A review: A new insight for electronic polarizability and chemical bond strength in Bi₂O₃-based glasses

Highlights

• Bi₂O₃-based glasses exhibit an extremely strong basic nature with large optical basicities Λ(n_o).

• Bi₂O₃-based glasses have an extremely weak chemical bond strength with small interionic interaction parameters A(n_o).

• A good correlation between Λ(n_o) and A(n_o) is present.

• Outstanding properties of Bi₂O₃-based glasses are understood from large Λ(n_o) and small A(n_o) values.

Abstract

Bismuth oxide (Bi₂O₃)-based glasses showing outstanding properties such as high linear refractive indices, low glass transition temperatures, and high third-order nonlinear optical susceptibilities are promising materials for low temperature melting and photonic device applications. The present article reviews the current status of the electronic polarizability in Bi₂O₃-based glasses with glass-forming oxides and modifiers through the refractive index-based optical basicity Λ(n_o) and interionic interaction parameter A(n_o) in to understand deeply the uniqueness of Bi₂O₃-based glasses among other oxide glasses. The values of Λ(n_o), and A(n_o) in some Bi₂O₃-based glasses were estimated newly in this article. It was clarified that Bi₂O₃-based glasses exhibit an extremely strong basic nature with Λ(n_o)∼1.15 and extremely weak chemical bond strength with A(n_o)∼0.01 Å⁻³ among oxide glasses, being more basic compared with TeO₂-based glasses with Λ(n_o)∼1.0 and A(n_o)∼0.03 Å⁻³. The outstanding properties of Bi₂O₃-based glasses were discussed from the viewpoints of electronic polarizability and weak chemical bond strength.

Introduction

Today, it is widely recognized that bismuth oxide (Bi₂O₃) is one of the most important constituents for the design and control of thermal and optical properties of oxide glasses. In particular, Bi₂O₃-based glasses are promising and innovative materials for low temperature melting sealing applications and photonic devices, because they show excellent properties such as low glass transition temperatures (T_g), high linear refractive indices (n_o), narrow optical band gaps, wide infrared (IR) transmissions, low phonon energies, and large third-order optical nonlinearities [1,2]. Bi₂O₃ oxide belongs to the category of the so-called “conditional glass-forming oxides”, and various Bi₂O₃-based glasses have been realized in the combination with other oxides. For example, Bi₂O₃-B₂O₃ and Na₂O-Bi₂O₃-B₂O₃ glasses reported by Bishay and Maghrabi [3], Bi₂O₃-SiO₂-B₂O₃ glasses by Kokubo and Ikeda [4], PbO-Bi₂O₃-Ga₂O₃ glasses by Dumbaugh [5,6], Li₂O-BaO-Bi₂O₃ glasses by Fu [7], and Bi₂O₃-CaO-SrO-CuO glasses by Komatsu et al. [8] would be the pioneering work for the glass formation in the early stage of the research of Bi₂O₃-based glasses.

One of the most important properties of materials, which is closely related to their applicability in the field of optics and electronics, is the electronic polarizability. After the pioneering work on the electronic polarizability of glasses, i.e., optical basicity, by Duffy and Ingram [9,10], optical basicity has been recognized as an important issue in the science and technology of glasses. For instance, Dimitrov and Komatsu [11], [12], [13], [14], [15], [16] proposed the classification (characterization) concept in oxide glasses from the degree of optical basicity and approached more deeply the electronic polarizability of glasses from the viewpoints of the interionic interaction parameter for cation and anion (oxygen) pairs being a good measure for the chemical bond strength of glasses. It is of extremely importance to evaluate optical basicity and interionic interaction parameter of glasses and also to clarify the correlation between optical basicity/interionic interaction parameter and structure/property in various glasses for development of new functional glasses. The optical basicity and interionic interaction parameter of some Bi₂O₃-based glasses such as Bi₂O₃-B₂O₃ and ZnO-Bi₂O₃-B₂O₃ glasses have been studied extensively, leading to a deep understanding of the features of electronic polarizability and chemical bonding characters of Bi₂O₃-based glasses [17], [18], [19], [20], [21], [22].

In this review article, we evaluate the values of optical basicity and interionic interaction parameter in different Bi₂O₃-based glasses reported so far and draw out the intrinsic features of electronic polarizability and chemical bonding state. We also approach unique and outstanding properties of Bi₂O₃-based glasses from the viewpoints of electronic polarizability. Recently, the features of the electronic polarizability and chemical bonding strength and also the related properties such as the glass transition temperature of TeO₂-based glasses have been discussed [23]. It is of interest to compare the electronic polarizability of Bi₂O₃-based and TeO₂-based glasses, because both oxides Bi₂O₃ and TeO₂ known as the conditional glass-forming oxides have basic nature and are key components for photonic device applications. It is also of importance to compare the electronic polarizability of Bi₂O₃-based glasses and other B₂O₃-, SiO₂-, P₂O₅-, and GeO₂-based glasses with no Bi₂O₃, which will clarify more the features and uniqueness of Bi₂O₃-based glasses. In this review, the values of the electronic polarizability of Bi₂O₃-based glasses are estimated using the equations based on the Lorentz-Lorenz formula, and, therefore, Bi₂O₃-based glasses having (reported) the values of density and linear refractive index are mainly analyzed. To the best our knowledge, two review papers on Bi₂O₃-based glasses have been published so far, in which the low temperature meting behavior and photonic device applications are the main focus [1,2]. The present article will provide a new insight on the role of Bi₂O₃ in oxide glasses, leading to the design of innovative oxide glasses.