Nanoscale physics

The humidity sensitivity of magnesium-zinc gallate solid solutions with spinel structure
O. Kravets1, O. Zaremba1, Ya. Shpotyuk1,2, A. Luchechko1, 
K. Szmuc2, J. Cebulski2, A. Ingram3, O. Shpotyuk4,5
1 Ivan Franko National University of Lviv, Universytetska Str., 1, Lviv 79000, Ukraine. E-mail: oleg.kravets92@gmail.com
2 University of Rzeszow, Rzeszow, 35-959, Poland.
3 Opole University of Technology, 75, Ozimska str., 45370, Opole, Poland
4 Jan Dlugosz University, al. Armii Krajowej, 13/15, 42201, Czestochowa, Poland
5 Vlokh Institute of Physical Optics, 23, Dragomanov str., 79005, Lviv, Ukraine

The oxide ceramic materials have become a high spot on the topic of humidity sensing due to several advantages, in particular, chemical stability, fast response and high sensitivity [1]. Recently, gallate spinel compounds showed good biocompatibility and possibility to be applied as gas sensitive media [2]. Moreover, MgGa2O4 and ZnGa2O4 spinels show efficient emission in a broad spectral range depending on used activator ions [2].
The Mg1-xZnxGa2O4 (x= 0-1.0) solid solutions were synthesized via high-temperature solid-state technique. The ceramic samples were characterized with X-ray diffractometry, transmission electron microscopy, positron annihilation lifetime spectroscopy. The luminescent properties and electrical conductivity were studied at different humidity.
The XRD analysis confirmed formation of spinel phase in all samples. The TEM and STEM diffraction showed formation of ceramic samples with a broad size distribution of crystallites. The PALS measurements exhibited a high-intensity maximum with a characteristic decay time of water contained voids. Investigation of the luminescence spectra showed the changes of the total and relative intensity of emission bands at different humidity. The electrical conductivity measurements showed changes of the complex resistance of the samples at different frequencies of the applied voltage. 

1.	Divya T., Nikhila M.P., Anju M. et al. Nanoceria based thin films as efficient humidity sensors // Sensors and Actuators A: Physical -2017.-261.-P. 85-93.
2.	Luchechko A., Kravets O. Novel visible phosphors based on MgGa2O4-ZnGa2O4 solid solutions with spinel structure co-doped with Mn2+ and Eu3+ ions // J. Lumin.-2017.-192.-P. 11-16.