Defects in Cubic Zirconia Studied by Mechanical Loss Spectroscopy

In cubic Y₂O₃ (10–25 mol%) or CaO (14 and 17 mol%) stabilized ZrO₂, oxygen vacancies are created as charge-compensating defects. Mechanical loss (internal friction) measurements are performed on single crystals of cubic zirconia with various orientation at frequencies of f ≈︁ 1 Hz and 1 kHz, to study the local crystallographic structure of the defects. The mechanical spectra show a composite loss maximum at 400–600 K consisting of two overlapping submaxima: I and I_A in ZrO₂-Y₂O₃; I' and I'_A in ZrO₂-CaO. Submaxima I (I') are assigned to defect pairs of oxygen vacancies and impurity atoms forming elastic (and electric) dipoles. These are oriented parallel to <111>, with the vacancy on nearest neighbour sites (trigonal symmetry). Submaxima I_A(I'_A) are attributed to relaxation of vacancies within Y- (or Ca-) clusters with various sizes and configurations corresponding to lower defect symmetry. The electrical conductivity (4 probe d.c. technique) decreases for concentrations ≥10mol% Y₂O₃, whereas the activation enthalpy increases with Y₂O₃ content. A high temperature peak C in ZrO₂-CaO around 1400 K (0.1 Hz) is probably due to local atomic jumps of cations.