Significant increase in humidity sensing characteristics of praseodymium doped magnesium ferrite

doi:10.1016/j.sna.2011.03.010

Sensors and Actuators A: Physical

Volume 167, Issue 2, June 2011, Pages 332-337

https://doi.org/10.1016/j.sna.2011.03.010 Get rights and content

Abstract

Magnesium ferrite has been doped by Pr in 0.1 mol% and 0.3 mol% concentration for enhancing humidity sensing properties. The spin density/dangling bond calculated by electron paramagnetic resonance (EPR) increased from 8.15 × 10²⁰ to 15.6 × 10²⁰ for 0.3 mol% Pr doped compared to undoped magnesium ferrite sample. The bulk porosity of the samples in this case increases from 8.4% to 34% with Pr doping. Pr doping increased the sensitivity factor Z_10%/Z_90% from 24 to 113. Impedance gradient |dlog Z/dRH| at low 10–30% RH and high 70–90% RH has been determined with respect to spin density and porosity for the samples. A maximum drift in humidity hysteresis of 22% RH is predominantly reduced to 2% RH by a 0.1 mol% Pr doping in magnesium ferrite. Such remarkable improvements identified this material as a strong candidate for humidity sensors.

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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Significant increase in humidity sensing characteristics of praseodymium doped magnesium ferrite

Abstract

Introduction

Section snippets

Experimental

X-ray diffraction

Conclusions

Acknowledgement

Sens. Actuators

Mater. Chem. Phys.

Sens. Actuators

Mater. Chem. Phys.

Ceram. Int.

Sens. Actuators

Sens. Actuators

Sens. Actuators

Thermochim. Acta

Sens. Actuators

Sens. Actuators

Sens. Actuators B

Mater. Chem. Phys.

Sens. Actuators

Humidity sensors

J. Am. Ceram. Soc.

Phys. Status Solidi

Characterization of ESR active sites on lithium chloride modified-mesoporous silica

J. Phys. Chem.

Catalytic reactivity of the lattice oxide ions of praseodymium oxide

Chem. Lett.