Diffusion and electromigration of silver in PZT and HTSC ceramics

Abstract

Diffusion and electromigration of silver in ferroelectric ceramics of lead zirconate-titanate (PZT) PbZr_0.54Ti_0.46O₃ and diffusion of silver in high temperature superconducting (HTSC) ceramics YBa₂Cu₃O_7−x has been studied in air. The diffusion coefficient D in PZT varies from ≈ 10−¹⁰cm²/s at 370°C to ≈ 10⁻⁷ cm²/s at 700°C. The temperature dependence of D follows the relationship D = 0.19 exp (−1.21 eV/ kT) cm²/s. The electromigration of silver in PZT has been studied from 150 to 460°C in a constant electric field E = 700-1500 V/cm. Silver was found to migrate predominantly to the cathode. Above ≈ 400°C the regions of the local penetration of silver to the cathode were observed. The diffusion in HTSC has been studied in porous ceramics having a porosity varying from 17 to 34%. The silver concentration in a volume and the diffusion coefficient are found to increase with the porosity. In the range 500-800°C the diffusion coefficient D varies from ≈ 10⁻¹⁰ cm²/s to ≈ 10⁻⁷ cm²/s. The temperature dependence of D being represented by the expression D = 0.007 exp (−1.13 ev/kT) cm²/s (for the porosity 30-34%). The conclusion is made that in both PZT and HTSC ceramics silver migrates via the fast diffusivity paths—the pores and grain boundaries. The effect of gamma radiation on silver diffusion in HTSC ceramics has been studied in the range 370-500°C. The gamma radiation is found to stimulate the penetration of silver into the ceramics. In HTSC specimens which were over a long period of time (150-220 days) at room temperature the considerable silver diffusion was observed.

Key Words:

• PZT-
• HTSC-ceramics
• silver
• diffusion
• electromigration
• gamma-irradiation