Electrical and magnetic properties of V₂O₅ microstructure formed by self-assembled nanorods

Highlights

• Vanadium pentoxide flower like microstructures formed by self-assembled nanorods was synthesized by Hydrothermal method.

• The temperature versus resistivity plot shows the semiconducting nature of the microstructure.

• The magnetic characterization shows the paramagnetic behavior with small component of ferromagnetic behavior due to presence of small amount of V⁺⁴ oxidation state of vanadium.

Abstract

In this study, the hydrothermal method is used for the synthesis of Vanadium pentoxide (V₂O₅) microstructure. Analysis stands for the growth of microstructure in only the orthorhombic phase. The dot pattern in SAED image shows the crystalline nature of microstructure. Raman analysis shows the layered structure of V₂O₅. The morphological study of V₂O₅ shows the flower-like microstructure formed by nanorods having diameter ~3 μm. The transport measurement study confirmed the semiconductor nature of the microstructure in the temperature range 200K ≤ T ≤ 380K, and by Arrhenius analysis, we find the activation energy as 185 meV in the temperature range 285K–380K. In the lower temperature range 200K–285K the system shows the variable range hopping conduction of the charge carriers. An anomalous magnetization response is also evidenced in these V₂O₅ specimen in a narrow temperature range of ~45–60K where the magnetic ground state is antiferromagnetic. Interestingly, this state is bounded by paramagnetic states both at high and low temperatures.

Introduction

V₂O₅ is one of the most promising transition metal oxide semiconductor having high anisotropic electrical and optical properties in its orthorhombic phase [1]. Because of its exceptional physical and chemical properties it is widely used for variety of applications such as gas sensor [2], Li-ion batteries [3], photo catalyst [4], electrochromic devices [5]. In recent time variety of synthesis methods are used for synthesis of different types of nano and microstructures of vanadium pentoxide such as hydrothermal synthesis [6,7], sol-gel method [8], thermal evaporation [9]. Among all the synthesis method of V₂O₅ nano/micro structure, hydrothermal method is the facile method for preparation of metal oxide with the porous structure in the pure form and this method is easy to synthesized for industrial production. Currently V₂O₅ is used as most versatile material for Li-ion battery due to its layered structure, stable and large reversible capacities [10], high energy density [11], environment friendly [12] and low cost [13] material in the series of transition metal oxides. The vanadium oxide is well known for their structural transformation and electronic phase transition such as metal to insulator (MIT) and metal to semiconductor (MIS) [14]. The study of the temperature dependent resistivity/conductivity of the V₂O₅ microstructured material is important for understanding the charge transport and the microscopic mechanism of the charge carrier transfer.

There are reports on the analysis of electrical and magnetic properties of V₂O₅ nanostructures [1,14,15]. Parida et al. [15] have reported the room temperature ferromagnetism in V₂O₅ nanoflower structures. In this report the observed ferromagnetic behavior of V₂O₅ nanoflowers is attributed to the oxygen vacancies in the nanoflower structure. Dreifus et al. [1] investigated the magnetic properties of V₂O₅ polycrystal, and concluded the existence of predominant paramagnetic behavior in the temperature ranging from 5K–300K with superimposed peak at 80K which is associated with an antiferromagnetic phase. However, a detailed and systematic study is needed to thoroughly analyze the electrical conduction mechanism involved, and the magnetic behavior of the V₂O₅ microstructures.

In this work, a facile hydrothermal method was adopted to synthesize V₂O₅ microstructure, and the prepared microstructures were characterized by using XRD, Raman spectroscopy, SEM, TEM and SAED. Further, we have performed the electrical and magnetic measurements of the prepared V₂O₅ microstructures using physical properties measurement system (PPMS). Herein, we have observed the two type of electrical transport mechanism, thermally activated band conduction in high temperature regime (T ≥ 285K) and variable range hopping conduction at lower temperature regime (T ≤ 285K). The experimentally observed behavior of V₂O₅ microstructure is going to discussed in this report along with magnetic characteristic of V₂O₅ which shows its anomalous behavior in a narrow temperature range 45K–60K, where the magnetic ground state is antiferromagnetic.