KBiFe2O5 triggered-phase transition of Bi2Fe4O9 and Fe3O4 in tellurite glass with huge nonlinear and magnetic properties

Abstract

In the quest for glass materials with high nonlinearity and strong magnetism to meet the demands of advancing technology, magnetic nanocrystal (NC) doping emerges as a promising approach. The paper investigates the phase transition from KBiFe₂O₅ to Bi₂Fe₄O₉ and Fe₃O₄ NCs within a TeO₂–Bi₂O₃–B₂O₃ glass matrix. The novelty of this study lies in leveraging the coexistence of multiple phases to amplify both the polarization and magnetic moment of glass. Various techniques, including X-ray diffraction, transition transmission electron microscopy, X-ray photoelectron spectroscopy, Mössbauer spectroscopy, and vibrational sample magnetometer were employed to analyze the impact of NCs content and heat treatment temperature on crystallization, structure modification, and properties. KBiFe₂O₅ NCs doping induces changes in crystal phases and modifies the glass network structure by forming multi-valence states and altering coordination numbers, such as FeO₄→FeO₆, TeO₄→TeO₃, and BO₄→BO₃. Concurrently, appropriate temperature conditions result in reduced NC size, preserving glass transparency and thermal stability. Spinel Fe₃O₄ NCs formation at higher temperatures enhances magnetic behavior. A glass sample containing 1 mol% KBiFe₂O₅ NCs, heat-treated at 410 °C, exhibits a narrow bandgap (E_g) of 1.82 eV, high nonlinear parameters (α₃ = 3.98 × 10⁻¹⁰ m/W, χ⁽³⁾ = 8.65 × 10⁻¹¹ esu), and a low limiting threshold (1.01 × 10¹² W/m²). Additionally, owing to the incorporation of high spin states and active magnetic exchange interactions, the same glass demonstrates robust ferromagnetic behavior (M_s = 2.3 emu/g and H_c = 850 G). The approach developed in this study has been demonstrated to be highly effective in producing transparent glass with promising nonlinearity and magnetic performance suitable for photonics applications.