Bischoff Christian, Schuller Katherine, Dunlap Nathan, Martin Steve W
Department of Materials Science and Engineering, Iowa State University of Science & Technology , Ames, Iowa 50011, United States.
J Phys Chem B. 2014 Feb 20;118(7):1943-53. doi: 10.1021/jp4111053. Epub 2014 Feb 10.
A nonlinear and nonadditive composition-dependent change of the ionic conductivity in mixed glass-former (MGF) glasses when one glass former, such as PS(5/2), is replaced by a second glass former, such as GeS2, at constant alkali modifier concentrations, such as Na2S, is known as the mixed glass-former effect (MGFE). Alkali ion conducting glasses are of particular interest for use as solid electrolytes in alkali-based all-solid-state batteries because sulfide amorphous materials have significantly higher alkali ion conductivities than their oxide glass counterparts. In this study of the ternary MGF system Na2S + GeS2 + PS(5/2), we report the careful structural characterization of these glasses using a combination of vibrational, infrared (IR), Raman, and nuclear magnetic resonance (NMR) spectroscopies. Our measurements of the 0.5Na2S + 0.5[xGeS2 + (1-x)PS(5/2)] MGF system show that this glass system exhibits a strongly negative MGFE and non-Arrhenius ionic conductivities. While this negative MGFE in the Na(+) ion conductivity makes these glasses less attractive for use in solid-state Na batteries, the structural origin of this effect is important to better understand the mechanisms of ion conduction in the glassy state. For these reasons, we have examined the structures of ternary 0.5Na2S + 0.5[xGeS2 + (1-x)PS(5/2)] glasses using Raman, IR, and (31)P MAS NMR spectroscopies. In these studies, it is found that the substitution of PS(5/2) by GeS2, that is, increasing x, leads to unequal sharing of the Na(+) in these glasses. Thus, in all MGF compositions, phosphorus groups are associated with a disproportionately larger fraction, f(Na(P)) > 0.5(1 - x), of the Na(+) ions while the germanium groups are found to be Na(+)-deficient relative to the total amount of Na(+) present in the glass, that is, f(Na(Ge)) < 0.5x. From the spectroscopic study of these glasses, a short-range order (SRO) structural model is developed for these glasses and is based on the germanium and phosphorus SRO groups in these glasses as a first step in understanding the unique negative MGFE and non-Arrhenius behavior in the Na(+) ion conductivity in these glasses.
在混合玻璃形成体（MGF）玻璃中，当一种玻璃形成体（如PS(5/2)）在恒定碱改性剂浓度（如Na2S）下被另一种玻璃形成体（如GeS2）取代时，离子电导率会发生非线性且非加和性的成分依赖性变化，这种现象被称为混合玻璃形成体效应（MGFE）。碱离子传导玻璃作为碱基金属全固态电池中的固体电解质特别受关注，因为硫化物非晶材料的碱离子电导率比其氧化物玻璃对应物显著更高。在对三元MGF体系Na2S + GeS2 + PS(5/2)的这项研究中，我们报告了使用振动光谱、红外（IR）光谱、拉曼光谱和核磁共振（NMR）光谱相结合的方法对这些玻璃进行的细致结构表征。我们对0.5Na2S + 0.5[xGeS2 + (1 - x)PS(5/2)] MGF体系的测量表明，该玻璃体系表现出强烈的负MGFE和非阿累尼乌斯离子电导率。虽然Na(+)离子电导率中的这种负MGFE使得这些玻璃在固态钠电池中的应用吸引力降低，但这种效应的结构起源对于更好地理解玻璃态中离子传导机制很重要。出于这些原因，我们使用拉曼光谱、IR光谱和(31)P MAS NMR光谱研究了三元0.5Na2S + 0.5[xGeS2 + (1 - x)PS(5/2)]玻璃的结构。在这些研究中发现，用GeS2取代PS(5/2)，即增加x，会导致这些玻璃中Na(+)的分配不均。因此，在所有MGF成分中，磷基团与不成比例的较大部分Na(+)离子相关联，f(Na(P)) > 0.5(1 - x)，而相对于玻璃中存在的Na(+)总量，锗基团被发现缺乏Na(+)，即f(Na(Ge)) < 0.5x。通过对这些玻璃的光谱研究，基于这些玻璃中的锗和磷短程有序（SRO）基团，为这些玻璃建立了一个SRO结构模型，这是理解这些玻璃中独特的负MGFE和Na(+)离子电导率的非阿累尼乌斯行为的第一步。
