Liquid fragility maximum in lithium borate glass‐forming melts related to the local structure
Liquid fragility maximum in lithium borate glass‐forming melts related to the local structure
复制标题
硼酸锂玻璃中液体脆性最大——与局部结构相关的成型熔体
DOI：
10.1111/ijag.16611
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发表时间：
2022
影响因子：
2.1
通讯作者：
Weber, Rick J. K.
中科院分区：
文献类型：
--
作者：
Alderman, Oliver L. G.;Benmore, Chris J.;Reynolds, Bryce;Royle, Brock;Feller, Steve;Weber, Rick J. K.
The structure of liquid lithium pyroborate, Li4B2O5(J= Li/B = 2), has been measured over a wide temperature range by high‐energy X‐ray diffraction, and compared to that of its glass and borate liquids of other compositions. The results indicate a gradual increase in tetrahedral boron fraction from 3(1)% to 6(1)% during cooling fromT= 1271(15) to 721(8) K, consistent with the largerN4= 10(1)% found for the glass, and literature11B nuclear magnetic resonance measurements. van't Hoff analysis based on a simple boron isomerization reaction BØ3O2–⇌ BØO22–yields ΔH= 13(1) kJ mol–1and ΔS= 40(1) J mol–1K–1for the boron coordination change from 4 to 3, which are, respectively, smaller and larger than found for singly charged isomers forJ≤ 1. With these, we extend our model forN4(J,T), nonbridging oxygen fractionfnbr(J,T), configurational heat capacity CPconf(J,T)$C_{\rm{P}}^{{\rm{conf}}}(J,T)$, and entropySconf(J,T) contributions up toJ= 3. A maximum is revealed in CPconf(J,T=Tg)$C_{\rm{P}}^{{\rm{conf}}}(J,T = {T_{\rm{g}}})$ atJ= 1, and shown semi‐quantitatively to lead to a corresponding maximum in fragility contribution, akin to that observed in the total fragilities by temperature‐modulated differential scanning calorimetry. Lithium is bound to 4.6(2) oxygen in the pyroborate liquid, with 2.7(1) bonds centered around 1.946(8) Å and 1.9(1) around 2.42(1) Å. In the glass,nLiO= 5.4(4), the increase being due to an increase in the number of short Li–O bonds.
The structure of liquid lithium pyroborate, Li4B2O5(J= Li/B = 2), has been measured over a wide temperature range by high‐energy X‐ray diffraction, and compared to that of its glass and borate liquids of other compositions. The results indicate a gradual increase in tetrahedral boron fraction from 3(1)% to 6(1)% during cooling fromT= 1271(15) to 721(8) K, consistent with the largerN4= 10(1)% found for the glass, and literature11B nuclear magnetic resonance measurements. van't Hoff analysis based on a simple boron isomerization reaction BØ3O2–⇌ BØO22–yields ΔH= 13(1) kJ mol–1and ΔS= 40(1) J mol–1K–1for the boron coordination change from 4 to 3, which are, respectively, smaller and larger than found for singly charged isomers forJ≤ 1. With these, we extend our model forN4(J,T), nonbridging oxygen fractionfnbr(J,T), configurational heat capacity CPconf(J,T)$C_{\rm{P}}^{{\rm{conf}}}(J,T)$, and entropySconf(J,T) contributions up toJ= 3. A maximum is revealed in CPconf(J,T=Tg)$C_{\rm{P}}^{{\rm{conf}}}(J,T = {T_{\rm{g}}})$ atJ= 1, and shown semi‐quantitatively to lead to a corresponding maximum in fragility contribution, akin to that observed in the total fragilities by temperature‐modulated differential scanning calorimetry. Lithium is bound to 4.6(2) oxygen in the pyroborate liquid, with 2.7(1) bonds centered around 1.946(8) Å and 1.9(1) around 2.42(1) Å. In the glass,nLiO= 5.4(4), the increase being due to an increase in the number of short Li–O bonds.