Buannic Lucienne, Sperrin Luke, Dervişoğlu Riza, Blanc Frédéric, Grey Clare P
Department of Chemistry, Stony Brook University, Stony Brook, NY 11790-3400, USA.
Phys Chem Chem Phys. 2018 Feb 7;20(6):4317-4328. doi: 10.1039/c7cp08523k.
Perovskite-based material Sc-doped BaZrO is a promising protonic conductor but with substantially lower conductivities than its Y-doped counterpart. H solid-state NMR spectroscopy in combination with DFT modelling was used to analyze the protonic distribution in BaZrScO(OH) and its effect on charge carrier mobility. H single pulse and H-Sc TRAPDOR MAS NMR experiments highlighted the mobile character of the proton charge carriers at room temperature, giving rise to a single broad resonance, protons hopping between multiple sites on the NMR timescale. At low temperatures, the protonic motion was successfully slowed down allowing direct observation of the various proton environments present in the structure. For x ≤ 0.15, DFT modelling suggested a tendency for strong dopant-proton association leading to Sc-OH-Zr environments with H NMR shifts of 4.8 ppm. The Zr-OH-Zr environment, H-bonded to a Sc-O-Zr, lies 32 kJ mol higher in energy than the Sc-OH-Zr environment, suggesting that the Sc-OH-Zr environment is trapped. However, even at these low concentrations, Sc-Sc clustering could not be ruled out as additional proton environments with stronger H-Sc dipolar couplings were observed (at 4.2 and 2.8 ppm). For x = 0.25, DFT modelling on the dry material predicted that Sc-□-Sc environments were extremely stable, again highlighting the likelihood of dopant clustering. A large number of possible configurations exists in the hydrated material, giving rise to a large distribution in H chemical shifts and multiple conduction pathways. The H shift was found to be strongly related to the length of the O-H bond and, in turn, to the hydrogen bonding and OOH distances. The breadth of the NMR signal observed at low temperature for x = 0.30 indicated a large range of different OH environments, those with lower shifts being generally closer to more than one Sc dopant. Lower DFT energy structures were generally associated with weaker H-bonding environments. Both the calculations and the DFT modelling indicated that the protons tend to strongly bond to the Sc clusters, which, in conjunction with the higher energies of configurations containing Zr-OH-Zr groups, could help explain the lower conductivities recorded for the Sc-substituted BaZrO in comparison to its yttrium counterpart.
基于钙钛矿的材料Sc掺杂BaZrO是一种很有前景的质子导体，但其电导率远低于Y掺杂的同类材料。采用H固体核磁共振光谱结合密度泛函理论（DFT）建模来分析BaZrScO(OH)中的质子分布及其对载流子迁移率的影响。H单脉冲和H-Sc TRAPDOR MAS NMR实验突出了室温下质子载流子的移动特性，产生了一个单一的宽共振峰，质子在核磁共振时间尺度内在多个位点之间跳跃。在低温下，质子运动成功减缓，从而能够直接观察到结构中存在的各种质子环境。对于x≤0.15，DFT建模表明存在强掺杂剂-质子缔合的趋势，导致形成Sc-OH-Zr环境，其H NMR位移为4.8 ppm。与Sc-O-Zr氢键相连的Zr-OH-Zr环境，其能量比Sc-OH-Zr环境高32 kJ/mol，这表明Sc-OH-Zr环境被捕获。然而，即使在这些低浓度下，也不能排除Sc-Sc簇的存在，因为观察到了具有更强H-Sc偶极耦合的额外质子环境（在4.2和2.8 ppm处）。对于x = 0.25，对干燥材料的DFT建模预测Sc-□-Sc环境极其稳定，再次突出了掺杂剂簇集的可能性。水合材料中存在大量可能的构型，导致H化学位移有很大分布和多种传导途径。发现H位移与O-H键的长度密切相关，并进而与氢键和OOH距离相关。对于x = 0.30，在低温下观察到的NMR信号宽度表明存在大范围不同的OH环境，位移较低的那些环境通常更靠近不止一个Sc掺杂剂。较低的DFT能量结构通常与较弱的氢键环境相关。计算和DFT建模均表明，质子倾向于与Sc簇强烈结合，这与含有Zr-OH-Zr基团的构型具有更高能量一起，有助于解释与钇取代的BaZrO相比，Sc取代的BaZrO记录到的较低电导率。
