Abstract: Electrocaloric cooling offers a promising route to solid-state refrigeration, but combining a large adiabatic temperature change with a broad working temperature range under moderate electric fields remains challenging in ceramic materials. This study investigates the effects of Sm content on the structure, dielectric behavior and electrocaloric performance of 0.9PST-0.1PT ceramics, with the aim of improving the trade-off between temperature change and operating temperature span. Pb_1-xSm_x(Sc_0.45Ta_0.45Ti_0.1)O₃ ceramics with x = 0.005, 0.01, 0.02 and 0.03 were prepared by the conventional solid-state reaction method. X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and domain characterization were combined with dielectric and polarization measurements. The electrocaloric responses were evaluated using the Maxwell relation and direct calorimetry. With increasing Sm content, the grains became finer, the rhombohedral phase fraction decreased, the dielectric diffuseness exponent increased from 1.56 to 1.85, and the peak permittivity temperature shifted from 32 to −11 ℃. Minor pyrochlore-related reflections appeared at x ≥ 0.02. Calculations based on a unified temperature range and the descending branch of the positive-field P-E loops gave peak adiabatic temperature changes of 2.34, 2.48, 2.09 and 1.58 K for x = 0.005, 0.01, 0.02 and 0.03, respectively, at a common field of 100 kV/cm. For x = 0.01, the temperature interval over which ΔT remained at or above 80% of its peak value spanned at least 98.43 K within the measured range. This composition exhibited an indirectly determined peak temperature change of 2.92 K at 120 kV/cm and a directly measured value of 2.15 K at 303 K under the same field. Structural, dielectric and domain observations support the interpretation that moderate Sm substitution modifies the local polarization environment and broadens the temperature-dependent polarization response, whereas secondary-phase formation at higher Sm contents is accompanied by reduced temperature changes at the common field. The x = 0.01 composition combines a relatively large temperature change with broad temperature coverage, thus providing a basis for optimizing PST-PT electrocaloric ceramics.

Key words: electrocaloric effect, lead scandium tantalate, donor doping, relaxor ferroelectric