Nanocomposites and nanomaterials

Variety of positron-electron annihilation kinetics in modified MgO–Al2O3 ceramics in the frequency domain
O. Ye. Fliunt1, H. Klym2, A. Ingram3
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.

As it was shown early in [1,2] positron-electron annihilation (PEA) kinetics in solids may be presented in the time or frequency domain. Frequency-domain response represents in-phase (real) and quadrature (imaginary) components of intensity of PEA annihilation in materials. Frequency spectra have some advantages in comparison with time-domain impulse characteristics that concern the possibilities of determining form of terms of relaxation. 
Spectra of PEA annihilation of modified (initial and after water treatment) MgO-Al2O3 ceramics have been calculated using integral Fourier transform. It is established that PEA spectra of modified MgO–Al2O3 ceramics show large maximum at frequency of 0.5-0.65 GHz that corresponds to characteristic relaxation time of 0.26–0.35 ns. At frequency of this maximum the most intensive interaction of modulated positron flux with ceramics takes place. After water treatment, some deviation of low-frequency side of large dispersion have been observed, allowing to consider large maximum as two components with much weaker lower frequency Debye type term. Water treatment leads also to increasing weak low-frequency component at frequencies of about 59–80 MHz showing significant spreading of maximum and deviation form Debye law [2]. Form variety of PEA spectra has been analyzed taking into account compatibility of spectra of real and imaginary components to integral Kramers-Kronig relations. 

1. Fliunt O., Klym H., Ingram, A. Multicomponent positron–electron annihilation kinetics in the MgO–Al2O3 ceramics in the frequency domain // Applied Nanoscience. – 2020. – P. 1-7. DOI:10.1007/s13204-020-01301-5
2. 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