Indium containing sillenite semiconductor: Synthesis,structural, spectroscopic,and thermogravimetric analysis

Sillenite-type ceramics are non-centrosymmetric phases of ongoing research interest because of their structural defects and optoelectronic properties. We report a series of sillenite compounds with a general composition Bi₁₂(Bi³⁺_4/5−3xIn³⁺_5x□_1/5−2x)O_19.2+3x□_0.8−3x for x = 0.03–0.27 to understand how the crystal–physicochemical properties change with a successive filling of empty Bi³⁺ positions in the tetrahedral site by In³⁺ cation. Conventional solid-state synthesis method is used to prepare the microcrystalline samples. Each sample is characterized by X-ray diffraction, Raman, UV/Vis diffuse reflectance spectroscopy, and thermogravimetry (TG/DSC). X-ray powder data Rietveld refinement reveals that phase-pure samples can be obtained for x = 0.03–0.08 in the space group I23. Appearance of starting In₂O₃ as minor phases with the final products for 0.10 < x < 0.27 suggests for x_max = 0.08. The successive decrease of the lattice parameter indicates the incorporation of smaller In³⁺ cations in the structure. The effect of the lone electron pairs of Bi³⁺ and the structural cation vacancies lead to the modification of the interatomic bond lengths. At least one Raman active phonon mode shows hardening for decreasing cation vacancy concentration in the system. The bandgap energy increases with increasing indium content. An additional absorption band at lower energy for x = 0.03–0.08 complements the theoretical study, which completely disappears for x > 0.08. The stronger In–O bonds play pivotal roles in the thermal stability of the phases studied by TGA/DSC analysis.