Applied Surface Science 426 (2017) 386–390 Contents lists available at ScienceDirect Applied Surface Science journal h om epa ge: www.elsevier.com/locate/apsusc Full Length Article Raman, EPR and ethanol sensing properties of oxygen-Vacancies SrTiO 3- ı compounds H. Trabelsi a,∗ , M. Bejar a , E. Dhahri a , M.P.F. Grac ¸ a b , M.A. Valente b , M.J. Soares b , N.A. Sobolev b a Laboratoire de Physique Appliquée, Faculté des Sciences, B.P. 1171, 3000 Sfax, Université de Sfax , Tunisia b I3N and Physics Department, University of Aveiro, 3810-193 Aveiro, Portugal a r t i c l e i n f o Article history: Received 1 February 2017 Received in revised form 17 June 2017 Accepted 16 July 2017 Available online 19 July 2017 Keywords: SrTiO3 Oxygen vacancies Raman EPR Gas-sensor a b s t r a c t Polycrystalline SrTiO 3- ı powders with cubic perovskite phase were prepared by solid-state reaction method followed by the creation of oxygen vacancies ı-thermal activated. The Raman spectroscopic investigation was carried out in a frequency range of 100–2000 cm -1 , and the second-order Raman modes were observed at room temperature. The Electron Paramagnetic Resonance (EPR) results revealed that SrTiO 3- ı samples had evident EPR signals that increased significantly with oxygen-vacancy concentra- tions. The incorporation of oxygen vacancies was found to decrease the thermal resistivity. Besides, the electrical sensing measurements showed that sensors based on SrTiO 2.925 (STO1) and SrTiO 2.875 (STO2) exhibited semiconductor behavior, while SrTiO 2.75 -based sensor (STO3) revealed the introduction of a metallic behavior at low temperature. Furthermore, these measurements confirmed that the resistivity increased after the introduction of the ethanol gas, which indicates that our samples can be considered as sensors for ethanol gas detection. The formation of oxygen vacancies under ethanol exposure at the surface of SrTiO 3- ı sensors was evaluated by photoluminescence. © 2017 Elsevier B.V. All rights reserved. 1. Introduction Gas sensor is an extensively used material in the field of gas detection, among which ethanol, a hypnotic gas with a toxic nature, has been widely investigated thanks to its various and practical applications [1]. Many research works have reported that semi- conducting materials is broadly used for the ethanol gas sensors [2,3]. The strontium titanate (SrTiO 3 ) material is semiconducting oxide sensing material that has been well studied for gas sensors. It has the advantages of being low cost and stable in both thermal and chemical atmospheres [4,5]. For the bulk conducting type of this material, the carriers require a high enough energy to overcome the Schottky barriers at the grain boundary [5–7]. On the other hand, oxygen deficiency is one of the most impor- tant modifying factors, which has to be taken into account for all oxide materials. Oxygen vacancies in SrTiO 3 are known to dope the material with electron carriers, which cause the change of opti- cal and electrical properties [8]. Recently, Wenfei Xu et al. have stated that there exist additional energy levels in the band gap, ∗ Corresponding author. E-mail address: hamdi.trabelsi@outlook.fr (H. Trabelsi). which contribute to the red shift in blue luminescence region [9]. The stability of the oxygen vacancy complex in SrTiO 3 has been thoroughly studied using in-situ electron paramagnetic resonance (EPR)/annealing measurements at different temperatures [10]. The change in the concentration of the oxygen vacancy makes the sys- tem change from insulator to semiconductor, and to metallic (and superconducting) behavior [11]. Besides, oxygen vacancies could make SrTiO 3- ı compounds sensitive to reducing gas. The present work aims to study the Raman, RPE and electric resistivity of SrTiO 3- compounds at different temperatures over a wide range of ethanol vapor concentrations. A comparison of the Photoluminescence (PL) spectra before and after electrical sensing measurements was also reported. 2. Experimental details The SrTiO 3 parent compound was prepared by the conventional solid-state reaction. Stoïchiometric SrCO 3 and TiO 2 powders were mixed and then calcined at 800 ◦ C for 12 h. The obtained powder was pressed into pellet forms and sin- tered at 1100 ◦ C and then to 1300 ◦ C under oxygen atmosphere with several periods of grinding and repelling. In order to create vacancies in oxygen sites, the SrTiO 3 parent compound was placed http://dx.doi.org/10.1016/j.apsusc.2017.07.128 0169-4332/© 2017 Elsevier B.V. All rights reserved.