The Effect of La Doping on the Structure, Lattice Dynamics, and Optional Bandgap of NaNbO ₃ Ceramics

This article systematically investigates the effects of La doping on the crystal structure, lattice dynamics, and optical properties of NaLaNbO ceramics. X–ray diffraction and Rietveld refinement reveal that the material undergoes a phase transformation from the orthorhombic Q‐phase to a tetragonal phase with increasing La doping concentration. Raman and infrared spectroscopy reveal the softening and degeneracy of mid‐frequency phonons, induced by the bending vibrations of NbO octahedra during the phase transition, reflecting an increase in the NbONb bond angle and the release of lattice strain. Spectroscopic ellipsometry analysis reveals that the optical bandgap exhibits a nonmonotonic “V‐shaped” variation with doping. The initial narrowing originates from the introduction of defect levels, while the bandgap widening at the critical concentration of = 0.10 is associated with a reorganization of the electronic density of states. This article confirms that La doping can synergistically regulate the structural phase transition and optoelectronic properties of NaNbO through the combined effects of size mismatch and defect chemistry, providing important guidance for the design of high‐performance lead‐free ferroelectric materials.