Preparation of Perovskite Conductive LaNiO3 Films by Sol-Gel Techniques
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Preparation of Perovskite Conductive LaNiO3 Films by Sol-Gel Techniques Pei-Ying Lai, and Jen-Sue Chen Department of Materials Science and Engineering, National Cheng Kung University, No.1,Ta-Hsueh Road,Tainan,Taiwan,ROC., Tainan, Taiwan ABSTRACT Metallic thin films of LaNiO3 (LNO) have been prepared by the sol-gel method using lanthanum nitrate [La(NO3)3⋅6H2O] and nickel acetate [Ni(CH3COO)2⋅4H2O] as raw materials. X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and electrical measurements were used to characterize the multilayer LNO thin films. The perovskite phase appears after annealing at temperatures above 600 °C. LNO thin films are n-type metallic oxide. The lowest resistivity is 621 µΩ-cm after annealing at 600 °C, and the carrier concentration is 6.09×1022/cm3. INTRODUCTION Perovskite oxides are systems rich in physical characteristics such as ferroelectricity, superconductivity, catalysis, and giant magnetoresistance.1 Recently, it is noted that conductive perovskite oxides, for example, La1-xSrxCoO3(LSCO), and BaRuO3, have great potential as electrodes of ferroelectric materials for significant improvement on the fatigue problems.2-3 The reason for this is that conductive perovskite oxides are compatible to the insulating perovskite ferroelectrics, both chemically and crystallographically. Lately, particular some attention has been focused on the fabrication of conductive LaNiO3 (LNO) thin films. LNO is a pseudocubic perovskite with a lattice parameter of 3.84 Å and good metallic conductivity (bulk resistivity ~ 250 µΩ-cm at 300K).4-5 It is expected that the ferroelectric films on the compositionally and structurally compatible bottom electrodes would have excellent electrical properties. LNO films have been prepared by both physical and chemical techniques, such as pulsed laser deposition (PLD), metal-organic decomposition (MOD), sputtering, sol-gel, etc.6-9 Of these, sol-gel and MOD processes show attractive advantages over the others due to the fact that films with extremely uniform composition over large areas can be obtained with simple non-vacuum equipment. In the typical sol-gel method based on metal alkoxide, principal drawbacks include the relative hydrolysis rates10 and the flammability and the heat evolved in the exothermic decomposition reaction of metal alkoxides precursors. For economical reasons a process is desired in which metal salts are applicable as well, since these are generally cheaper. Therefore, in this work, we used nitrate and acetate as the starting materials to substitute for the conventional metal alkoxide precursors. The conductivity and binding configurations of the LNO thin films, which were spin-coated on Si, are characterized in the study.
EXPERIMENTAL DETAILS Lanthanum nitrate [La(NO3)3⋅6H2O] (0.03 mol) and nickel acetate [Ni(CH3COO)2⋅4H2O] (0.03 mol) were used as starting materials. They were mixed in a molar ratio of La : Ni=1 : 1 and dissolved in 2-methoxyethanol with heating and stirring. The concentration of the res
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