Dual-peak electrocaloric effect (ECE) exists over a broad range significantly below Curie temperature in co-mixed SrBi1.98La0.02Nb2–xTaxO9 (SBLNT) compositions exhibiting diffused phase transition. The indirect measurement method is used to study the influence of defect-modified potential barrier distributions on the ECE of lead-free SBLNT ceramics. Variation in isothermal entropy change and adiabatic temperature change with varying tantalum (Ta) content signify effects of morphology and impact of altered potential barriers in the parent lattice without involving structural phase transition. A unique appearance of twin-peak positive–negative ECE in equally doped SrBi1.98La0.02Nb-TaO9 matrix is attributed to doping-induced formation of polar nanoregions and distinct dipole switching mechanisms controlled by evenly distributed Nb–Ta potential barriers in SBLNT lattice. Higher doping concentration reduces porosity and promotes electric polarization, thereby the relative cooling power gradually increases with increasing Ta at Nb sites. © 2021 Wiley-VCH GmbH