Band Structure and Thermoelectric Properties of Ni
(x)Zn
(1-x)Fe
2O
4LIM Joon Hoong
1,a*1School of Engineering, Taylor’s University, 47500, Subang Jaya, Selangor, Malaysia
Keywords: Seebeck coefficient; thermal conductivity; electrical conductivity; Ni(x)Zn(1-x)Fe2O4; band structures.
Abstract. Thermoelectric materials has made a great potential in sustainable energy industries, which enable the energy conversion from heat to electricity. The band structure and thermoelectric properties of Ni(x)Zn(1-x)Fe2O4 have been investigated. The bulk pellets were prepared from analytical grade ZnO, NiO and Fe2O3 powder using solid-state method. It was possible to obtain high thermoelectric properties of Ni(x)Zn(1-x)Fe2O4 by controlling the ratios of dopants and the sintering temperature. XRD analysis showed that the fabricated samples have a single phase formation of cubic spinel structure. The thermoelectric properties of Ni(x)Zn(1-x)Fe2O4 pellets improved with increasing Ni. The electrical conductivity of Ni(x)Zn(1-x)Fe2O4 pellets decreased with increasing Ni content. The electrical conductivity of Ni(x)Zn(1-x)Fe2O4 (x = 0.0) is (0.515 x 10-3 Scm-1). The band structure shows that ZnxCu1-xFe2O4 is an indirect band gap material with the valence band maximum (VBM) at M and conduction band minimum (CBM) at A. The band gap of Ni(x)Zn(1-x)Fe2O4 increased with increasing Ni content. The increasing band gap correlated with the lower electrical conductivity. The thermal conductivity of Ni(x)Zn(1-x)Fe2O4
pellets decreased with increasing Ni content. The presence of Ni served to decrease thermal conductivity by 8 Wm-1K-1 over pure samples. The magnitude of the Seebeck coefficient for Ni(x)Zn(1-x)Fe2O4 pellets increased with increasing amounts of Ni. The figure of merit for Ni(x)Zn(1- x)Fe2O4 pellets and thin films was improved by increasing Ni due to its high Seebeck coefficient and low thermal conductivity.
Introduction
The increasing awareness of greenhouse effect and global warming caused by conventional power generation has led to a growing demand to search for alternative energy resources [1].
Thermoelectric materials has made a great potential in sustainable energy industries, which enable the energy conversion from heat to electricity [2]. These thermoelectric materials work as a solid state devices that have no moving parts, environmentally friendly and reliable. Then the main drawback of the existing thermoelectric materials is their relatively low efficiency in energy conversion. The efficiency of thermoelectric materials depend on the dimensionless figure of merit that depend on the Seebeck coefficient, electrical conductivity and thermal conductivity which can divided to the electronic part and lattice part [3]. Seebeck coefficient, electrical conductivity and thermal conductivity are related to the electronic structure of the material and thermal lattice part is related to its phonon vibration [4,5].
One way to optimize energy conversion efficiency is to reduce the lattice thermal conductivity without altering the electronic transport properties of the material [6]. This method can be explored by controlling doping, alloying and nano-composition for phonon scattering enhancement [7].
Another method is to enhance the power factor of the materials which consists of the Seebeck coefficient and electrical conductivity properties. The Seebeck coefficient of a material is determined by density of state (DOS) effective mass and carrier density [8]. The electrical conductivity is determined by carrier density and carrier mobility which is related to electron scattering in crystal lattice. The enhancement might be achieved by optimizing the band structure and electron scattering of the materials by controlling doping [9,10]. The Seebeck coefficient and electrical conductivity are interrelate, where an increase in carrier density tends to increase the electrical conductivity and decrease the Seebeck coefficient. The effective mass had similar effect,
Solid State Phenomena Submitted: 2020-05-29
ISSN: 1662-9779, Vol. 317, pp 28-34 Revised: 2020-06-18
© 2021 Trans Tech Publications Ltd, Switzerland Accepted: 2020-07-16
Online: 2021-05-10
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications Ltd, www.scientific.net. (#550658056-15/01/21,05:16:19)
