IR, Raman, and NMR Studies of the Short-Range Structures of 0.5Na2S + 0.5[xGeS2 + (1–x)PS5/2] Mixed Glass-Former Glasses

A nonlinear and nonadditive composition-dependent change of the ionic conductivity in mixed glass-former (MGF) glasses when one glass former, such as PS5/2, 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 + PS5/2, 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)PS5/2] 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)PS5/2] glasses using Raman, IR, and 31P MAS NMR spectroscopies. In these studies, it is found that the substitution of PS5/2 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, fNa(P) \u3e 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, fNa(Ge) \u3c 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

Urinary Iodine, Perchlorate, and Thiocyanate Concentrations in U.S. Lactating Women

Background: Iodine is an essential micronutrient for thyroid hormone production. Adequate iodine intake and normal thyroid function are important during early development, and breastfed infants rely on maternal iodine excreted in breast milk for their iodine nutrition. The proportion of women in the United States of childbearing age with urinary iodine concentration (UIC) <50 μg/L has been increasing, and a subset of lactating women may have inadequate iodine intake. UIC may also be influenced by environmental exposure to perchlorate and thiocyanate, competitive inhibitors of iodine transport into thyroid, and lactating mammary glands. Data regarding UIC in U.S. lactating women are limited. To adequately assess the iodine sufficiency of lactating women and potential associations with environmental perchlorate and thiocyanate exposure, we conducted a multicenter, cross-sectional study of urinary iodine, perchlorate, and thiocyanate concentrations in healthy U.S. lactating women. Methods: Lactating women ≥18 years of age were recruited from three U.S. geographic regions: California, Massachusetts, and Ohio/Illinois from November 2008 to June 2016. Demographic information and multivitamin supplements use were obtained. Iodine, perchlorate, and thiocyanate levels were measured from spot urine samples. Correlations between urinary iodine, perchlorate, and thiocyanate levels were determined using Spearman's rank correlation. Multivariable regression models were used to assess predictors of urinary iodine, perchlorate, and thiocyanate levels, and UIC <100 μg/L. Results: A total of 376 subjects (≥125 from each geographic region) were included in the final analyses [mean (SD) age 31.1 (5.6) years, 37% white, 31% black, and 11% Hispanic]. Seventy-seven percent used multivitamin supplements, 5% reported active cigarette smoking, and 45% were exclusively breastfeeding. Median urinary iodine, perchlorate, and thiocyanate concentrations were 143 μg/L, 3.1 μg/L, and 514 μg/L, respectively. One-third of women had UIC <100 μg/L. Spot urinary iodine, perchlorate, and thiocyanate levels all significantly positively correlated to each other. No significant predictors of UIC, UIC <100 μg/L, or urinary perchlorate levels were identified. Smoking, race/ethnicity, and marital status were significant predictors of urinary thiocyanate levels. Conclusion: Lactating women in three U.S. geographic regions are iodine sufficient with an overall median UIC of 143 μg/L. Given ubiquitous exposure to perchlorate and thiocyanate, adequate iodine nutrition should be emphasized, along with consideration to decrease these exposures in lactating women to protect developing infants

Short Range Structural Models of the Glass Transition Temperatures and Densities of 0.5Na2S + 0.5[xGeS2 + (1 – x)PS5/2] Mixed Glass Former Glasses

The 0.5Na2S + 0.5[xGeS2 + (1 – x)PS5/2] mixed glass former (MGF) glass system exhibits a nonlinear and nonadditive negative change in the Na+ ion conductivity as one glass former, PS5/2, is exchanged for the other, GeS2. This behavior, known as the mixed glass former effect (MGFE), is also manifest in a negative deviation from the linear interpolation of the glass transition temperatures (Tg) of the binary end-member glasses, x = 0 and x = 1. Interestingly, the composition dependence of the densities of these ternary MGF glasses reveals a slightly positive MGFE deviation from a linear interpolation of the densities of the binary end-member glasses, x = 0 and x = 1. From our previous studies of the structures of these glasses using IR, Raman, and NMR spectroscopies, we find that a disproportionation reaction occurs between PS7/24- and GeS32- units into PS43- and GeS5/21- units. This disproportionation combined with the formation of Ge4S104- anions from GeS5/21- groups leads to the negative MGFE in Tg. A best-fit model of the Tgs of these glasses was developed to quantify the amount of GeS5/21- units that form Ge4S104- molecular anions in the ternary glasses (∼5–10%). This refined structural model was used to develop a short-range structural model of the molar volumes, which shows that the slight densification of the ternary glasses is due to the improved packing efficiency of the germanium sulfide species.Reprinted with permission from Journal of Physical Chemistry B 118 (2014): 3710, doi: 10.1021/jp411942t. Copyright 2014 American Chemical Society.</p

IR, Raman, and NMR Studies of the Short-Range Structures of 0.5Na2S + 0.5[xGeS2 + (1–x)PS5/2] Mixed Glass-Former Glasses

A nonlinear and nonadditive composition-dependent change of the ionic conductivity in mixed glass-former (MGF) glasses when one glass former, such as PS5/2, 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 + PS5/2, 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)PS5/2] 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)PS5/2] glasses using Raman, IR, and 31P MAS NMR spectroscopies. In these studies, it is found that the substitution of PS5/2 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, fNa(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, fNa(Ge) x. 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.Reprinted with permission from J. Phys. Chem. B, 2014, 118 (7), pp 1943–1953 doi: 10.1021/jp4111053. Copyright 2014 American Chemical Society.</p