preparation, characterization and dielectric properties of ba3m0.33ta4.67o15 (m=zn, ni) ceramics

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JOURNAL OF MATERIALS SCIENCE: MATERIALS IN ELECTRONICS 15 (2004) 695±697 Preparation, characterization and dielectric properties of Ba 3 M 0.33 Ta 4.67 O 15 (MZn, Ni) ceramics HUI ZHANG 1,2 , L. FANG 1,2 * , T. H. HUANG 1 , R. Z. YUAN 1 , RICHARD DRONSKOWSKI 2 1 State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, People's Republic of China 2 Institute of Inorganic Chemistry, RWTH Aachen University, 52056 Aachen, Germany E-mail: [email protected] Two novel Ba 3 M 0.33 Ta 4.67 O 15 (MZn, Ni) ceramics were prepared by conventional high temperature solid-state reactions and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and dielectric measurements methods. Both compounds are paraelectric phases of the ®lled tetragonal tungsten±bronze (TB) structure at room temperature. At 1 MHz Ba 3 Zn 0.33 Ta 4.67 O 15 and Ba 3 Ni 0.33 Ta 4.67 O 15 ceramics show high dielectric constants of 108 and 101 combined with low dielectric loss of 0.0052 and 0.0029, respectively. # 2004 Kluwer Academic Publishers 1. Introduction Recently, dielectric ceramics of high dielectric constant, high Q-values and good stability of temperature coef®cient of resonant frequency have been extensively studied because of their applications in discrete and multilayer (MLC) capacitors, microwave telecommuni- cation applications and satellite broadcasting [1±4]. The high dielectric constant materials are also very important in advanced microelectronics technologies such as dynamic random access memories (DRAM) [5]. So far, many dielectric materials have been studied such as Ba(Zn 1=3 Ta 2=3 )O 3 , Ba 2 Ti 9 O 20 , (Zr, Sn)TiO 4 , rare earth titanates in BaO±Re 2 O 3 ±TiO 2 . However, those materials e5 100 are insuf®cient for miniaturization of microelectric devices. Hence, the development of new materials with dielectric constants in excess of 100 has become very important. Recently, Koshy and Chen et al., respectively, reported some TB ceramics such as Ba 3 R 3 Ti 5 Nb 5 O 30 , Ba 5 RTi 3 Ta 7 O 30 , Sr 5 RTi 3 Ta 7 O 30 and Ba 3 R 3 Ti 5 Ta 5 O 30 (R 55 La, Nd, Sm) which have high dielectric constant above 100 and low loss [6±12]. Considering the perovskite ceramic Ba(Zn 1=3 Ta 2=3 )O 3 in BaO±ZnO±Ta 2 O 5 system which is extremely important for applications at high frequency ( 4 10 GHz) and at high power due to its high Q-values and near zero temperature coef®cient [3], the materials with TB structure in this system might possess useful dielectric properties. Extensive literature survey on TB compounds reveals that, even though a lot of work has been done on the compounds of this family, not much has been reported on the compounds with TB structure in the BaO±MO±Ta 2 O 5 (M55Zn, Ni) system, and as there is no report on the titled compounds. This paper ®rst presents the preparation, characterization and dielectric properties of two TB compounds Ba 3 Zn 0:33 Ta 4:67 O 15 and Ba 3 Ni 0:33 Ta 4:67 O 15 . 2. Experimental High purity powders of BaCO 3 ( 4 99.5%), ZnO ( 4 99.95%), NiO ( 4 99.5%), and Ta 2 O 5 ( 4 99.9%) were weighed to Ba 3 M 0:33 Ta 4:67 O 15 (MZn, Ni) stoichiometry, respectively. The compounds with M as Zn and Ni will be referred to as BZT and BNT, respectively in the remaining part of the paper. The powders were mixed and ground for 24 h in ethanol using a ball mill with zirconia media, then dried and calcined at 1400 C for 8 h. The calcined powders were reground and mixed with an organic binder of 5 wt % polyvinyl alcohol (PVA), and then pressed into disks of 11mm diameter and about 2±4 mm thickness at a pressure of 200 MPa. The discs were sintered in air at 1450 C for 4 h to yield dense ceramics. The bulk densities of the compacts were measured by the Archimedes method. Crystalline phases of the sintered samples were identi®ed by a Rigaku D/MAX- RB X-ray diffractiometer (XRD) using CuKa radiation l 0.154 06 nm, and the microstructure was observed using a JSM-5610LV scanning electron microscope (SEM). Silver paste was applied to the circular faces, then dried at 600 C for 20 min and cooled naturally to room temperature. The temperature-dependent dielectric measurements were made using an HP4284A LCR meter equipped with a thermostat from room temperature *Author to whom all correspondence should be addressed. 0957±4522 # 2004 Kluwer Academic Publishers 695

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