Development of low cost (Sr,Ca)/sub 3/Al/sub 2/O/sub 6/ dielectrics for Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+/spl delta// applications

Aspects of the development of low-cost (Sr,Ca)/sub 3/Al/sub 2/O/sub 6/ dielectrics for Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+/spl delta// superconductor applications were investigated, A tie-line phase equilibrium relationship between Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+/spl delta// and Sr/sub 2/CaAl/sub 2/O/sub 6/ compositions was observed at 860/spl deg/C, When the Bi-2212 and (Sr,Ca)/sub 3/Al/sub 2/O/sub 6/ solid-solution compositions were changed slightly, the tie-line relationship was not preserved, and a new phase was observed to form with composition /spl sim/BiSr/sub 1.5/Ca/sub 0.5/Al/sub 2/O/sub x/. Composites of (0 to 24) volume fraction % Sr/sub 2/CaAl/sub 2/O/sub 6/-Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+/spl delta// equilibrated at 860/spl deg/C slightly reduced the T/sub c/ (by 2 K to 4 K) and superconducting volume percentage of the 2212 phase. The dielectric properties of (Sr=1.0 to 2.5) members of solid-solution (Sr,Ca)/sub 3/Al/sub 2/O/sub 6/ were measured at 77 K and 297 K in the range of (10 to 11) GHz for cylindrical samples using resonant system methods. The dielectric constant /spl epsiv//sub r/ varied from 9.7 to 13.2, and the loss tangent tan /spl delta/ was from 3/spl times/10/sup -4/ to 8/spl times/10/sup -4/.