mn doped Fe Bi Pb O₄ are+3 valence ions.XRD refinement results show that when Co³⁺replaces Fe³⁺,the cell parameters of solid solution increase,while Mn³⁺replaces Fe³⁺,the cell parameters decrease.However,the Co³⁺-doped samples have appeared frromagnetic component below T_N,which is related to the 3d⁶ electronic configuration of Co³⁺and the increase of M-M transition metal ion spacing.Both Fe_1-xMn_xBi Pb O₄ and Fe_1-xCo_xBi Pb O₄ solid solutions have semiconducting behavior,and the transport activation energy（Ea）is between 0.2 and0.5 e V.（3）The pure phase of the compound Nd₄Ni₃O_10-δwith n=3 RP phase structure and its Sr-doped Nd_4-xSr_xNi₃O_10-δ（0≤x≤1）solid solution were prepared by various synthetic methods.Room temperature BVS calculation results show that there is obvious charge inhomogeneity between the inner Ni（Ni1/Ni2）and outer Ni（Ni3/Ni4）of Nd_4-xSr_xNi₃O_10-δ,and the average valence of inner Ni is lower than that of outer Ni.The experimental effective magnetic moments in the Nd_4-xSr_xNi₃O_10-δcompounds is almost equal is to the theoretical effective magnetic moment of Nd³⁺,which indicates that the magnetic moment generated by Ni is negligible when T>T_MM（metal-metal phase transition temperature point）,The total atomic magnetic moment of the solid solution compounds are mainly contributed by Nd³⁺.The resistivity versus temperature curve（ρ-T）exhibits paramagnetic metallic behavior over a wide temperature range and resistivity does not change with magnetic field changes.The T_MM of the solid solution Nd_4-xSr_xNi₃O_10-δcompound decreased from 162 K to 150 K with the increase of Sr doping amount.