Composition-dependent ınterfacial polarization in LaO-modified SnO composite ceramics: structure, surface hydroxylation, and broadband dielectric response

Abstract

SnO2-La2O3 composite powders containing 1, 3, 5, 7, and 10 wt% nominal La2O3 were prepared by a sol-gel-assisted precipitation-dispersion route and examined to determine how phase constitution, surface oxygen chemistry, and microstructural heterogeneity affect the dielectric response. Preformed La2O3 powder was dispersed in an oxidized Sn precursor before alkaline precipitation; this process produced a Sn-rich hydroxide/oxyhydroxide precursor containing a La-derived oxide/hydroxide component and generated a composite architecture rich in phase-boundary and surface-oxygen heterogeneity. X-ray diffraction showed rutile-type tetragonal SnO2 as the dominant phase throughout the series. The nonlinear composition dependence of lattice parameters and unit-cell volume, together with the stable principal SnO2 Raman maximum at 626.7 cm-1, confirms preservation of the rutile SnO2 vibrational framework while indicating La-induced local disorder and phase-boundary modification. FE-SEM/EDX mapping showed La distributed across the analysed micrometre-scale fields and revealed composition-dependent particle-contact development. FT-IR and XPS consistently indicated increasing contributions from hydroxylated, hydrated, and carbonate-containing surface environments as the nominal La2O3 content increased. At 1 kHz, the dielectric constant increased from 11.137 +/- 0.092 for SnO2 to 15.993 +/- 0.064 for Sn-10La(2)O(3), whereas tan delta remained within 0.065-0.070. A Lichtenecker logarithmic volume-mixture benchmark predicted epsilon ' = 11.472 for the 10 wt% composition; the measured value was 39.4% higher than this ideal-mixture estimate. This positive excess permittivity verifies a non-ideal composite dielectric response and supports interfacial/electrical heterogeneity as the origin of the enhancement. The nearly composition-invariant loss-peak position, located in the same intermediate-frequency interval on the order of 104 Hz, indicates that the dominant effective relaxation time remains approximately unchanged, while La2O3 mainly increases the relaxation strength and low-frequency polarization amplitude. The response is therefore assigned to a distributed polarization process involving grain and particle contacts, phase-boundary electrical heterogeneity, electrode interfacial contributions, and hydration-sensitive surface polarization. Within the measured frequency window, Sn-7La(2)O(3) and Sn-10La(2)O(3) provide the most effective balance between enhanced permittivity and controlled dissipation, establishing La2O3-modified SnO2 as a composition-tunable oxide dielectric platform for capacitor-oriented and frequency-sensitive ceramic components.