Abstract Investigating the length-scales of order in glasses is important to understand glass properties and hence, the underlying glass structure. Addition of alkali oxides (M2O) in tellurite glass is well-known to modify its network and alter properties by conversion of its basic structural units of TeO4 → TeO3 and increasing the conversion upon further addition of M2O. In this study, we report results of our Raman and Brillouin scattering investigations on 0.12M2O:0.88TeO2 (M = Li, Na, K, Rb and Cs) glasses with an aim to study the effect of the specific alkali cation (M) at fixed composition, on the resulting network structure that determines their interesting optical properties. The network-polyhedral (TeO3) stretching vibrations exhibits red-shift while the Te–O–Te bending mode blue-shifts as M varies from Li to Cs. The fraction of terminal TeO4 units increase steeply with respect to TeO3 and also at the cost of TeO4 units within the network chains, with increasing size of M, contrary to earlier predictions that at fixed concentration of M2O, only the interactions between alkali cation (M) and anions of structural units change, keeping the network structure unaltered. A reduction in frequency with rising mass of M was observed for the Brillouin modes and the Boson peak. Combining results from these techniques, probing structure at different length-scales, depicts that even though increasing M size lowers the conversion of TeO4 to TeO3 units, still the network disintegrates further since the fraction of TeO4 with non-bridging oxygens (NBOs) enhance. This causes reduction in elastic modulus at a larger length-scale, even though specific intra-molecular interactions become stronger within the glass network. The increasing size of the cation from Li+ to Cs+, while preserving the charge of the alkali ion, helps distribute the same electric charge on larger number of anionic tellurite units of the network, and thus, enlarges the correlation length with M, while simultaneously decreasing the network strength. These observations provide evidence for the structural changes leading to the enhanced densities, increased band gaps, reduced refractive indices and the earlier-reported reduction in non-linear susceptibilities with increasing size and mass of M.

中文翻译：

---

了解碱金属氧化物诱导亚碲酸盐玻璃中不同长度尺度的结构改性以改善光学性能

摘要 研究玻璃中有序的长度尺度对于理解玻璃特性以及潜在的玻璃结构很重要。众所周知，在碲酸盐玻璃中添加碱金属氧化物 (M2O) 可以通过转化其基本结构单元 TeO4 → TeO3 并在进一步添加 M2O 时提高转化率来修改其网络并改变性能。在本研究中，我们报告了对 0.12M2O:0.88TeO2（M = Li、Na、K、Rb 和 Cs）玻璃的拉曼和布里渊散射研究结果，目的是研究特定碱金属阳离子 (M) 在固定组成，在由此产生的网络结构上，决定了它们有趣的光学特性。网络-多面体 (TeO3) 伸缩振动表现出红移，而 Te-O-Te 弯曲模式随着 M 从 Li 变为 Cs 发生蓝移。末端 TeO4 单元的比例相对于 TeO3 急剧增加，并且以网络链内 TeO4 单元为代价，随着 M 的大小增加，与早先的预测相反，在固定浓度的 M2O 下，只有碱金属阳离子（M ) 和结构单元的阴离子发生变化，保持网络结构不变。观察到布里渊模式和玻色子峰的频率随着 M 质量的增加而降低。结合这些技术的结果，在不同长度尺度上探测结构，表明即使增加 M 尺寸会降低 TeO4 到 TeO3 单元的转化率，但由于 TeO4 与非桥接氧 (NBO) 的分数增加，网络仍然进一步瓦解。这会导致更大长度范围内弹性模量的降低，即使特定的分子内相互作用在玻璃网络中变得更强。阳离子从 Li+ 到 Cs+ 的大小增加，同时保留碱离子的电荷，有助于将相同的电荷分布在网络的更多阴离子亚碲酸盐单元上，从而扩大与 M 的相关长度，同时降低网络强度。这些观察结果为导致密度增加、带隙增加、折射率降低以及早先报道的非线性磁化率随着 M 的大小和质量的增加而降低的结构变化提供了证据。有助于将相同的电荷分布在网络的大量阴离子亚碲酸盐单元上，从而扩大与 M 的相关长度，同时降低网络强度。这些观察结果为导致密度增加、带隙增加、折射率降低以及早先报道的非线性磁化率随着 M 的大小和质量的增加而降低的结构变化提供了证据。有助于将相同的电荷分布在网络的大量阴离子亚碲酸盐单元上，从而扩大与 M 的相关长度，同时降低网络强度。这些观察结果为导致密度增加、带隙增加、折射率降低以及早先报道的非线性磁化率随着 M 的大小和质量的增加而降低的结构变化提供了证据。