A Novel Approach to the Sintering Schedule of Ba (Co0.7Zn0.3)1/3Nb2/3O3 Dielectric Ceramics for Microwave Applications (original) (raw)
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Applied Sciences, 2015
The effects of post-annealing on the crystal structure, microstructure, and microwave dielectric properties for Ba(Co 0.7 Zn 0.3) 1/3 Nb 2/3 O 3 ceramics were investigated. The as-prepared materials were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The microwave dielectric properties are measured at 6 GHz using a network analyzer. Ba 5 Nb 4 O 15 and/or Ba 8 (Co,Zn) 1 Nb 6 O 24 secondary phases were found on the surface according to sintering conditions due to volatilization of some Zn and Co elements. The experimental results show that the beneficial effect of the annealing steps to improved the microwave dielectric properties. Excellent microwave dielectric properties were achieved for the coarse-grained microstructures by a higher sintering temperature and with a shorter holding time followed by annealing steps at lower temperatures with a longer holding time. This improvement can be attributed to 1:2 cation ordering within the crystal, which is taking place during annealing process. The Ba(Co 0.7 Zn 0.3) 1/3 Nb 2/3 O 3 ceramic could be used successfully for realization of dielectric microwave resonators, since it has a high quality factor Q f value of 123,700 GHz, a high dielectric constant ε r value of 34.5 and a temperature coefficient of the resonant frequency τ f of 0 ppm/ ¥ C.
Journal of the American Ceramic Society, 2006
BaCu(B 2 O 5) ceramics were synthesized and their microwave dielectric properties were investigated. BaCu(B 2 O 5) phase was formed at 7001C and melted above 8501C. The BaCu(B 2 O 5) ceramic sintered at 8101C had a dielectric constant (e r) of 7.4, a quality factor (Q Â f) of 50 000 GHz and a temperature coefficient of resonance frequency (s f) of À32 ppm/1C. As the BaCu(B 2 O 5) ceramic had a low melting temperature and good microwave dielectric properties, it can be used as a low-temperature sintering aid for microwave dielectric materials for low temperature co-fired ceramic application. When BaCu(B 2 O 5) was added to the Ba(Zn 1/3 Nb 2/3)O 3 (BZN) ceramic, BZN ceramics were well sintered even at 8501C. BaCu(B 2 O 5) existed as a liquid phase during the sintering and assisted the densification of the BZN ceramic. Good microwave dielectric properties of Q Â f 5 16 000 GHz, e r 5 35, and s f 5 22.1 ppm/1C were obtained for the BZN16.0 mol% BaCu(B 2 O 5) ceramic sintered at 8751C for 2 h.
Ceramics International, 2008
The sintering behavior and dielectric properties of the monoclinic zirconolite-like structure compound Bi 2 (Zn 1/3 Nb 2/3) 2 O 7 (BZN) and Bi 2 (Zn 1/ 3 Nb 2/3Àx V x) 2 O 7 (BZNV, x = 0.001) sintered under air and N 2 atmosphere were investigated. The pure phase were obtained between 810 and 990 8C both for BZN and BZNV ceramics. The substitution of V 2 O 5 and N 2 atmosphere accelerated the densification of ceramics slightly. The influences on microwave dielectric properties from different atmosphere were discussed in this work. The best microwave properties of BZN ceramics were obtained at 900 8C under N 2 atmosphere with e r = 76.1, Q = 850 and Q f = 3260 GHz while the best properties of BZNV ceramics were got at 930 8C under air atmosphere with e r = 76.7, Q = 890 and Q f = 3580 GHz. The temperature coefficient of resonant frequency t f was not obviously influenced by the different atmospheres. For BZN ceramics the t f was À79.8 ppm/8C while t f is À87.5 ppm/8C for BZNV ceramics.
Ba(Zn1/3Ta2/3)O3 Ceramics for Microwave and Millimeter-wave Applications
Annals of the New York Academy of Sciences, 2009
The Ba(Zn 1/3 Ta 2/3 )O 3 (BZT) ceramic samples were prepared by solid-state reaction and sintered in the range 1550-1650 • C for 2 h. Several methods-X-ray diffraction (XRD) and scanning electron microscopy (SEM)-were used for structural and morphological characterization. The unit cell distortion and the presence of the secondary phase content were studied by XRD. A long-range order with a 2:1 ratio of Ta and Zn cations on the octahedral positions of the perovskite structure was noticed with the increase of the sintering temperature. SEM investigations revealed polyhedral well-faceted grains and large grain size distribution. The dielectric properties in the microwave range were measured at room temperature and at 1 kHz on a large temperature interval (±150 • C). The dielectric parameters were correlated with morphological and structural properties. Ceramic samples were annealed at 1410 • C for 30 h to improve the microwave properties. The dielectric constant of BZT samples measured at 6 GHz and at 1 kHz was between 27 and 28 on the whole temperature range, that is, typical values for BZT material. The temperature coefficient of the resonance frequency at 6 GHz exhibits positive values less than 6 ppm/ • C.
Ceramics International, 2013
The ZnO and V 2 O 5 co-doped Ba 3 Ti 2 (Mg 1/3 Nb 2/3) 2 Nb 4 O 21 (BTMNN-2) microwave dielectric ceramics were successfully prepared via a conventional solid-state reaction method. The effect of the 2 ZnO-V 2 O 5 complex additive on the sintering temperature and microwave dielectric properties was specially investigated. The X-ray diffraction analysis reveals that the BTMNN-2 ceramics doped with 2 ZnO-V 2 O 5 form a single hexagonal structure phase without visible secondary phases. A small amount of 2 ZnO-V 2 O 5 additive can significantly lower the sintering temperature of BTMNN-2 ceramics owing to the formation of a liquid phase in the BTMNN-2 matrix, as clearly evidenced by the SEM micrographs. Meanwhile, the experimental results show that the microwave dielectric properties of the samples were strongly dependent on the densification, crystalline phases, and grain size. The 5 wt% 2 ZnO-V 2 O 5 doped BTMNN-2 ceramics can be sintered at 900 1C and own good microwave dielectric properties of e r ¼47, Q Â f ¼10,500 GHz and t f ¼ 16 ppm/1C, showing a potential for applications in mid-permittivity low temperature co-fired ceramics.
Effect of dopants on microwave dielectric properties of Ba(Zn1/3Nb2/3)O3 ceramics
Journal of the European Ceramic Society, 2007
Ba(Zn 1=3 Ta 2=3 )O 3 (BZT) has been prepared with various amounts of different dopants such as oxides of divalent, trivalent, tetravalent, pentavalent and hexavalent elements. Effect of these dopants on microwave dielectric properties of BZT is investigated. Some of the dopants are found to increase quality factor (Q). Most of the dopants increase the temperature coefficient of resonant frequency ( f ). Annealing undoped BZT increased the order parameter and quality factor. Small amounts of dopants such as that of oxides of Zr, Ga, Cr, Ce, Sn, In, Mn and Sb increased the quality factor. The doped ions substitute for the ordered B ions decreasing the order parameter. Annealing Ga and In doped BZT decreased the Q factor where as it increased for Zr, Cr, Ce, Sn, Mn, Sb doped samples. Doping BZT with Zr, Ga, Cr, Ce, Sn, In, Mn, Sb decreased the order parameter but at the same time increased the quality factor indicating that order parameter alone is a poor indicator of quality factor. The quality factor is found to depend on the dopant ionic radii and dopant concentration. The quality factor increased when the ionic radius of the dopant is close to the ionic radius of the B site ions Zn or Ta.
Ceramics International, 2013
In this work, the effects of various two-stage sintering schemes on phase formation, microstructural development and dielectric properties of Zn 3 Nb 2 O 8 ceramics were systematically determined via a combination of scanning electron microscopy (SEM), energydispersive X-ray (EDX) and dielectric measurement techniques. In comparison with the conventional sintered samples, it was found that single-phase Zn 3 Nb 2 O 8 ceramics with maximum density of 9999% theoretical density, smaller average grain size (99 3 mm) and better dielectric properties can be achieved via a two-stage sintering technique.
Ceramics International, 2011
Doped hexagonal BaTiO 3 (h-BaTiO 3) ceramics have recently been identified as potential candidates for use in microwave dielectric resonators. However, similar to other common microwave ceramics, doped h-BaTiO 3 ceramics require a sintering temperature higher than 1400 8C. In this study, the effects of Bi 2 O 3 and Li 2 CO 3 on the densification, microstructural evolution and microwave properties of hexagonal 12R-Ba(Ti 0.5 Mn 0.5)O 3 ceramics were examined. Results indicate that Bi 2 O 3 and Li 2 CO 3 are able to effectively reduce the sintering temperature of 12R-Ba(Ti 05 Mn 0.5)O 3 ceramics through liquid phase sintering while retaining the hexagonal structure and the microwave dielectric properties. The best results were obtained for the 12R-Ba(Ti 0.5 Mn 0.5)O 3 with the additions of 5 wt% Bi 2 O 3 sintered at 1200 8C
Journal of Materials Science: Materials in Electronics, 2013
Microwave sintering has emerged in recent years as a new method for sintering a variety of materials that has shown significant advantages against conventional sintering procedures. Sr and Pb doped BaTiO 3 ceramics has been prepared by the high energy ball milling followed by conventional and microwave sintering. The phase formation was confirmed by X-ray diffractometer followed by Scanning electron microscopy, atomic force microscopy and Transmission electron microscopy. Dielectric constant was measured on both the samples and it is observed that, in Ba 0.8 Pb 0.2 TiO 3 (abbreviated as BPT), it increased more than one order of magnitude and in Ba 0.8 Sr 0.2 TiO 3 (abbreviated as BST), it increased two orders of magnitudes at room temperature and Curie transition temperature by microwave sintering. Interestingly the Curie transition temperature of BPT value decreased from 224 to 210°C, where as in BST ferroelectric ceramics, no variation of transition temperature by conventional sintering and microwave sintering respectively. This promising technique has distinguished characteristics of energy saving, rapid processing and uniform temperature distribution throughout the samples.