Abstrakt
Positron annihilation spectroscopy was employed for investigation of vacancy-like defects in plasma-sprayed barium titanate. Defect studies were combined with measurement of dielectric properties of barium titanate coatings.
Samples prepared by gas-stabilized plasma spray (GSP) torch and by plasma torch with the hybrid water-argon stabilization (WSP-H) were studied. Processing parameters were selected so that GSP coatings were sprayed in reductive conditions, whereas WSP-H coatings were prepared in oxidizing environment.
As-sprayed GSP coating is dark, whereas WSP-H one is light. The dielectric properties of WSP-H coating are superior to those for GSP one.
Defect studies revealed that both GSP and WSP-H coatings contain titanium vacancies. However, GSP coating contains in addition a considerable concentration of oxygen vacancies.
Some fraction of oxygen vacancies in GSP coating is coupled with titanium vacancies forming partial Schottky defect. The structure of WSP-H coating is less disordered and contains only a low concentration of oxygen vacancies.
This is consistent with reductive and oxidizing conditions in GSP and WSP-H spraying, respectively. Annealing at elevated temperatures in air leads to removal of oxygen vacancies which are filled by oxygen diffusing into the samples.