Nd₂Ba₂CaCu_2−xZn_xTi₃ O₁₄: a new family of tunable dielectric oxides showing a compositionally controlled tetragonal to cubic transition

Abstract

Oxides of the formula Nd₂Ba₂CaCu_2−xZn_xTi₃O 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 Nd₂Ba₂CaZn₂Ti₃O₁₄ gave much lower dielectric constant (ε) of 23 at 100 kHz when prepared by the citrate precursor method (ε=59, solid state route).