Nanocomposites and nanomaterials
Analysis of evolution of free volumes in the BaGa2O4 ceramics doped with Eu3+ ions
Klym H.1, Ingram A.2, Kostiv Yu.1, Luchechko A.1,3, Karbovnyk I.1,3
1 Lviv Polytechnic National University, Bandery str., 12, Lviv-79013, Ukraine 
E-mail: halyna.i.klym@lpnu.ua, klymha@yahoo.com
2 Opole University of Technology, Ozimska str., 75, Opole- 45370, Poland
3 Ivan Franko National University of Lviv,Tarnavskogo str., 107, Lviv-79017, Ukraine

The BaGa2O4 ceramics are considered as promising material for use as insulator in optoelectronic devices, as a secondary coating for plasma panels, etc. The doping of impurities in the form of rare-earth ions leads to the expansion of the functional properties of such ceramics. The goal of this work is to study the evolution of inner free volumes (extended defects and nanopores) in BaGa2O4 ceramics doped with different amounts of Eu3+ ions using positron annihilation lifetime spectroscopy (PAL) method.
The evolution of free-volume defects in the BaGa2O4 ceramics obtained by solid-phase synthesis from the initial BaCO3 and Ga2O3 components with the addition of different amount of Eu2O3 content (1, 3 and 4 mol%) were investigated. 
The ORTEC system with 22Na isotope as positron source were used for PAL measurements. Investigation were performed at 22 oC and relative humidity of 35 % for two identical ceramic samples placed in a sandwich configuration. The measured PAL spectra were calculated using LT software at four-component fitting procedure as for spinel ceramics with branched porous structure.
For the BaGa2O4 ceramics two PAL channels are possible: capture of positrons by bulk defects as well as channel of decay of ortho-positronium atoms. The short-term component reflects the microstructural features of the main phase, the middle one is connected with defect-related voids near grain boundaries and the lifetimes of the third and fourth long-term components are estimated the transformation of nanopores. Additional phases in ceramics are mainly localized near the grain boundaries and create defective centers for positron capture studied by PAL spectroscopy. Analyzing the second component of PAL spectra for the undoped and Eu3+-doped BaGa2O4 ceramics, it was shown that an increase of Eu3+ content from 1 to 3 mol% leads to agglomeration of free-volume defects near grain boundaries of ceramics. At the same time, nanopores in ceramics expand and their number increases. Further increase in the content of Eu3+ ions are accompanied with fragmentation of both free-volume defects and nanopores.