Optimizing microstructure, dielectric performance, and optical characteristics of sodium yttrium copper titanate electroceramics through niobium doping

Abstract

Giant dielectric constant materials are indispensable for the next generation of miniaturized energy storage and electronic devices. However, achieving an optimal balance between high dielectric permittivity, low dielectric loss, and frequency stability remains a major challenge. Here, we report the role of Nb doping in modulating the electrical properties of Na_1/2Y_1/2Cu₃Ti_4-xNb_xO_12+x/2 (NYCTO) electroceramics, establishing detailed structure-property correlations that govern dielectric behavior. A series of Nb-doped NYCTO compositions (x = 0.00–0.15) were synthesized via a systematic solid-state reaction approach and thoroughly characterized. X-ray diffraction confirmed a body-centered cubic perovskite structure, with Nb incorporation inducing lattice expansion and reducing crystallite size. Field emission scanning electron microscopy revealed heterogeneous grain formation, with a strong correlation between grain size and dielectric permittivity. Notably, a colossal dielectric permittivity of ≈ 2.4 × 10⁴ at 20 Hz and 303 K was achieved for x = 0.15, whereas the x = 0.06 composition exhibited the most balanced dielectric performance, with a permittivity of ≈ 1.46 × 10⁴ at 1 kHz, good frequency stability, and a dielectric loss of ≈ 0.24. Impedance spectroscopy analysis confirmed the internal barrier layer capacitor (IBLC) effect as the primary mechanism behind the giant dielectric response. Furthermore, UV–vis spectroscopy revealed a tunable wide bandgap (3.31–3.87 eV) nature in NYCTO, influenced by quantum confinement effects. These findings provide critical insights into the role of Nb doping in tailoring the dielectric and electrical properties of NYCTO to develop high-performance dielectric materials.