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Lead-free barium calcium titanate zirconate (BCTZ) ceramics doped with a single rare-earth element generally exhibit excellent piezoelectric properties. However, their electrical properties deteriorate at an excessive dopant content, limiting their application. In this study, amphoteric neodymium (Nd3+) and yttrium (Y3+)-codoped BCTZ-NYx ceramics were synthesized via a solid-state reaction at 1240 °C. The influences of the Y3+ content (x) on the structural features, electrical properties, mechanical properties, and thermophysical properties were investigated. At a small x (<0.18 mol%), Y3+ could enhance the fracture strength and electrical properties by eliminating oxygen vacancies, defect dipoles, and/or structural defects. However, the outstanding performance deteriorated with excessive x. Additionally, the mechanism of the defect chemistry at different x was deduced. At an yttrium content of 0.18 mol%, the ceramic exhibited high piezoelectricity and ferroelectricity with low domain-switching activation energy (Ea = 0.401 eV), indicating that it could replace commercial lead-based piezoelectric ceramics. [ABSTRACT FROM AUTHOR]