Nanocomposites and nanomaterials

Analysis of structural properties of Ca-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 Ca-doped BaTiO3 ceramics were studied using combined methods. Undoped BaTiO3 ceramics and doped with 5, 10 and 15 mol% of Ca 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 10.15 ns is generally attributed to the free annihilation of positrons. This value also correlated with theoretically calculated free positron lifetime in BaTiO3. The obtained value is closed to BaTiO3 single crystal. The second lifetime 2 arises from annihilation of positrons at defect sites. The presently observed values of 20.32 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 increases with rise of Ca amount in BaTiO3 ceramics from 5 to 10 mol% and decreases in samples with 15 mol% of Ca the intensity I2 decreases from 22 to 16 % and increases to 25 % in samples with 15 mol% of Ca.
This indicates that doping of Ca results in increasing of the size of free-volume defects in ceramics and decreasing of their amount. So, process of agglomeration of defects is take place at posing of BaTiO3 ceramics By Ca in amount of 5 and 10 mol%, while future increasing the Ca content to 15 mol% leads to fragmentation 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.