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INFLUENCE OF SYNTHESIS TEMPERATURE AND SR SUBSTITUTION ON ABSORPTION CHARACTERISTICS OF BA SYSTEM MICROWAVE DIELECTRICS Kang M.G.1, Jong Ch.J.2
1Kang Myong Guk - Candidate of Geological Science, Teacher;
2Jong Chol Jin - Associate Professor, Candidate of Geological Science, Teacher, DEPARTMENT MINERAL MATERIAL, FACULTY OF GEOLOGICAL EXPLORATION, HWANGBUK UNIVERSITY, SARIWON, DPR OF KOREA
Abstract: microwave dielectric materials are widely used as radar absorbers and chip materials as well as satellite communicators and portable telephones. The article discusses the influence of Bax _ x5rx7 i 03 system on the microwave absorption characteristics in the 9 ~ 10GHz band. In the experiment was set the Sr substitution rate and carried out the X-ray structure analysis. Also examined absorption characteristics of materials according to synthesis temperature and investigated the microwave absorption characteristics according to content Sr of system.
Keywords: influence, temperature, Sr, Ba, microwave dielectrics.
The material of microwave dielectrics is used widely to satellites, portable telephones, as well as radar absorption and screening materials.
In this paper the influence of system on the microwave absorption
characteristics in the 9 ~ 10GHz band was experimentally confirmed.
1. Experimental method
In the experiment, the Sr substitution rate of system was set to
x = 0.1 ~ 0.4.
The basic materials were weighed to the stoichiometric ratio using Ba (99%), SrC (99.5 %) and Ti02 (99 %). The basis weight of the sample was 1 0 _ 3 g of precision by using the electric balance "FX - 300" and the weighed sample was carried out to mixing and grinding with a wet ball mill for 30 h.
To evaluate the reasonable ratio of ball: sample: distilled water, the blending ratio according to mixing ratio was experimentally investigated. In general, it is common to making mixable ratio in volumetric: samples: distilled water = 1: 1: 0.6 ~ 0.8 in the dielectric ceramics making process, when the mixing ratio is 1: 1: 1 ~ 1: 1: 1: 2, the mix -milling ratio was increased.
Then, the rotational frequency of ball - mill was 130 - 160 r/ min by the diameter of the ball-column.
The mixed and pulverized samples were dried at a temperature of 100 °C for 24 hours until they became constant weight, pulverized with a mortar, sieving of 100 ^m sieve, then was poured into the column the 7 wt % distilled water, and was formed into same sieve again. After were synthesized and put into alumina crucible the composite sample of size 9 = 40 mm on the pressure of 50 MPa.
Synthesizing increase to final synthesis temperature on the speed v = 100°C/h and carried out to method keeping it. Synthesis conditions were maintained between 900 -1200°C for 3h and cooling naturally. The composite sample was milled again into ball -mill, sieving, and made the specimens with a thickness of 2 mm.
2. Results and discussion
First, the X-ray structure analysis of the B ax _xSrxTi0 3 system (x = 0.27) carried out. X-ray diffraction analysis (XRD - Rigaku) was carried out at 2 0 = 18 - 60°C using CuKa and Ni filter.
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The X-ray diffractive graphic shows that this system has a tetragonal structure at room temperature and that the B a i _ x S rxTi 0 3 phase was precisely formed at 1100°C.
Fig. 1. X-ray diffractive graphic of Ba0 ^73 Sr0 ^ 2 7 Ti 0 3
According to the literature [1, 2, 3], the BT material is formed with solid solution at more than 1200°C and has a tetragonal structure, but solid solution material is formed at 1100°C in the experiment. This is because the sintering property of the material is improved due to the effect of Sr, which is a substitute.
In the experiment, first, absorption characteristics of materials according to synthesis temperature were examined.
Figure 2 shows the standing wave number change of the B ax _xSrxTi03 (x = 0.27) material at 9.4 GHz according to the synthesis temperature. As see in figure, the standing wave coefficient is minimized at around 1100°C, where the BST dielectric material is fully formed. This shows that the temperature at which the BST solid solution is completely formed is near 1100°C, and the microwave absorption characteristic of the material is increased.
Secondly, the microwave absorption characteristics according to content Sr of system were investigated. Characteristic measurements were carried out at 9.4 GHz for ® = 40 x 2 mm specimens.
Fig. 2. The steady-state logarithmic change according to the synthesis temperature of Ba ± _ ^-Sr^T i 0 3
(x = 0.27)
The change of the standing wave coefficient S according to the content of Sr is shown in figure 3.
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Fig. 3. Change of the standing wave coefficient S according to the content of Sr
As shown in the figure, the standing wave coefficient decreases to 0.27 mol % depending on the amount of Sr and increases above that.
The change of the standing wave coefficient S depending on the amount of Sr can be considered to be caused by the ion radius difference of the substituted atoms. Because of the ion radius of Sr2+ is 0.144 nm, and of Ba2+ is 0.161 nm, when the proper amount is entered, this can considerate which the lattice deformation is caused to increase the loss. Therefore the BST has a dielectric constant of 45 and a standing wave coefficient s = 12 when the contents of substituted Sr is 0.27 mol %, and has a reflection loss of about 1.4 dB. Conclusion
1) It was found that the proper plastic conditions of the BST system affecting the microwave absorption characteristics are 1100°C and 3 h.
2) The optimal replacement amount of Sr, which affects the enhancement of the absorption characteristics of the BST system, is 0.27 mol %, and the dielectric constant is 45 and the standing wave coefficient is s = 12 at 9 to 10 GHz.
References
1. Sebastian M.T. et al. Journ. Euro. Cera. Soc. 27 (2007). 2827-2823.
2. Ioachim A. et al. Thin solid Films. V. 27 (2007). 2600.
3. Shanhua Wu et al. Journ. Euro. Cera. Soc. 23 (2003). 2565-2568.
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