A-site acceptor doped LaNbO4 thin film formation and structural investigation

In this paper, doped La1-xAxNbO4 (A = Ca, Mg) thin films were formed using electron beam vapor deposition. The influence of the doping concentration of A site dopants (A = Ca, Mg) on the thin ceramics surface microstructure, morphology and electrical properties, including the charge carrier mobility and diffusion coefficient, was studied. It was found that the formed thin films are dense (>96 %) and have homogenous nanocrystalline structure composed of the tetragonal LaNbO4 phase. The total conductivity of the formed thin films is in 10-3 S/cm range for Ca-doped LaNbO4 and 10-4 S/cm range for Mg-doped LaNbO4 at 800 °C under wet H2 reducing atmosphere. The nature of protonic conduction was confirmed by the isotopic effect. The calculated ΔHmob,H is 57 kJ/mol at 650 °C for the La0.995Ca0.005NbO4 film, which total conductivity was highest in the present study (9.52∙10-3 S/cm at 800 °C under wet H2 reducing atmosphere). ΔHmob,H increases steadily with increasing the dopants’ concentration from 57 kJ/mol to 84 kJ/mol. The charge mobility decreases from 2.32×10-5 cm2/V∙s to 6.25×10-7 cm2/V∙s as the dopants’ concentration increases at 650 °C.