Comparative study of structural and optical properties of zirconium-doped indium oxide synthesized by solid state reactions and sol-gel technique

O. Nemeș, J. Chelaru, K. Magyari, L. Bizo
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引用次数: 1

Abstract

In the present work the effect of zirconium doping (1.5 at.%) on the structural and optical properties of indium zirconium oxide was studied. Zr-doped indium oxides were prepared by using two different methods, solid state reactions and sol-gel technique. The compositions with bixbyite structure have been synthesized by two different methods, solid state reactions in air and sol-gel process. X-ray powder diffraction (XRPD) used for phases analysis confirm the validity of the cubic bixbyite-type structure of In2O3. The optical properties of the prepared composition were considered in terms of their diffuse reflectance spectra (DRS). The morphology of crystals was evidenced by SEM analyses and reveal agglomeration of particles with their size ranges in the micrometer domain. Introduction Transparent conducting oxides (TCOs) are an important class of materials which have attracted much attention in the last years due to their main properties, low resistivity and high optical transparency. The dominant TCOs are mainly zinc oxide (ZnO), indium oxide (In2O3) and tin oxide (SnO2), as well as subsequent mixtures of these, such as well-known indium tin oxide (ITO) [1]. In2O3, a wide-bandgap n-type semiconductor, is widely used in various applications due to their properties including solar applications, the transparent electrodes in various optoelectronic devices, the flat panel liquid crystals displays, the barrier layers in tunnel junctions, the active layers of gas sensors or the material for ultraviolet lasers [2]. Therefore, the physical properties of the In2O3, like high electrical conductivity and optical transparency in the visible range, strongly depend on the preparation method. For this reason there are many investigations which are studying their properties in dependence on the synthesis methods. These methods include physical methods such as sputtering, evaporation, pulsed laser deposition, spray pyrolysis, as well as chemical methods like chemical pyrolysis, chemical vapor deposition, sol-gel, bath deposition and electroplating [3–8]. On the other hand electrical properties of In2O3 can be improved by doping with metallic donor impurity. For this reason the system ZrO2–In2O3 was mostly investigated [810]. Powder Metallurgy and Advanced Materials – RoPM&AM 2017 Materials Research Forum LLC Materials Research Proceedings 8 (2018) 167-172 doi: http://dx.doi.org/10.21741/9781945291999-19 168 In the present paper we comparatively investigated the structural evolution, optical and morphological properties of indium zirconium oxide prepared by two methods, solid state synthesis and sol-gel route. Materials and Methods Synthesis Two different preparation methods were employed in the synthesis of zirconium-doped indium oxide: solid state synthesis and sol-gel method. Compositions belonging to In2-xZrxO3 (0.025 ≤ x ≤ 0.15) system with the bixbyite structure were prepared by solid state reactions from mixtures of pure In2O3 (Alfa Aesar 99.995%) and ZrO2 (Alfa Aesar 99%) at 1400 °C, in air. In the sol-gel synthesis indium (III) nitrate hydrate (In(NO3)2·xH2O) was used as a precursor and zirconium (IV) chloride (ZrCl4) as a doping source at the molar ratios required to obtain In2O3 doped with 1.5 at % ZrO2. Aqueous solutions of the two salts were stirred on a warming plate at 80 °C in order to mix the solution uniformly. The sol was prepared using isopropyl alcohol as solvent and ethylene glycol or sucrose as polymerization agent. The sucrose solution was added gradually into the aqueous solutions under stirring until colloidal suspensions were obtained. The sol continuously transformed into wet gel and then dried gel under heating at 100 °C during 24h. The resulted dried materials were annealed at 600 °C in air for one hour to form the required Zrdoped indium oxide. Fig. 1 presents schematic flow chart of indium zirconium oxide obtained by solid state synthesis.
固相反应与溶胶-凝胶法制备掺锆氧化铟的结构与光学性能比较研究
本文研究了锆(1.5% at.%)掺杂对氧化锆铟结构和光学性能的影响。采用固相反应和溶胶-凝胶法制备了掺杂zr的氧化铟。采用空气固相反应和溶胶-凝胶法制备了具有bixbyite结构的化合物。x射线粉末衍射(XRPD)相分析证实了In2O3的立方bixbyite型结构的有效性。根据其漫反射光谱(DRS)来考虑所制备组合物的光学性质。通过扫描电镜分析证实了晶体的形态,并发现颗粒的团聚,其尺寸范围在微米范围内。透明导电氧化物(TCOs)是近年来备受关注的一类重要材料,其主要特性是低电阻率和高光学透明度。主要的tco主要是氧化锌(ZnO)、氧化铟(In2O3)和氧化锡(SnO2),以及它们的后续混合物,如众所周知的氧化铟锡(ITO)[1]。In2O3是一种宽带隙的n型半导体,由于其特性,包括太阳能应用、各种光电器件中的透明电极、平板液晶显示器、隧道结中的阻挡层、气体传感器的有源层或紫外激光器的材料等,被广泛应用于各种领域[2]。因此,In2O3的物理性能,如高导电性和可见光范围内的光学透明度,很大程度上取决于制备方法。因此,许多研究都是根据合成方法来研究它们的性质。这些方法包括溅射、蒸发、脉冲激光沉积、喷雾热解等物理方法,以及化学热解、化学气相沉积、溶胶-凝胶、镀液沉积、电镀等化学方法[3-8]。另一方面,掺杂金属给体杂质可以改善In2O3的电学性能。因此对ZrO2-In2O3体系的研究较多[810]。粉末冶金与先进材料- RoPM&AM 2017 Materials Research Forum LLC Materials Research Proceedings (2018) 167-172 doi: http://dx.doi.org/10.21741/9781945291999-19 168本文比较研究了固态合成和溶胶-凝胶两种方法制备的氧化锆铟的结构演变、光学和形态学性质。采用固体合成法和溶胶-凝胶法两种不同的制备方法合成了掺杂锆的氧化铟。将纯In2O3 (Alfa Aesar 99.995%)和ZrO2 (Alfa Aesar 99%)在空气中于1400℃固相反应制备出具有bixbyite结构的In2-xZrxO3(0.025≤x≤0.15)体系。在溶胶-凝胶合成中,以硝酸水合铟(III) (In(NO3)2·xH2O)为前驱体,氯化锆(ZrCl4)为掺杂源,摩尔比为1.5% (% ZrO2)掺杂得到In2O3。两种盐的水溶液在80℃的加热板上搅拌,使溶液混合均匀。以异丙醇为溶剂,乙二醇或蔗糖为聚合剂制备溶胶。将蔗糖溶液在搅拌下逐渐加入到水溶液中,直至得到胶状悬浮液。在100℃下加热24h,连续转化为湿凝胶,再转化为干凝胶。将得到的干燥材料在空气中600℃退火1小时,形成所需的掺杂氧化铟。图1为固态合成氧化锆铟的原理流程图。
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