Abstract
A lead-free BaTi0.975(Nb0.5Yb0.5)0.025O3 (BTYN25) ceramic sample was prepared using a solid state reaction method. The polymorphic phase transition (PPT) from the orthorhombic to the tetragonal phase (O-T) at room temperature (RT) was identified in this composition. An X-ray diffraction (XRD) study allowed the identification of those two structures at RT. Dielectric measurements made it possible to determine the phase transitions. The Raman study confirmed the structures and the phase transitions. A good piezoelectric coefficient of d33 = 140 pC/N, a planar electromechanical coupling factor of kp = 29% and a remanent polarization of Pr = 10.8 μC/cm2 were obtained. The electro-caloric effect (ECE) was investigated by using two different methods: an indirect method with hysteresis loops and a direct method with a modified Differential Scanning Calorimeter (DSC). A good electro-caloric strength (ξ = ΔT/ΔE) of ξ = 0.17 °C mm/kV near the ferroelectric-paraelectric phase transition temperature was obtained. At RT, a significant electro-caloric strength of ξ= 0.05 °C mm/kV was found due to the coexistence of the two phases: the orthorhombic one and the tetragonal one. A good agreement between the two methods was found. These values are very interesting when compared to those for other materials and show the possibility of using such lead-free ceramics for electro-caloric applications.
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