Nd 2Ba 2CaCu 2− xZn xTi 3O 14: a new family of tunable dielectric oxides showing a compositionally controlled tetragonal to cubic transition

Abstract

Oxides of the formula Nd 2Ba 2CaCu 2− x Zn x Ti 3O 14 ( x=0.0, 0.5, 1.0, 1.5, 2.0) have been successfully prepared by high temperature ceramic route at 1025 °C, as well as by the low temperature citrate precursor route at 800 °C. The copper-rich compounds obtained by the ceramic route ( x=0–1.0) are found to have a tetragonal structure, with the a and c parameters increasing with zinc substitution, from a=3.913(8) Å and c=19.63(1) Å for x=0, to a=3.925(1) Å and c=19.64(1) Å for x=1. The tetragonal distortion decreases with increase in zinc substitution and the oxides with x>1.5 were found to crystallize in the cubic structure with a=3.933(2) and a=3.937(1) Å for the x=1.5 and two compositions, respectively. The entire range of oxides (0≤ x≤2) could be obtained as pure phases at 800 °C and crystallize in the cubic structure when prepared by the citrate precursor route. The room temperature dielectric constant ( ε) at 100 kHz varies from 8 for the pure Cu composition and increased to 59 for the pure Zn analog. The dielectric constant depends on the synthetic route—the pure Zn compound Nd 2Ba 2CaZn 2Ti 3O 14 gave much lower dielectric constant ( ε) of 23 at 100 kHz when prepared by the citrate precursor method ( ε=59, solid state route).