Synthesis, microstructural, rietveld refinement and optical characterizations of sol–gel grown cerium oxide ceramics

Abstract

The cerium oxide (CeO₂) ceramics have been synthesized in the current study by employing the sol–gel technique. Synthesized CeO₂ ceramics were eyed for their crystal structure and phase purity using X-ray diffraction (XRD). The crystallographic space group (SG) of synthesized CeO₂ ceramic is $fm\overline{3 }m (225)$, with a single-phase cubic structure. The CeO₂ ceramic’s stacking fault morals for the most intense peaks have been calculated ($8.5325\times {10}^{-4}$). A value of unity was obtained for the favored orientation of the crystallites along a crystal plane (hkl) by measuring the texture coefficient (C_i) of each XRD peak of the CeO₂ ceramic. Based on the calculations, the CeO₂ ceramic has a degree of preferred orientation (σ) of 0.1566. The lattice constant for CeO₂ ceramics is 0.5375 nm, which yields a cell volume of 0.1585 nm³ using Miller indices for the prime (1 1 1) plane. Bravais’s theory calculates the distance between crystal planes (d_hkl) to understand material growth and infers the significance of CeO₂’s (1 1 1) plane. Fullprof suite Rietveld refines XRD data. Numerous methods such as Nelson–Riley (N–R), Scherrer, Stokes–Wilson (S–W), Monshi, Williamson–Smallman (W–S), Williamson–Hall (W–H), size-strain plot (SSP) and Halder–Wagner (H–W) methods have determined CeO₂ ceramic’s microstructural parameters such as lattice constant (a), the crystallite size (D), strain ($\varepsilon$), dislocation density (δ), stress (σ), Young’s modulus (Y), and energy density (u). Elemental map** analysis was used to determine the elemental distribution of synthesized CeO₂ ceramics. Pycnometers confirmed CeO₂’s density (7.2089 gm-cm⁻³). Fourier transform infrared (FTIR) spectroscopy found an intense band near 1020 cm⁻¹, indicating C=C stretching mode and double bonds in CeO₂ ceramics. The UV–VIS–NIR spectrometer recorded CeO₂ ceramics’ reflectance spectra at room temperature. The absorption spectra display a pair of clearly visible peaks at 242 and 374 nm. The optical spectra of CeO₂ ceramics reveal extinction coefficient (k) and refractive index (η) of $0.2016\times {10}^{-4}$ and 2.40 at characteristic wavelength (λ_c = 374 nm). Tauc and Kubelka–Munk’s methods determined CeO₂ ceramic’s optical bandgap (E_g = 3.32 eV). Near λ_c, the imaginary (${\varepsilon }_{i}$) and real (${\varepsilon }_{r}$) dielectric constants are $9.5457\times {10}^{-4}$ and 5.7549, respectively, and the dissipation factor (tan δ) value is 1.6569 × 10^–4. Optical (σ_o) and electrical (${\sigma }_{e}$) conductivity maxima and minima for CeO₂ ceramics occur at 3.34 eV. The values of Urbach’s energy (E_U) and Urbach absorption coefficient (${\alpha }_{0}$) for CeO₂ are 0.5006 eV and 0.9176 m⁻¹, respectively. The VELF and SELF measurements of electron energy loss showcase the prerequisite CeO₂ peaks at 3.3423 and 4.9600 eV, respectively. CeO₂ ceramics emit UV-Blue under UV excitation and are elucidated by the electron transition in photoluminescence at room temperature. The implications are addressed.