通过超宽139La固体核磁共振波谱研究层状La（OH）2NO3

An Ultrawide-Line 139La Solid-State NMR Investigation of Layered La（OH）2NO3

层状稀土氢氧化物是一类新型的稀土功能材料,本文采用固体核磁共振(SSNMR)方法研究了同时具备离子交换能力和非线性光学特性的层状La(OH)2NO3化合物,探讨了通过四极核CPMG(QCPMG)脉冲序列和变频谱图采集获取超宽^139La SSNMR谱图的方法,并描述了适用于此类实验的滤波方程和谱图重建方法.重建谱图同时包含四极核中心跃迁和卫星跃迁信息,本文使用QUEST软件对超宽^139La NMR谱图进行了模拟,获取的四极耦合常数CQ和非对称因子ηQ均与CASTEP密度泛函理论计算值高度吻合.SSNMR实验结果证实层状La(OH)2NO3化合物属于非中心对称结构(P21),解决了对其结构长期以来存在的争论.

Layered rare earth hydroxides are new classes of functional materials.In this study,a layered La(OH)2 NO3 compound having both ion-exchange capacity and non-linear optical property was studied by solid-state nuclear magnetic resonance(SSNMR)spectroscopy.The quadrupolar Carr-Purcell-Meiboom-Gill sequence(QCPMG)was used to acquire^139La SSNMR sub-spectra with variable offsets,from which the ultrawide-line spectrum was reconstructed by co-addition after applying a filtering function.The ultrawide-line spectrum consisted of both center and satellite transition line shapes,which were also simulated with the QUEST software.The^139La CQ andηQ values measured by SSNMR experiments agreed well with those calculated with the Cambridge Sequential Total Energy Package(CASTEP).The^139La SSNMR results unambiguously indicated that the layered La(OH)2 NO3 compound studied belongs to a non-centro symmetric space group of P21.