Structural, Optical, and Dielectric Properties of Bi1.5–xZn0.92–yNb1.5O6.92−δ Thin Films Grown by PLD on R-plane Sapphire and LaAlO3 Substrates

Bi1.5–xZn0.92–yNb1.5O6.92−δ thin films have the potential to be implemented in microwave devices. This work aims to establish the effect of the substrate and of the grain size on the optical and dielectric properties. Bi1.5–xZn0.92–yNb1.5O6.92−δ thin films were grown at 700 °C via pulsed-laser deposition on R-plane sapphire and (100)pc LaAlO3 substrates at various oxygen pressures (30, 50, and 70 Pa). The structure, morphology, dielectric and optical properties were investigated. Despite bismuth and zinc deficiencies, with respect to the Bi1.5Zn0.92Nb1.5O6.92 stoichiometry, the films show the expected cubic pyrochlore structure with a (100) epitaxial-like growth. Different morphologies and related optical and dielectric properties were achieved, depending on the substrate and the oxygen pressure. In contrast to thin films grown on (100)pc LaAlO3, the films deposited on R-plane sapphire are characterized by a graded refractive index along the layer thickness. The refractive index (n) at 630 nm and the rela...