Structural evolution, dielectric, and energy storage properties of NaNbO ₃ ‐Bi(Mg _2/3 Nb _1/3 O ₃ )‐NaMgF ₃ oxyfluorides

Abstract We have prepared novel (1‐ x )[(1‐ y )NaNbO ₃ ‐yBi(Mg _2/3 Nb _1/3 O ₃ )]‐ x NaMgF ₃ (NN‐BMN‐NMF) ternary oxyfluoride solid solutions and investigated their structural, dielectric, electrical, and energy storage properties in this work. The single BMN‐doped solid solution experiences a transformation from the Pbma to the P2 ₁ ma phase. The NMF and BMN codoping further induce the pseudo‐cubic phase Pmmm, exhibiting the coexistence of the P2 ₁ ma and Pmmm phases. The MgO secondary phase appeared in the high‐level doped compositions. The single BMN or NMF‐doped composition demonstrates a homogeneous microstructure. However, the codoped ones exhibit a core‐shell fine‐grain microstructure. The NMF and or BMF doping decreases the polarizability of the solid solution. The single BMN‐doping or NMF and BMN‐codoping shifts the Tc toward much lower temperatures, accompanied by a broader permittivity maximum, than the same level of single NMF‐doping. The NMF ( x = 0.02) and BMN ( y = 0.10) codoped composition achieved optimized energy storage properties with recoverable energy density W _rec = 3.76 J/cm ³ , efficiency η = 80.7%, and breakdown strength ( E _b ) = 380 kV/cm.