| Electrocaloric effect (ECE) is defined as the reversible adiabatic temperature change of the dielectric materials upon the application or removal of an external electric field, it has a great potential in realizing environmentally friendly solid-state cooling devices with compact size and high energy efficiency. Although high ECE can be achieved in the thin film and copolymer by apply high electric field, they are not suitable for the practical application. So, high electrocaloric strength, △T/△E, is desired for the application of electrocaloric effect. Bulk oxide materials have high electrocaloric strength, and compared with singly crystal, ceramics have the merits of low cost, so the ECEs of ceramics are focused in the present work. BaTiO3 ceramics is a typical lead-free ferroelectric, and its Cuire temperature can be easily tuned by the substitution. In this thesis, the dielectric properties, ferroelectric properties and ECE of Ba(Ti1-xSnx)O3 (x=0.1,0.15 and 0.175) and Ba(Ti1-xCex)O3 (x=0.1,0.15 and 0.2) ceramics were investigated.Ba(Ti1-xSnx)O3 (x=0.1,0.15 and 0.175) ceramics prepared by the spark plasma sintering (SPS) process were dense and fine-grained. Their dielectric properties, ferroelectric properties and ECE were determined. The best ECE was achieved in Ba(Ti0.85Sn0.5)O3 ceramic, and the highest EC temperature change (△T) of 1.17 K, entropy change (△S) of 8.38 J/kg·K and EC strength (△T/△E) of 0.098×10-6 K·m/V were obtained under the electric field of 120 kV/cm at 303 K.Ba(Ti1-xCex)O3 (x= 0.1,0.15 and 0.2) ceramics were prepared by a standard solid-state sintering method. The dielectric properties, ferroelectric properties and ECE of Ba(Ti1-xCex)O3 ceramics were investigated. Among there ceramics, Ba(Ti0.9Ce0.1)O3 ceramic has the best ECE properties.. the highest EC temperature change (△T) of 0.48 K, entropy change (△S) of 3.64 J/kg·K and EC strength (△T/△E) of 0.12×10-6 K·m/V were obtained under the electric field of 40 kV/cm at 403 K. |
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