Nanocomposites and nanomaterials

Water-adsorption processes on the modified MgO-Al2O3 ceramics studied in the frequency domain

O. Ye. Fl’unt1, H. Klym2, A. Ingram3, R Szatanik3
1 Department of Electronics and Computer Technology, Ivan Franko National University of Lviv, Dragomanov Str., 50, Lviv-79005, Ukraine. 
2 Lviv Polytechnic National University, Bandery Str., 12, Lviv-79013, Ukraine.
E-mail: halyna.i.klym@lpnu.ua; klymha@yahoo.com 
3 Opole University of Technology, Ozimska Str., 75, Opole- 45370, Poland.

Positron-electron annihilation (PEA) kinetics in the modified MgO-Al2O3 ceramics sintered at different temperatures and durations with following water adsorption procedure has been calculated and analyzed in the frequency domain [1,2]. The spectra of real (in-phase) and imaginary (quadrature) components of modulated positron-electron annihilation response have been obtained numerically from temporal kinetic characteristics using integral Fourier transform. 
In is shown that the obtained complex spectra of PEA in the MgO-Al2O3 ceramics in the frequency domain obey a sum of two Debye law components denying correlation between elementary positron annihilation processes. Strong increasing of amplitude of lower frequency Debye component caused by water adsorption on the frequency spectra has been observed. Characteristic frequencies of Debye type components of water immersed samples show weaker dependencies on sintering temperature than in just sintered ones. 
It is established that position of maxima of the large relaxation process of water adsorbed ceramics on frequency dependence of modulated PEA corresponds to average relaxation time of the two fastest components derived from the impulse time-domain kinetic response. Within the frame of this conception the physical meaning of the fastest average time is a reverse value of the modulation frequency on which the most effective interaction of positrons flux with electrons localized on the fastest traps in material takes place. 

1. Fl’unt O., Klym H., Ingram A., Szatanik R. Effect of water adsorption on positron–electron annihilation kinetics in the MgO–Al2O3 ceramics in the frequency domain // Applied Nanoscience. – 2019. – P. 1-6. 
DOI: 10.1007/s13204-019-01040-2