Varsamis C P E, Makris N, Valvi C, Kamitsos E I
Applied Physics Laboratory, Faculty of Engineering, University of West Attica, 250 Thivon, 112 41 Egaleo, Attica, Greece.
Phys Chem Chem Phys. 2021 Apr 28;23(16):10006-10020. doi: 10.1039/d1cp00301a.
Bismuth-containing borate glasses, xBi2O3-(1 - x)B2O3, were synthesized in the broad composition range 0.20 ≤ x ≤ 0.80 by melting in Pt crucibles and splat-quenching between two metal blocks. Infrared reflectance spectra, measured in the range 30-5000 cm-1, were transformed into absorption coefficient spectra and then deconvoluted into component bands to probe the glass structure as a function of composition. Integrated intensities of bands above 800 cm-1 were used in combination with mass and charge balance equations to quantify the short-range borate structure in terms of the molar fractions X4m, X4o, X3, X2, X1 and X0 for borate units BØ4-, BØ2O23-, BØ3, BØ2O-, BØO22- and BO33-, where Ø and O- denote bridging and non-bridging oxygen atoms. Borate tetrahedral units were found to be present in both the meta-borate, BØ4-, and ortho-borate, BØ2O23-, forms with BØ4- constituting the dominating tetrahedral species for 0.20 ≤ x ≤ 0.70. The BØ2O23- units prevail at higher Bi2O3 levels (x > 0.7), and coexist with their isomeric triangular borate species BO33- (BØ2O23- ⇌ BO33-). The present IR results for the total molar fraction of borate tetrahedral units, X4 = X4m + X4o, are in very good agreement with reported NMR results for the fraction of boron atoms in four-fold coordination, N4. Besides evaluating X4m and X4o, the present work reports also for the first time the fractions of all types of triangular borate species X3-n with n = 0, 1, 2 and 3. The IR region below 550 cm-1 was found to be dominated by the Bi-O vibrational activity in coexisting ionic (160-230 cm-1) and distorted BiO6 sites (330-365 cm-1 and 475-510 cm-1), a result reflecting the dual role of Bi2O3 as glass-modifier and glass-former oxide. The latter role dominates in glasses exceeding 60 mol% Bi2O3, and is consistent with the extended glass formation in the bismuth-borate system. The structural results were used to calculate the average number of bridging B-Ø bonds per boron center, the average Bi-O and B-O single bond energy, and the atomic packing density of the studied glasses. These properties vary approximately linearly with Bi2O3 content in the three regimes 0.2 ≤ x ≤ 0.4, 0.4 < x ≤ 0.6 and 0.6 < x ≤ 0.83, and contribute collectively to the composition dependence of glass transition temperature.
含铋硼酸盐玻璃，xBi₂O₃-(1 - x)B₂O₃，通过在铂坩埚中熔融并在两个金属块之间急冷，在0.20 ≤ x ≤ 0.80的宽组成范围内合成。在30 - 5000 cm⁻¹范围内测量的红外反射光谱被转换为吸收系数光谱，然后解卷积为组分带，以探测作为组成函数的玻璃结构。800 cm⁻¹以上谱带的积分强度与质量和电荷平衡方程结合使用，以硼酸根单元BØ₄⁻、BØ₂O₂³⁻、BØ₃、BØ₂O⁻、BØO₂²⁻和BO₃³⁻的摩尔分数X₄m、X₄o、X₃、X₂、X₁和X₀来量化短程硼酸盐结构，其中Ø和O⁻分别表示桥连和非桥连氧原子。发现硼酸根四面体单元以偏硼酸根BØ₄⁻和原硼酸根BØ₂O₂³⁻两种形式存在，对于0.20 ≤ x ≤ 0.70，BØ₄⁻构成主要的四面体物种。BØ₂O₂³⁻单元在较高的Bi₂O₃含量（x > 0.7）时占主导，并与其异构体三角硼酸根物种BO₃³⁻（BØ₂O₂³⁻ ⇌ BO₃³⁻）共存。目前关于硼酸根四面体单元总摩尔分数X₄ = X₄m + X₄o的红外结果与报道的关于处于四重配位的硼原子分数N₄的核磁共振结果非常吻合。除了评估X₄m和X₄o，本工作还首次报道了所有类型三角硼酸根物种X₃⁻ⁿ（n = 0、1、2和3）的分数。发现550 cm⁻¹以下的红外区域主要由共存的离子型（160 - 230 cm⁻¹）和扭曲的BiO₆位点（330 - 365 cm⁻¹和475 - 510 cm⁻¹）中的Bi - O振动活性主导，这一结果反映了Bi₂O₃作为玻璃改性剂和玻璃形成氧化物的双重作用。后一种作用在Bi₂O₃超过60 mol%的玻璃中占主导，并且与铋硼酸盐系统中扩展的玻璃形成一致。结构结果用于计算每个硼中心的平均桥连B - Ø键数、平均Bi - O和B - O单键能以及所研究玻璃的原子堆积密度。这些性质在0.2 ≤ x ≤ 0.4、0.4 < x ≤ 0.6和0.6 < x ≤ 0.83这三个区域中随Bi₂O₃含量大致呈线性变化，并共同导致玻璃转变温度的组成依赖性。
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