Structural evolution, dielectric, and energy storage properties of NaNbO3-Bi(Mg2/3Nb1/3O3)-NaMgF3 oxyfluorides

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.