Enhanced ferroelectric relaxation behaviors of KSr2Nb5O15-based ceramics by A-site entropy-engineering

•A novel tetragonal tungsten bronze structured ferroelectric ceramic was prepared.•The A-site entropy-engineering aggravated the distortion of NbO6 octahedrons.•Distortion of NbO6 octahedrons and grain size effects enhanced the relaxation features. A novel tetragonal tungsten bronze (TTB) structured K(Ca0.25Sr0.25Ba0.25La0.25)1.96Sm0.04Nb5O15 ferroelectric ceramic was prepared by an A-site entropy-engineering design. The results of Rietveld refinements of X-ray diffraction patterns showed that the A-site entropy-engineering aggravated the distortion of NbO6 octahedrons, especially along the single polarization axis direction. The aggravated distortion of NbO6 octahedrons and reducing of grain sizes further enhanced the ferroelectric relaxation feature, slightly strengthened the diffuseness degree, and caused the obvious frequency dependence of the dielectric phase transition around room temperature. This work provides a valuable strategy for tailoring the electric properties of tungsten bronze structured ferroelectric ceramics.