钪钇石型β-Mn2V2O7的水热合成、结构表征与反铁磁性

Hydrothermal synthesis,structure characterization and antiferromagnetic properties of thortveitite-type β-Mn_2V_2O_7

用水热法新工艺在温度为200—220℃,pH值为6—9条件下合成出Mn2V2O7粉晶.利用X射线衍射(XRD)、扫描电子显微镜(SEM)、能谱分析(EDS)、透射电子显微镜(TEM)、高分辨透射电镜(HRTEM)和电子衍射(SAED)分析了其物相、形貌及微结构,结果表明:合成产物均为单斜晶系的钪钇石型β-Mn2V2O7;当合成温度为200℃时,pH值为6—7时合成产物的形貌为棒状结构,pH为8—9时的形貌为棒状与花瓣状共存.HRTEM与SAED分析表明了产物的各向异性生长与结晶完整性.利用超导量子干涉仪(SQUID)研究了在1T磁场中,2—300K温度范围内棒状Mn2V2O7粉晶的变温磁化率,结果发现:Mn2V2O7材料在24K左右具有反铁磁—顺磁相变,100K以上的温度下磁化率倒数能很好的符合Curie-Weiss定律,并由此算出顺磁外斯温度θ=-24.6K,居里常数C=9.846emu·K/mol,表明在钪钇石型β-Mn2V2O7材料中存在反铁磁性的相互作用,这种反铁磁性是由Mn2+-O2--Mn2+的超交换作用引起的.

β-Mn2V2OTpowder is successefully prepared at 200--220℃ under pH = 6-9 by a novel hydrothermal synthesis technology. The phase, the morphology and the microstructure of the prepared sample are investigated by XRD, SEM, EDS, TEM, HRTEM and SAED. The results show that 13-Mn2V2O7powder has a thortveitite structure with monoclinic system. The powder synthesized at 200 ℃ under pH = 6-7 has a rod morphology, while that at 200 ℃ under pH = 8-9 has coexistent petal and rod morphologies. HRTEM and SAED measurements indicate that 13-Mn2V2O7 grows anisotropically and has crystalline integrality. Magnetic properties are measured by superconducting quantum interference device （SQUID） in a temperature range of 2-300 K under a magnetic field of IT. The magnetic measurement results indicate that 13-Mn2V2O7undergoes a transition from antiferromagnetic to paramagnetic with a N6el temperature of 24 K. Above 100K, the inverse susceptibility is fitted well to the Curie-Weiss law and paramagnetic Weiss temperature 0 = - 24.6 K, and the Curie constant C = 9. 846 K emu mol-f, u.^-1can be caculated, which means that there exists an obvious antiferromagnetic interaction in thortveitite-type 13 - Mn2V2O7, the antiferromagnetic behavior is caused by the superchange of Mn2＋ - 02- - Mn2＋ .