Nanocrystalline Li 2 MoO 4 : Synthesis and electrical studies Rajesh Cheruku a, b , D. Surya Bhaskaram a , G. Govindaraj a, * , Lakshmi Vijayan c a Department of Physics, School of Physical, Chemical and Applied Sciences, Pondicherry University, R.V. Nagar, Kalapet, Pondicherry, 605 014, India b School of Chemical Engineering, Yeungnam University, 214-1, Dae-dong, Gyeongsan-si, Gyeongsangbuk-do, 712-749, Republic of Korea c St. Aloysius' College, Edathua, Alappuzha, Kerala, 689 573, India article info Article history: Received 19 December 2018 Accepted 23 February 2019 Available online 27 February 2019 Keywords: Chemical synthesis Nanocrystalline Electrical properties Pinned and free dipole abstract Li-Mo-O phase class materials are suitable negative electrode materials for Li-ion batteries. They exhibit better performance at the nanoscale level. This current work deals with the synthesis of nanocrystalline Li 2 MoO 4 material, synthesized by the solution combustion technique using citric acid as the chelating agent. X-ray diffraction and electron microscopy with energy dispersive X-ray analysis were employed to study the structure and morphology of the prepared material. Fourier transform infrared spectroscopy was utilized to study the molecular structure and chemical bonds present in the material. Magnetic characteristics of the Li 2 MoO 4 were explored using the vibrational sample magnetometer. Frequency-and temperature-dependent electrical properties were explored using broadband dielectric spectroscopy. The results revealed the presence of two different relaxations, one corresponding to the free dipoles of LiO 4 and MoO 4 molecules and the other corresponding to the relaxation of pinned dipoles formed by the association of free carriers with defects. A novel model combining these relaxations was used to fit the electrical data. Activation energies for relaxation and DC conduction were calculated, and the corre- sponding results were discussed. © 2019 Elsevier B.V. All rights reserved. 1. Introduction Currently, the rapid growth of new technologies, such as hybrid electric automobiles and compact electronic devices, has resulted in increasing demand for batteries with a high power capability and energy density. If the majority of gasoline-utilized transportation is substituted by electric vehicles, greenhouse gas emission will considerably decrease. In this regard, Li-ion batteries are one of the best batteries commercially available for use in electric vehicles because of their high energy density, high power density, and low weight [1e5]. Hence, the research community has focused on developing the best materials for Li-ion battery components, namely, the anode (negative electrode), cathode (positive elec- trode), and electrolyte. For commercial Li-ion cells, graphite is extensively used as the dominant negative electrode, but it has a relatively low specific capacity (372 mAh/g). Additionally, the Li-ion intercalation/ extraction smitten with graphite occurs at low potential, to raise safety issues [6]. Thus, graphite needs to be replaced with other anode materials that are better in terms of energy density, power density, good cycle liability, and safety. In fact, transition metal oxides are considered good competitive material for Li-ion battery anodes, because they exhibit a higher potential than Li þ /Li in graphite, low cost, high reversible capacities, and environmental safety [7,8]. Specifically, molybdenum-based oxides and a chain of molybdates, such as MMoO 4 (M ¼ Mn, Cu, Zn, Ni, Fe, Ca) [9e11], have been studied extensively regarding their electrochemical in- tercalations of lithium as a potential negative electrode for Li-ion batteries. Recently, the Li-Mo-O phase class, consisting of Li 2 MoO 4 [12], Li 4 Mo 3 O 8 , and LiMoO 2 [13], has been utilized as negative electrode material for Li-ion batteries. Nevertheless, the rate capability and cycle performance of these molybdates need improvement. This improvement can be achieved by reducing the size of these mate- rials to the nanoscale. Until now, different methods were used to synthesize Li 2 MoO 4 , including the sol-gel method [14], thermal polymerization method [12], aqueous solution method [15], and hydrothermal treatment [16]. In the current study, Li 2 MoO 4 was prepared by the solution combustion method. Numerous researchers anticipated that the solution combustion method is a powerful technique and easy route for preparing the materials at the nanoscale level with high * Corresponding author. E-mail address: chraj.25@gmail.com (R. Cheruku). Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom https://doi.org/10.1016/j.jallcom.2019.02.269 0925-8388/© 2019 Elsevier B.V. All rights reserved. Journal of Alloys and Compounds 788 (2019) 779e786