Preparation of Ba(Mg 1/3 Nb 2/3 )O 3 ceramics as microwave dielectrics through alkoxide-hydroxide route
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Ba(Mg1/3Nb2/3)O3 powders were prepared through an alkoxide-hydroxide route. Their sintering behavior and crystallographic structures were investigated, and microwave properties of the obtained ceramics were also measured. Crystalline powder with approximately 0.5 ^m in particle size was obtained by the reaction of Ba(OH) 2 -8H 2 O and Mg-Nb double alkoxide, Mg[Nb(OEt)6]2, in ethanol-acetone solution. A powder compact sintered at 1350 °C for 2 h showed >99% of relative density and >0.9 of ordering degree of the B site. The Q value of Ba(Mg1/3Nb2/3)O3 ceramics was sensitive to sintering conditions due to the formation of an impurity phase. The ceramics sintered at 1350 °C for 5 h showed a dielectric constant e of 32 and Q value of > 13 000 at 11.8 GHz. The temperature coefficient of resonant frequency 17 was 23.9 ppm/°C at 9.8 GHz. I. INTRODUCTION Complex perovskite compounds on the basis of Ba(B1/3B'2/3)O3 (B = Mg,Zn; B ' = Ta,Nb) structure have been reported to possess excellent microwave properties.1"7 In particular, Ba(Mg1/3Ta2/3)O3 (BMT) 1 shows a dielectric constant e of 25, Q value of 16 800 at 10.5 GHz, and 4.4 ppm/°C as the temperature coefficient of resonant frequency, 17, and Ba(Mgi/ 3 Nb 2/3 )O 3 (BMN) 3 shows e of 32, Q value of 5600 at 10.5 GHz, and Tf of 33 ppm/°C. However, to obtain dense ceramics with excellent microwave properties, sintering additives such as Mn 1 or a rapid sintering method8'9 are necessary because these compounds are poorly sinterable. Most of them have an ordered hexagonal structure, and ordering on the B site affects the Q value of complex perovskite. Recently, the metal alkoxide method has been applied to prepare perovskite ceramics10"12 such as BaTiO3 or SrTiO3 and other electric ceramics13"15 since easily sinterable powders with fine particles were obtained. Kiss et al. obtained BaTiO3 powder by the hydrolysis of Ti alkoxides using Ba(OH) 2 aqueous solution.10 Mazdiyasni et al. prepared BaTiO3, SrTiO3, and SrZrO3 powders with particle size of about 10 nm by the hydrolysis of mixed-alkoxide solutions.11'12 In complex perovskite systems, a number of studies on Pb(Mg1/3Nb2/3)O3 ceramics as a relaxer have been carried out,16"18 but not on the complex perovskite containing Ba atom on the A site as microwave dielectrics. ^Present address: Technical Research Center, Krosaki Corporation, 1-1 Higashihama, Yahata-nishi, Kitakyushu 806, Japan. ''Present address: Advanced Materials & Research Laboratory, Nippon Steel Corporation, 1618 Ida, Nakahara, Kawasaki 211, Japan. c 'Present address: Research and Development Center, NGK Spark Plug Corporation Ltd., 2808 Iwasaki, Komaki 485, Japan. J. Mater. Res., Vol. 7, No. 7, Jul 1992 http://journals.cambridge.org
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In the present paper, a preparation method of BMN ceramics, a complex perovskite compound expected to have excellent microwave properties, was examined. An alkoxide-hydroxide method was established to obtain easily sinterable powders. We found that crystalline powder was prepared from Ba(OH) 2 -8H 2 O and Mg-Nb
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