K2SR4NB10O30-BASED DIELECTRIC MATERIALS E XHIBITING FLAT EPSILON(')(R)=F(T) CURVES WITH HIGH DIELECTRIC-CONSTANT

Type II ferroelectric ceramics are used in multilayers capacitors with high volume capacitance. Among different specifications concerning th e variation of the dielectric constant versus temperature, one of the most restrictive class, the X7R one, allows only a variation of +/-15 percent of the 25 degrees C value of the permittivity in the wide rang e, -55 degrees C to +125 degrees C. Previous investigations have prove d the interest to mix the niobate K2Sr4Nb10O30, with a Tetragonal Tung sten Bronze (TTB) structure, with perovskites as minor agents like Pb( Mp(1/3)Nb(2/3))O-3, to obtain flat curves epsilon(r)' = f(T) with diel ectric constant above 6000. To point out the mechanism leading to such curves, the influence of the introduction of different cations like M g2+ or Pb2+ in the TTB structure has been studied. In the present work , we show that K2Sr4Nb10O30-based materials, without the presence of p erovskite phase from XRD, can also exhibit epsilon(r)' = f(T) curves w ith a flat profile.