Enhancing Energy Storage Performance in Lead-Free Bismuth Sodium Niobate-Based Tungsten Bronze Ceramics through Relaxor Tuning.

A series of tungsten bronze Sr 2 Na 0.85 Bi 0.05 Nb 5- x Ta x O 15 (SBNN- x Ta) ferroelectric ceramics were designed and synthesized by the traditional solid-phase reaction method. The B-site engineering strategy was utilized to induce structural distortion, order-disorder distribution, and polarization modulation to enhance relaxor behavior. Through investigating the impact of B-site Ta replacement on the structure, relaxor behavior, and energy storage performance, this study has shed light on the two main factors for relaxor nature: (1) with the increase of Ta substitution, the tungsten bronze crystal distortion and expansion induced the structural change from an orthorhombic Im 2 a phase to Bbm 2 phase at room temperature; (2) the transition from ferroelectric to relaxor behavior could be attributed to the coordinate incommensurate local superstructural modulations and the generation of nanodomain structure regions. Moreover, we benefited from the effective decrease of ceramic grains and inhibition of abnormal growth. Finally, we obtained an effective energy storage density ( W rec ) ∼ 1.6 J/cm 3 , an efficiency (η) ∼ 80%, a current density ( C D ) ∼ 1384.2 A/cm 2 , and a power density ( P D ) ∼ 138.4 MW/cm 3 .