Interplay between Defects and Cation Nonstoichiometry in Lithium-Substituted CdGa₂O₄ Leading to Multifunctional Behavior

Abstract

Stoichiometric and nonstoichiometric cadmium gallate (gallium-rich) samples have been synthesized by a modified epoxide gel method. Cubic spinel arrangement was inferred for stoichiometric and gallium-rich compositions from powder X-ray diffraction analysis. Complete structural analysis employing Raman spectroscopy has been carried out to find the intricate differences between these two samples. Additional evidence for the cubic symmetry and elemental ratio of these samples has been gathered using microscopy techniques and energy-dispersive X-ray analysis. Li+ substitution for Cd2+ in gallium-rich spinel was examined, and up to 60 mol % of Cd2+ could be substituted with Li+, retaining the spinel arrangement. The introduction of lithium led to a decrease in cubic lattice parameter. Changes in the vibration modes upon lithium substitution were analyzed by Fourier transform infrared and Raman spectral measurements. The band gap value was found to increase with increase in lithium content, indicative of the Burstein–Moss effect in this system. Oxygen vacancies created as a result of lithium substitution was further examined by oxygen-ion conductivity (493–773 K) and dielectric spectroscopic measurements (100–400 K). The estimated activation energy, from these measurements, suggested major contribution of doubly ionized oxygen vacancies to the conductivity in addition to lithium-ion mobility in Li+-substituted samples. A possible defect structure operative in this system has been proposed. The catalytic role of oxygen vacancies as defect centers has been favorably utilized for the photodegradation of aqueous methylene blue dye solution.

Metastable Bi2Zr2O7 with Pyrochlore-like Structure: Stabilization, Oxygen Ion Conductivity, and Catalytic Properties

“…This would lead ultimately to higher dielectric permittivity value. 37 One of the major applications of oxides with fluorite and fluorite-derived structures has been in the area of catalysis. While a major thrust has been centered on the use of fluoritestructured oxides as oxidation catalyst, their capability to promote reduction reactions, preferably organic substrates, has not yet been explored extensively.…”

“…With increase in temperature, the oxygen vacancies could be thermally “ionized”, and their conduction would become dominant due to their mobility, higher vacancy concentration, and higher inertia of oxygen ions. This would lead ultimately to higher dielectric permittivity value …”

Incorporation of Mg2+/Si4+ in ZnGa2O4:Cr3+ to Generate Remarkably Improved Near-Infrared Persistent Luminescence

“…However, Si 4+ ions occupy the tetrahedral sites (Zn sites) in ZnGa 2 O 4 in priority, which leads to the appearance of Ga vacancy with three negative charges and Si 4+ in Zn sites with two positive charges. These defects contribute to the electron traps with a deeper depth more than ~1.0 eV [28,38,39], where the captured electrons cannot easily escape at room temperature and thus contributes to the worse NIR persistent luminescence. Therefore, the most intense and the longest persistent luminescence was observed for x = 0.05 sample, which are the comprehensive outcome from the anti-defects and the defects arising from Si 4+ ions occupying the tetrahedral sites.…”

Electrical properties of barium titanate in presence of Sn2+ dopant

“…With increase in temperature, the oxygen vacancies could be thermally "ionized", their conduction would become dominant due to their mobility, higher vacancy concentration and higher inertia of oxygen ions. This would lead ultimately to higher dielectric permittivity value [19]. So, the high dielectric permittivity of doped samples is due to crystal imperfections formed by doping [20].…”

“…The calculated value of activation energy in the current system might be due to doubly ionized oxygen vacancies. The singly and doubly ionized oxygen vacancies can be calculated according to the following mechanism [19].…”