Glass is one of the most important and promising types of materials. It is characterized by high natural, physical, chemical, mechanical, and optical properties [1]. These properties extend to the possibility of adapting it for use in various industrial, military, biological, and environmental fields. The most important of them is phosphate glass, which is mainly dependent on phosphorous penta-oxide (P2O5). Glass systems based on P2O5 are appealing materials because of their remarkable properties, which include a low melting point, a low glass transition temperature, a low refractive index, a high coefficient of thermal expansion, and high transparency over a large spectral range [2, 3]. Thus, it can be used in a wide range of fields, were several scholars and experts have investigated it for the past decades [2–9]. For instance, glass fibers [4], bioglasses [5, 6], glass-to-metal seals [7], high-radioactive nuclear waste [8], and glass-polymer composites [9]. Unfortunately, phosphate glass typically has low chemical stability, which severely restricts its use [10]. It has been demonstrated that adding various oxides, in particular, transition metals and/or rare earth oxides, to phosphate glasses can improve their chemical stability, and furthermore iron oxide [11–13]. The phosphate-based glass systems containing higher amounts of transition metal or rare earth ions are also amorphous, unlike other types of glasses [14].
In light of these, numerous additional metal oxides, including Al2O3, ZnO, Sc2O3, Ga2O3, CaO, In2O3, MnO, TiO2 among others, were added and found to be effective phosphate glass stabilizers. For example, zinc oxide (ZnO) is one of the oxides that have been used to increase the phosphate glasses' chemical stability [15]. Glass contains ZnO, which is known as an intermediate oxide, since Zn2+ has a high ion radius and an electronic structure with 18 outer-shell electrons [16]. It can cross-link the phosphate chains by creating P–O–Zn bridges [17] or join the glass network by producing [ZnO4] units [18]. Thus, zinc oxide deserves to be an additional glass modifier due to its pronounced effects on the glassy networks [19]. On the other hand, iron phosphate glasses' thermal characteristics are enhanced by the addition of BaO, particularly their chemical durability. Iron phosphate glasses show extremely high chemical durability, excellent thermal stability, a low melting temperature, and a wide glass forming region as a result of the incorporation of BaO [20].
Additionally, phosphate glasses undergo changes in structure as Fe2O3 is added to their backbone structures [21–23]. They can act as a glass network former and/or modifier through generating FeO4 and/or FeO6 units, respectively. This increases the cross-linking between glass chains by replacing the readily hydrated P–O–P connections with P–O–Fe3+ and/or P–O–Fe2+ links. As a result, oxide glasses are synthesized with excellent chemical stability, low corrosion rates, and relatively low melting temperatures [21–25]. While, the band gap structure of phosphate glasses may be affected by adding Fe2O3, thus their semiconducting features [23, 26–28]. In oxide glasses, O2− anions in the glass matrix may coordinate the alkaline earth and transition metal ions octahedral or tetrahedral [12, 13]. Furthermore, adding Fe2O3 has been observed to turn the glass color from brown to black, decreasing its usefulness for visible-spectrum optical applications [29].
Among several oxides, indium oxide (ln2O3) is shown to be highly soluble in phosphate-based glasses, improves aqueous corrosion by a factor of 1000, and significantly increases transparency [30]. Indium is an elevated conductance element with a broad optical band gap, an n–type semiconductor, of 3.7 eV for direct band gaps and 2.6 eV for indirect band gaps [31]. These characteristics make it extremely relevant for many technological applications which including touch screens, liquid crystal display (LCD), solar energy systems, sensors, photodiodes, transparent contacts, and reflective surfaces for solar cells, among other electronic devices [32]. Nevertheless, the majority of research on In2O3 combination materials is limited, particularly when it comes to the optical and gamma-rays shielding properties of In2O3–containing bulk glasses, which are extremely rare [31]. Investigating the impact of In2O3 on the structural, mechanical, and other related properties of Fe2O3-mixed multi-component Na2O–BaO–ZnO–P2O5 glasses is the main goal of this research. The study involved evaluating the density, molar volume, Tg and Tp characteristic temperatures, and elastic parameters. XRD and DSC techniques were also applied.