Dynamic Mechanical Analysis of Phase Transformations and Anelastic Relaxation in Stabilized Zirconias

Abstract

Elastic properties of polycrystalline stabilized zirconias, namely Yttria Stabilized Zirconia (YSZ) and Scandia, Ceria Stabilized Zirconia (SCSZ), were studied by Dynamic Mechanical Analyzer (DMA) in air. Changes of storage modulus E′, loss modulus E″ and mechanical damping (tanδ) with temperature were simultaneously monitored at various frequencies. In 8 mol% (8YSZ) and 10 mol% (10YSZ) Yttria Stabilized Zirconia, a drop in storage modulus of ∼37% was observed in the 30°C to 400°C temperature range, together with two frequency dependent damping peaks. While the first tanδ peak can be attributed to the anelastic relaxation of (Y′ZrVO••)• elastic (and dielectric) dipoles, the second one is probably the result of local ordering of oxygen vacancies and/or relaxation of (2Y′ZrVO••)x dipoles. For cubic SCSZ, four damping peaks were observed in the similar temperature regime accompanied by significant nonlinear drop of the storage modulus. The first tanδ is attributed to anealstic relaxation of (Sc′ZrVO••)•. It was also found that stress induced phase transformation from cubic to rhombohedral structure is the reason for the frequency dependent third peak in the tanδ spectra while the fourth frequency independent peak was found to be the result of the phase transformation from rhombohedral to cubic structure.