Oxygen vacancy trapping in tetragonal ZrO2 studied by 111In/Cd perturbed angular correlation

Perturbed angular correlation (PAC) spectroscopy using dilute In-111/Cd as the probe atom was used to measure the average electric field gradient (EFG) at Cd in high-temperature tetragonal zirconia, both nondoped and lightly doped with niobium or yttrium. The time-average EFG is reduced and strongly temperature dependent when oxygen vacancies are present-an effect attributed to a reduction of the average EFG when a vacancy is trapped at Cd. The doping and temperature dependence of the average EFG indicate that oxygen vacancies are trapped at first-neighbor positions to Cd with binding energy 0.62 (3) eV and at second neighbor positions to Y with binding energy 0.28 (5) eV. The average EFG when a vacancy is trapped by Cd is found to be zero. Samples were produced by precipitation from ZrOCl2 solutions to which a few parts per 10(9) (InCl)-In-111 was added. Y- or Nb-doped samples had Y/Zr or Nb/Zr ratios up to 0.005. Calcining at 800 degrees C followed by a 1400 degrees C anneal produced good quality tetragonal phase powders with oxygen vacancy to oxygen ion ratios between 0 and 1500 ppm, depending on doping. The tetragonal phase could be supercooled for measurement to 1000 degrees C or lower.