Brinkmann Christian, Faske Sandra, Vogel Michael, Nilges Tom, Heuer Andreas, Eckert Hellmut
HASYLAB at DESY, Notkestr. 85, 22607 Hamburg, Germany.
Phys Chem Chem Phys. 2006 Jan 21;8(3):369-78. doi: 10.1039/b512236h. Epub 2005 Oct 31.
The relation between structure and ion dynamics in the three polymorphs of Ag(5)Te(2)Cl has been investigated using (109)Ag, (125)Te, and (35)Cl NMR spectroscopies. Specifically, the influence of the structural phase transitions observed near 240 K (P2(1)/c<-->P2(1)/n) and near 332 K (P2(1)/n<-->I4/mcm) upon silver ion mobilities has been studied by temperature dependent (109)Ag NMR lineshapes and spin-lattice relaxation times. While the superionic high temperature phase alpha-Ag(5)Te(2)Cl is characterized by a molten cationic sublattice, fast ion dynamics in the medium-temperature phase beta-Ag(5)Te(2)Cl occurs in spatially restricted regions comprising all the crystallographically distinct silver sites. Temperature dependent magic-angle-spinning linewidths yield an activation energy of 0.38 eV, consistent with 0.44 eV measured from dc electric conductivities. For the low-temperature gamma-modification, results of two- and three-time (109)Ag correlation spectroscopies provide a detailed insight into the nature of the silver ionic hopping motion. Temperature dependent jump rates measured by two-time correlation functions yield an activation energy E(a)= 0.48 eV. (109)Ag NMR three-time correlation functions indicate that the non-exponential relaxation behavior of the silver ions can be attributed to a broad distribution of jump rates rather than correlated forward-backward jumps. Nevertheless, all the silver ions are mobile down to temperatures of about 185 K.
利用¹⁰⁹Ag、¹²⁵Te和³⁵Cl核磁共振光谱研究了Ag₅Te₂Cl三种多晶型物中结构与离子动力学之间的关系。具体而言，通过温度依赖的¹⁰⁹Ag核磁共振线形和自旋晶格弛豫时间，研究了在240 K附近（P2(1)/c <--> P2(1)/n）和332 K附近（P2(1)/n <--> I4/mcm）观察到的结构相变对银离子迁移率的影响。虽然超离子高温相α-Ag₅Te₂Cl的特征是阳离子亚晶格呈熔融态，但中温相β-Ag₅Te₂Cl中的快速离子动力学发生在包含所有晶体学上不同银位点的空间受限区域。温度依赖的魔角旋转线宽产生的活化能为0.38 eV，与直流电导率测量得到的0.44 eV一致。对于低温γ变体，两次和三次¹⁰⁹Ag相关光谱的结果提供了对银离子跳跃运动本质的详细洞察。通过两次相关函数测量的温度依赖跳跃率产生的活化能E(a)= 0.48 eV。¹⁰⁹Ag核磁共振三次相关函数表明，银离子的非指数弛豫行为可归因于跳跃率的广泛分布，而不是相关的向前-向后跳跃。然而，所有银离子在大约185 K的温度下仍具有流动性。
