Systematic Replacement of PbO by BaO for TGG Single Crystal Production Using the Supersaturated Glass-Melt Method

This study demonstrates the controlled nucleation and growth of high-quality terbium gallium garnet (TGG, Tb3Ga5O12) single crystals in PbO-free BaO-based glass ceramics through a sustainable supersaturated glass-melt approach. Using a new multicomponent glass composition and optimized thermal treatments, controlled nucleation and growth of well-defined cubic TGG crystals (5−50 μm) were achieved within the glass matrix while maintaining high optical transparency. Structural characterization by powder and single-crystal X-ray diffraction confirmed the formation of phase-pure TGG cubic garnet (space group Ia3̅d) with lattice parameters consistent with reference TGG crystals. Raman and FTIR spectroscopy verified the preservation of the garnet structure, while SEM−EDS analysis revealed a homogeneous elemental distribution between the crystalline phase and the surrounding glass matrix. Optical measurements showed good transparency across the visible and near-infrared regions, characteristic of TGG materials. Magnetic characterization of the Pb-free composition exhibited typical paramagnetic behavior, with Curie−Weiss analysis yielding an effective magnetic moment (μeff ≈ 9.62 μB) close to the theoretical value for Tb3+ ions and indicating weak antiferromagnetic interactions (θ = −5.78 K). These results demonstrate that BaO can successfully replace PbO without altering the structural or magnetic properties of TGG, providing an environmentally safer route for producing TGG crystals for magneto-optical applications.