Dielectric Characteristics of Donor Doped Nonlead Ba(Cu 1/3 Nb 2/3 )O 3 Perovskite Material Synthesized by Microwave-ass
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0997-I06-05
Dielectric Characteristics of Donor Doped Nonlead Ba(Cu1/3Nb2/3)O3 Perovskite Material Synthesized by Microwave-assisted Citrate-nitrate Sol-gel Route Alp Manavbasi and Jeffrey C LaCombe Chem. & Met. Engineering, University of Nevada, Reno, Reno, NV, 89557
ABSTRACT Nonlead perovskite type, Ba(Cu1/3Nb2/3-xWx)O3 (x = 0, 0.025), ferroelectric ceramic powders (BCN) were prepared by the microwave-assisted citrate-nitrate sol-gel technique. The gel was formed from a stable and homogeneous sol prepared by mixing stable solutions of barium- and copper-nitrate, tungsten citrate, and peroxo-citrato-niobium precursors. Microwave irradiation of the gel resulted in a dark, fluffy precursor material after auto-combustion. Calcination of the as-combusted samples produces a single phase with tetragonal splitting in XRay diffraction patterns. The crystallite size of the synthesized samples was found to be 41 nm. Particle morphology and the size of nanocrystalline powders were characterized by scanning electron microscopy and photon correlation spectroscopy, respectively. Electrical and dielectric properties of sintered samples were investigated by impedance spectroscopy. The isothermal ac measurements were performed from room temperature, up to 600 ∫C for W6+ doped and undoped BCN samples. INTRODUCTION No compound has been found to be superior to Pb(Zr,Ti)O3 regarding the piezo and ferroelectric properties. However, concerns over the use of hazardous heavy metals such as Pb and Cd may lead to restrictions on their use in electrical and electronic equipment in the European and other markets (see for example, RoHS directive [1]). Therefore, there is an interest in development of lead-free electronic materials. Ba(Cu1/3Nb2/3)O3 (BCN) is a ferroelectric compound with tetragonal perovskite-type structure and has a high curie temperatureóabove 500 ∞C [2,3]. However, it has been reported that BCN has very low resistivity at room temperature (1.6 × 104 Ω∑m), making the measurement of ferroelectric properties [3] problematicóand resistivity only decreases further with increasing temperature. This sharp increase in conductivity was attributed to the eutectic transformation of CuO to Cu2O in samples sintered above 1075 ∞C [2]. Introduction of a few wt% ZnO, B2O3, and sintering at temperatures less than 1000 ∞C resulted in an increase in the resistivity of the compound [3]. Suppression of oxygen vacancies from the perovskite structure such as W6+ substitution can possibly enhance the dielectric and electrical properties [4]. Reports on the preparation of single phase BCN with sufficiently resolved tetragonal splitting are mostly based on the application of conventional solid state methods with extended hours of milling and high temperature heat treatment [2,5]. Alternatively, thermal decomposition of freeze-dried oxalate precursor was reported for synthesis of the BCN phase at low temperatures [6]. Aqueous sol-gel preparation of mixed oxides containing pentavalent metals like Nb is very complicated because of the high valency and
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