Abstract
The influence of La3+-doping on the electrocaloric effect (ECE) of the 0.75(Pb1-3x/2Lax)(Mg1/3Nb2/3)O3-0.25(Pb1-3x/2Lax)TiO3 (L-PMN-PT: x/75/25 x = 0.0–4.0 mol.%) ceramics was studied. With the increase of La3+-doping in these ceramics, the relaxor ferroelectric properties increase, while the average grain size, coercive field Ec and Curie temperature TC decrease. As a result, a maximum adiabatic temperature change ΔT as high as 0.68 K, measured by direct measurement method, was achieved under a lower electric field (E) intensity of 5 kV/mm at 383 K for samples with x = 2.0 mol.%. Besides the high ΔT value, the La3+-doping also leads to a temperature insensitivity of ΔT. The variation of ΔT is less than 0.15 K, or 28.3%, over a wide temperature range of 303–423 K. The La3+-doped PMN-PT ceramics, with large and temperature insensitive ΔT over a broad temperature range, is very helpful for practical application. The reduction of Ec and TC can be attributed to the suppression of long-range coupling between oxygen octahedrons due to the partial replacement of Pb2+ by La3+. The temperature insensitivity of ECE is attributed to the enhancement of relaxor ferroelectric properties.
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