Electrical properties and high figure-of-merit of dielectric tunable (1-x)Ba(Zr_0.25Ti_0.75)O₃-xMgO thick films prepared by tape-casting

(1-x)Ba(Zr_0.25Ti_0.75)O₃-xMgO (x = 0.0, 0.1, 0.2, 0.3, 0.4) thick films were prepared by using a solid state reaction and tape-casting method. It is found that Mg not only exists in the MgO but also in the Ba(Zr_0.25Ti_0.75)O₃ detected by X-ray diffraction, field-emission scanning electron microscopy, transition electron microscopy and energy dispersive spectrum. With the increase of MgO content, the Curie temperature of thick films shifts from room temperature (283 K) of x = 0.0 to lower temperature (153 - 173 K). The dielectric relaxation properties of thick films were described by a Lorentz relation and the dc bias electric field dependences of the dielectric permittivity were described by a Johnson's phenomenological equation based on Devonshire's theory. The dielectric tunability, loss angle tangent and figure-of-merit of x = 0.4 at room temperature and 42 kV/cm were 30.56%, 0.00139 and 219.86, respectively.