Nd<SUB>2</SUB>Ba<SUB>2</SUB>CaCu<SUB>2&#8722;x</SUB>Zn<SUB>x</SUB>Ti<SUB>3</SUB> O<SUB>14</SUB>: a new family of tunable dielectric oxides showing a compositionally controlled tetragonal to cubic transition

Oxides of the formula Nd2Ba2CaCu2&#8722;xZnxTi3O 14 (x=0.0, 0.5, 1.0, 1.5, 2.0) have been successfully prepared by high temperature ceramic route at 1025 &#176;C, as well as by the low temperature citrate precursor route at 800 &#176;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) &#197; and c=19.63(1) &#197; for x=0, to a=3.925(1) &#197; and c=19.64(1) &#197; for x=1. The tetragonal distortion decreases with increase in zinc substitution and the oxides with x&#62;1.5 were found to crystallize in the cubic structure with a=3.933(2) and a=3.937(1) &#197; for the x=1.5 and two compositions, respectively. The entire range of oxides (0&#8804;x&#8804;2) could be obtained as pure phases at 800 &#176;C and crystallize in the cubic structure when prepared by the citrate precursor route. The room temperature dielectric constant (&#949;) 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 (&#949;) of 23 at 100 kHz when prepared by the citrate precursor method (&#949;=59, solid state route)