engleski

From glass to glass-ceramics: The pivotal role of (micro)structure in enhancing electrical and catalytic properties

Phosphate-based glasses and glass ceramics display remarkable properties that make them suitable materials for various technological applications. Recently, they have attracted special attention as solid electrolytes and/or electrode materials for the development of solid-state batteries. Despite numerous advantages of glassy materials, such as isotropic ionic conduction, lack of grain-boundary effect, and high compositional flexibility, their low electrical conductivity often limits their application. A cost-effective and scalable solution to this issue is the process of thermally induced crystallization, which leads to the formation of glass-ceramic, a composite material consisting of one or more crystalline phases embedded in a glassy matrix. In contrast to homogeneous structure of analogous glasses, glass-ceramics are heterogeneous systems whose macroscopic properties depend largely on microstructural features such as the type, size, distribution, and relative abundance of crystal grains within the amorphous matrix. A powerful technique that facilitates the resolution of electrical processes in complex systems, such as multicomponent phosphate-based glasses and glass ceramics, is Solid-State Impedance Spectroscopy (SS-IS). This method is non-invasive, efficient, and easy to implement, and provides valuable insight into the electrical and dielectric properties of a system under study. The method involves applying a known voltage at different frequencies and measuring the resulting current. The impedance of the system is obtained by changing the excitation frequency across a broad range, from 10–2 Hz to 106 Hz, forming an impedance spectrum. The overall electrical response of the material-electrode system is due to various frequency-dependent microscopic processes, occurring either within the material itself (ion and/or electron transport and polarization) or at the interface between the electrode and the material (the transport or accumulation of charge carriers based on the type of electrode). Consequently, the materials that can be studied using SS-IS range from ionic and mixed ionic-electronic conductors and semiconductors to dielectrics and insulators. In this talk the application of SS-IS will be illustrated through a series of case studies, with a particular focus on phosphate-based glass-(ceramics) systems with different conduction mechanisms: (i) mixed ion-polaron conductive glasses, (ii) mixed glass-network former glasses, (iii) mixed-conductive-mixed-glass-former-systems and (iv) glass-ceramics. Mixed conductive systems that incorporate both mobile alkali ions and transition metal (TM) ions, such as V, Nb, Mo, W, and Fe, have been demonstrated to be highly effective as electrode materials in solid-state batteries. What’s more, since these TMs are generally known to be highly active and selective catalysts in oxidation processes, prepared mixed conductive glasses-(ceramics) materials may be used as heterogeneous catalysts. This opens up new possibilities for the application of TM-containing glassy and glass-ceramic materials in a variety of fields.

phosphate glass ; phosphate glass-ceramic ; electrical properties ; catalytic properties

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