Transport and dielectric properties of K doped glassy precursor for high TC superconductor showing ferroelectric behavior due to embedded nanocrystalline ferroelectric phase

Abstract

Partial substitution of Cu by K in multicomponent glassy precursor for high TC superconductor viz. Bi2−xPbxSr2Ca2Cu3Oδ (x=0.1–0.3) is found to destroy superconductivity of the corresponding annealed phase. These glasses viz. Bi2−xPbxSr2Ca2Cu3−yKyOz (x=0.1–0.3, y=0.2), however, show ferroelectric transitions (between 500 and 530 K depending on x). The corresponding K free glasses are not ferroelectric but they are good precursors for high TC superconductor. Nanocrystalline particles/clusters (∼10–50 nm size) embedded in the K doped glasses, observed from transmission electron microscopic studies, are considered to be responsible for the ferroelectric behavior of the bulk glass nanocrystal composite (GNC). Unlike K free glasses, the K-containing glasses do not become superconductor by annealing them at higher temperature. This indicates suppression of superconductivity by the precipitation of ferroelectric nanoparticles in the K doped GNC. Though their dielectric behavior is different, both the K free and K containing glassy systems are semiconductors and follow the similar nonadiabatic small polaron hopping conduction mechanism (obeying Holstein condition). A comparative study of the properties of the two glassy systems showing distinguishing behavior has been made.