MECHANICAL LOSS MEASUREMENTS ON YTTRIA-STABILIZED AND CALCIA-STABILIZED ZIRCONIA

In cubic ZrO2 defects (oxygen vacancies) are created as a consequence of doping with lower valency cations (10 mol.% Y2O3 or 16 mol.% CaO) which are required for stabilization of the cubic phase. Mechanical loss measurements were applied on single crystals of cubic zirconia to study the local crystallographic structure of atomic defects. Specimens with different longitudinal axes ([100], [110], [111]) were measured in torsional (f approximate to 1 Hz) and flexural oscillations (f approximate to 1 kHz). A composite loss maximum consisting of two submaxima is observed: I (approximate to 410 K) and I-A (approximate to 510 K) in ZrO2-Y2O3; I'(approximate to 430 K) and I-A' (approximate to 515 K) in ZrO2-CaO (f approximate to 1 Hz). The peak heights of maxima I and I' depend on specimen orientation as expected for a defect of trigonal ([111]) symmetry. This strongly points to oxygen vacancies located at nearest neighbour sites close to the dopant atoms which form elastic (and electric) dipoles, i.e. (V-0*Y'(Zr))(.) or (V-0*Ca'')-pairs, which are aligned parallel to [111] directions. The anelastic shape factor of the dipoles characterizing the anisotropy and strength of the local atomic displacements was determined as delta lambda approximate to 0.1 for yttria-stabilized and delta lambda approximate to 0.05 for calcia-stabilized zirconia. Loss maxima I-A and I-A' are assigned to larger clusters of oxygen vacancies with two or more dopant atoms.