Influence of Ba and Mo co-doping on the structural, electrical, magnetic and optical properties of BiFeO<sub>3</sub> ceramics
Aungkan Sen, M.K. Hasan, Zahidul Islam, Md Rahat Al Hassan, Tasmia Zaman, Md. Abdul Matin, Fahmida Gulshan
Abstract
Abstract: In this work, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">Bi</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0.8</mml:mn> </mml:mrow> </mml:msub> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">Ba</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0.2</mml:mn> </mml:mrow> </mml:msub> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">Fe</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>1</mml:mn> <mml:mo>−</mml:mo> <mml:mi>x</mml:mi> </mml:mrow> </mml:msub> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">Mo</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>x</mml:mi> </mml:mrow> </mml:msub> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">O</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msub> </mml:math> (x = 0, 0.5, 0.10 and 0.15) ceramics were synthesized by conventional solid-state reaction to evaluate the influence of Ba 2+ and Mo 6+ co-doping on the structure, morphology, electrical, magnetic and optical properties of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">BiFeO</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msub> </mml:math> ceramic. Rietveld refinement of x-ray diffraction data was done to obtain the subtle structural information. A tetragonal structure of P4mm type was revealed for <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">Bi</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0.8</mml:mn> </mml:mrow> </mml:msub> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">Ba</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0.2</mml:mn> </mml:mrow> </mml:msub> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">FeO</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msub> </mml:math> (x = 0) ceramic. Evolution of rhombohedral (R3c) phase was observed with Mo 6+ doping and a complete transformation to R3c phase from P4mm was found for 15 wt% Mo 6+ doping. This type of transformation causes distortion in the structure and results in changing bond angle. Magnetization was found to be improved with increasing the percentage of Mo 6+ up to 10 wt%. Canting of spin due to the change in Fe-O-Fe bond angle is believed to be the main reason behind this improvement. One secondary phase <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">BaMoO</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>4</mml:mn> </mml:mrow> </mml:msub> </mml:math> was found and becomes prominent with Mo 6+ doping. Possible formation of this impurity and its correlation with properties are explained. Microstructural analysis was done to observe the Ba 2+ and Mo 6+ co-doping effect on grain size and distribution. A correlation of grain size with electric and magnetic properties is drawn and elucidated. Dielectric constant shows an increasing trend with Mo 6+ doping. Reduction in oxygen vacancy, due to charge compensation upon high charged Mo 6+ addition, believed to be the staple reason behind the dielectric constant increment. Lastly, optical band gap energy found to be decreased with the addition of Mo 6+ and possible reasons behind this are evaluated. Overall, co-doping of Ba 2+ and Mo 6+ found to have a positive influence over materials electrical, optical as well as magnetic property.