Deciphering the cooperative mechanisms of La doping, temperature, and pressure in NaNbO $$_{3}$$ ceramics: a multi-stimuli Raman spectroscopic study

NaNbO \(_{3}\) , as a typical lead-free perovskite ferroelectric, holds great potential for energy storage and electromechanical applications, whereas the synergistic regulation of lattice dynamics by La doping, temperature, and pressure remains poorly understood. Here, we systematically investigate La \(^{3+}\) -doped NaNbO \(_{3}\) ceramics via Rietveld refinement and multi-stimuli Raman spectroscopy. La \(^{3+}\) substitution induces lattice distortion and oxygen vacancies, driving a structural transition from an ordered orthorhombic ferroelectric phase to a disordered ergodic relaxor state, where \(\textit{x}\) = 0.08 serves as a metastable boundary with maximal lattice disorder and superior external-field sensitivity. Temperature-dependent Raman results reveal a successive \(\textrm{NR} \rightarrow \textrm{ER} \rightarrow \textrm{SPE}\) structural evolution, while variable-pressure Raman identifies a unique B-site order–disorder–reorder transition, with the \(\textit{x}\) = 0.08 composition exhibiting distinctive two-stage softening–hardening behavior. The established temperature–composition phase diagram enables systematic dielectric performance optimization, and the emergent metastable state at \(\textit{x}\) = 0.08 provides a critical structural guideline for designing high-performance lead-free ceramics for energy storage, sensing, and actuation applications.