Nanocomposites and nanomaterials

PALS models to estimate of free volume 
in ceramic materials with advanced nanoporosity
H. Klym1, A. Ingram2, I. Hadzaman3

1 Lviv Polytechnic National University, Bandery str., 12, Lviv-79013, Ukraine 
E-mail: halyna..klym@lpnu.ua; klymha@yahoo.com 
2Opole University of Technology, Ozimska str., 75, Opole- 45370, Poland
3 Drohobych State Pedagogical University,
I. Franko str., 24, Drohobych-82100, Ukraine
Progress in the modern nanomaterial’s science relies, to a great extent, on high-informative characterization probes sensitive to length scales of atomic and subatomic ranges. One of such probes is positron annihilation lifetime (PAL) spectroscopy, can be applied to study atomistic imperfections such as free-volume defects in different solids despite their structural organization. In this work PALS models were proposed to estimate of free volume in ceramic materials with advanced nanoporosity on example of MgAl2O4 ceramics. 
In ceramic materials with advanced porosity the model two channels of positron annihilation should be considered – the positron trapping and o-Ps decaying. In general, these processes are independent ones. However, if trapping sites will appear in a vicinity of grain boundaries near free-volume pores, they can become interconnected resulting in a significant complication of the measured PAL spectra. For humidity-sensitive MgAl2O4 ceramics the shortest (lifetime 1 and intensity I1) and middle (lifetime 2 and intensity I2) PAL components were ascribed to positron trapping modes. The longer 2 lifetime can be treated as defect-related one, these positron-trapping defects being located near grain-boundaries. The longest PAL component (lifetime 3) is attributed to ortho-positronium o-Ps decaying.
At high-statistical PAL measurements the spectra for ceramics can be described by two different channels related to positron trapping and o-Ps decaying (two long-lived components). The third and fourth components (3, I3) and (4, I4) originate from annihilation of o-Ps atoms in intrinsic nanopores of MgAl2O4 ceramics [1].

1.	Klym H., Ingram A., Shpotyuk O., Hadzaman I., Solntsev V. Water-vapor sorption processes in nanoporous MgO-Al2O3 ceramics: the PAL spectroscopy study // Nanoscale research letters, 2016, 11(1), pp.1-7.