Regular Article Effect of MCl (M = Na, K) addition on microstructure and electrical conductivity of forsterite ★ Saloua El Asri 1,2,* , Hamid Ahamdane 1 , Lahoucine Hajji 2 , Mohamed El Hadri 1 , Moulay Ahmed El Idrissi Raghni 1 , and Mohammed Mansori 2 1 Laboratory of Materials Science, Faculty of Sciences Semlalia, B.P. 2390 Marrakech, Morocco 2 Laboratory of Innovative Materials, Energy and Sustainable Development (IMED-Lab), Faculty of Sciences and Technology, Marrakech, Morocco Received: 1 June 2020 / Received in final form: 20 August 2020 / Accepted: 24 August 2020 Abstract. Forsterite single phase powder Mg 2 SiO 4 was synthesized by sol–gel method alongside with heat treatment, using two different cation alkaline salts MCl as mineralizers (M = Na, K) with various mass percentages (2.5, 5, 7.5, and 10 wt.%). In this work, we report on the effect of the cation type and the added amount of used mineralizer on microstructure and electrical conductivity of Mg 2 SiO 4 . The formation of forsterite started at 680–740 °C and at 630–700 °C with KCl and NaCl respectively, as shown by TG-DTA and confirmed by XRD. Furthermore, the Fourier transform infrared (FTIR) transmission spectra indicated bands corresponding to vibrations of forsterite structure. The morphology and elemental composition of sintered ceramics were examined by SEM-EDX analyses, while their densities, which were measured by Archimedes method, increased with addition of both alkaline salts. The electrical measurements were performed by Complex Impedance Spectroscopy. The results showed that electrical conductivity increased with the addition of both mineralizers, which was higher for samples prepared with NaCl than those prepared with KCl. 1 Introduction In recent years, olivine materials including forsterite Mg 2 SiO 4 and Co, Mn and Fe-doped forsterite (eg, MgCoSiO 4 , MgMnSiO 4 and MgFeSiO 4 ) are of particular interest to researchers due to their promising potential use as materials for energy storage applications, namely solid oxide fuel cells SOFCS and cathode for Mg-ion recharge- able batteries [1–5]. This potential use was highlighted due to some required characteristics, namely safety, because pure Mg has a high melting point (650 °C), compared to lithium (180 °C), and strong Si–O bond of polyanion SiO 4 , which makes forsterite structure stable to be used in high- temperature large scale. Furthermore, the constituent elements are non-toxic and abundant, and that make it inexpensive [6]. However, the difficulty of intercalation- desinterlaction of Mg ion in olivine structure and low ionic conductivity of Mg 2 SiO 4 make the achievement of theoretical capacity (300 mmap · h) very difficult [4]. Forsterite structure consists of a distorted hexagonal arrangement formed by polyhedron of Si–O where Si is located in tetrahedral site surrounded by O that in turn forms two non-equivalent octahedral sites M 1 and M 2 occupied by Mg ions. The existence of point defects in forsterite structure leads to conducting the electrical conduction via ionic diffusion mainly at high temperature. The common known point defects are M vacancies (M = Mg, O), that consists of jumping from one site to a neighboring vacant site, and interstitial defects such as Frenkel defect type, that consists of moving Mg ion from site to an interstitial site [7]. According to the literature, the mean responsible predicted defect of the electrical conduction in forsterite is Mg vacancies defect, particularly the hopping of Mg from M1 to M1 site [8]. In order to enhance its ionic conductivity, previous works were focused on studying the effect of microstruc- ture, doping element and thermodynamic conditions on the electrical conductivity of Mg 2 SiO 4 [9–11]. Synthesis of Forsterite Mg 2 SiO 4 by solid-state reaction is very difficult. In fact, a heat treatment up to 1200–1600 °C is necessary to obtain single phase forsterite [12,13]. This is overcomed by using mineralizers to accelerate the diffusion of the raw materials [14]. We have recently reported about the potential use of forsterite as ceramic pigments. The latter was synthesized by a sol gel route with using (H 2 Si 2 O 5 )aq as Si precursor and alkaline salts (KCl and NaCl) as mineralizers [15]. The aim of this research is to explore the effect of these mineralizers on microstructure and electrical conductivity of forstertite. For this purpose, both alkaline salts were added at different mass percents (0%, 2.5%, 5%, 7.5%, and 10%) and obtained samples were then investigated by thermal, chemical, microstructure and electrical conduc- tivity characterizations. ★ Contribution to the Topical Issue “Advanced Materials for Energy Harvesting, Storage, Sensing and Environmental Engi- neering (ICOME 2019)”, edited by Mohammed El Ganaoui, Mohamed El Jouad, Rachid Bennacer, Jean-Michel Nunzi. * e-mail: saloua.el.asrii@gmail.com Eur. Phys. J. Appl. Phys. 92, 10901 (2020) © EDP Sciences, 2020 https://doi.org/10.1051/epjap/2020200161 THE EUROPEAN PHYSICAL JOURNAL APPLIED PHYSICS 10901-p1