Significant increase in humidity sensing characteristics of praseodymium doped magnesium ferrite
Introduction
Ceramic oxides have been used as humidity sensitive materials due to their porous microstructure [1], [2], [3], [4]. In addition to porous microstructure, defects and vacancies, dangling bonds on oxide surfaces are the most active sites for low concentration water vapor dissociation. The dissociation of water vapors releases protons for conduction hence resistance of the sensing material decreases. In order to enhance surface activity, surface additives or dopants are incorporated in oxides to enhance the humidity sensing performance [5], [6], [7], [8]. The improvement in humidity sensitivity of ferrates and aluminates with increased spin density/dangling bonds has been studied [9]. The increase in hydrogen adsorption measured by electron spin resonance (ESR) on active sites is also reported [10]. Some catalytic ions have been also adopted to enhance the surface charge density [11], [12].
Magnesium ferrite is a porous and highly resistive, chemically and thermally stable ferrite [13], [14]. Researchers explored the physical and electrical properties of MgFe2O4 for humidity sensing [15], [16], [17]. In this work Pr doping in nominal amounts 0.1 mol% and 0.3 mol% in magnesium ferrite to increase its porosity and spin density/dangling bonds for enhancing humidity sensing properties have been studied. A drop in impedance increased to 2–3 orders of magnitude (108/109 to 106 Ω) besides sustaining linearity by Pr doping to magnesium ferrite has been recorded. Humidity hysteresis drastically decreased by such a nominal Pr doping in magnesium ferrite.
Section snippets
Experimental
Analytical grade MgCO3 and Fe2O3 were mixed in a ratio 1:1, and were ground in a mechanical ball mill using zirconium balls. A 0.1% and 0.3 mol% Pr6O11 was mixed in precursor respectively to obtain different samples, followed by grinding for 2 h. The three compositions samples were presintered at a temperature of 850 °C in air for 8 h. The presintered powder was further ground and pellets were pressed in a rectangular 15 mm × 3 mm × 2 mm size followed by sintering at 1000 °C in air for 4 h. The details of
X-ray diffraction
The X-ray diffraction of the sintered pellets was measured at room temperature within 20–70°, 2θ range using a Bruker AXS configuration operating at 40 kV, 40 mA with Cu Kα radiation in a step angle 0.002°. All the peaks recorded in the XRD plot coincide with a spinel magnesium ferrite structure, JCPDS Card No. 36-0398, as shown in Fig. 1. Due to Pr doping, XRD shows shifting of peak towards higher angle side and decrease in intensity of peaks as shown in Fig. 1 (inset). Peak shift attributes to
Conclusions
In this study, a nominal doping of Pr in magnesium ferrite remarkable improved its humidity sensing properties. With praseodymium doping, both spin density and porosity of magnesium ferrite has increased. It resulted into increase in lower concentration 10–30% RH water vapor dissociation, hence the lower water vapor sensitivity improved. Increased porosity due to doping has improved its sensitivity towards high humidity 70–90% RH range. Thus, Pr doping in magnesium ferrite has enhanced wide
Acknowledgement
The authors are thankful to Director “National Physical Laboratory” New Delhi for providing constant encouragement, motivation, and support to carry out this work. Ms. Jyoti Shah is thankful to CSIR for granting fellowship to pursue research work.
Ms. Jyoti Shah received Ph.D. in humidity sensing properties of magnesium ferrite from Gurukula Kangri Vishwavidyalaya (Deemed Uni.) Haridwar. Presently she is research associate at National Physical Laboratory, New Delhi. Her research interest is in humidity sensing materials, magnetic materials and DMS materials.
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Ms. Jyoti Shah received Ph.D. in humidity sensing properties of magnesium ferrite from Gurukula Kangri Vishwavidyalaya (Deemed Uni.) Haridwar. Presently she is research associate at National Physical Laboratory, New Delhi. Her research interest is in humidity sensing materials, magnetic materials and DMS materials.
Dr. Manju Arora received her Ph.D. on Vibrational spectroscopy of Some Rare Earth Compounds from CCS University, Merrut. Presently she is working as a senior technical officer in EPR group at National Physical Laboratory, New Delhi. Her current research work is on synthesis of nanocrystalline ZnO thin films, nanomagnetic particles and their characterization by EPR, FTIR and FT Raman spectroscopy.
Dr. L.P. Purohit did his Ph.D. on semi conducting materials from Delhi University. Currently he is working as a reader in Gurukula Kangri Vishwavidyalaya (Deemed Uni.) Haridwar. His current research interest is on bulk and thin films of semiconducting materials and oxide magnetic materials.
Dr. R.K. Kotnala obtained Ph.D. degree in solar cell from Indian Institute of Technology, Delhi in 1982. At present he is working as a senior scientist in National Physical Laboratory, New Delhi, India. His current field of interest is magnetic materials, standards, sensor materials, and spintronic materials.