Nanocomposites and nanomaterials

Structural properties and free volumes in the Y-doped BaTiO3 ceramics
 H. Klym1, I. Karbovnyk1,2, Yu. Kostiv1 
1 Lviv Polytechnic National University, Bandery str., 12, Lviv-79013, Ukraine 
E-mail: halyna.i.klym@lpnu.ua, klymha@yahoo.com   
2 Ivan Franko National University of Lviv, Tarnavskogo str., 107, Lviv- 79017, Ukraine

In this work inner-structure properties in undoped and Y-doped BaTiO3 ceramics were studied using combined methods. BaTiO3 ceramics doped with 0.2, 0.4, 0.6 and 0.8 mol% of Y were sintered at 1250 oC. The positron annihilation lifetime (PAL) measurements were performed with an ORTEC spectrometer using 22Na source placed between two sandwiched ceramic samples. The obtained data were treated with LT computer program, the best results were obtained to two-component fitting procedures. 
In respect to SEM investigations, typical ceramic samples show grain-porous microstructure and assemblies of fractional grains. By accepting two-state positron trapping model, for polycrystalline ceramic materials the short lifetime of 10.16 ns is generally attributed to the free annihilation of positrons [1]. This value also correlated with theoretically calculated free positron lifetime in BaTiO3. The obtained value is closed to BaTiO3 single crystal. The presently observed values of 20.37 ns which is believed to come from the annihilation of positrons at vacancy complexes formed between the oxygen vacancies and the metal ion vacancies. It is shown that 2 decreases with rise of Y amount in BaTiO3 ceramics from 0.2 to 0.6 mol% and increases in samples with 0.8 mol% of Y the intensity I2 decreases from 20 to 15 %.
This indicates that doping of Y results in decreasing of the size of free-volume defects in ceramics and decreasing of their amount. So, process of so-called shrinking of defects is take place at posing of BaTiO3 ceramics by Y in amount of 0.4 and 0.6 mol%, while future increasing the Y content to 0.8 mol% leads to weakly expressed agglomeration of free-volume defects.

1.	Macchi C., Somo Macchi C., Somoza A., Dupasquier A., García A.L., and Castro M. Positron trapping in BaTiO3 perovskite // Journal of Physics: Condensed Matter. – 2001. - 13(24). – P. 5717.