High-performance Pb(Zr_1−xTi_x)O₃ (PZT) piezoceramics are urgently desired by the market in view of their expanded operating temperature range, reduced property temperature dependence, and enhanced sensitivity and acoustic power. In this work, we reported a kind of low-cost and high-performance 0.06BiYbO₃–0.94Pb(Zr_0.48Ti_0.52)O₃ ternary piezoceramics; the modifying effects of La₂O₃ on this perovskite system were investigated in terms of the structures, electrical properties, and thermal depolarization behaviors of ceramics. The field-dependent dielectric and conduction properties indicated that there are close correlations among oxygen vacancies (V_O), conducting electrons, and intrinsic conduction process. The degradation in ferroelectric properties observed in those samples doped with more than 0.15 wt% of La₂O₃ indicated that the occupying mechanisms of La³⁺ changed from the donor substitution for Pb²⁺ to the isovalent substitution for Bi³⁺. The thermally depoling micromechanisms of ceramics were revealed from the thermodynamic processes of defect dipoles and intrinsic dipoles within ferroelectric domains. The sample doped with 0.15 wt% of La₂O₃ shows excellent electrical properties with T_C = 387 ℃, d₃₃ = 332 pC/N, TK_ε = 5.81×10⁻³ ℃⁻¹, P_r = 20.66 μC/cm², T_d = 356 ℃. The significantly enhanced electrical properties and thermal depolarization temperature benefited from the donor substitution of La³⁺, decreasing the oxygen vacancy concentration in the lattice and possibly optimizing the ferroelectric domain structure of ceramics.