• Journal of the Korean Ceramic Society
• /
• v.29 no.4
• /
• pp.259-264
• /
• 1992

The crystal structures and the bonding characteristics in $(Ba_xPb_{1-x})TiO_3$ have been investigated by X-ray diffraction analysis and infrared spectrophotometry. As $Ba^{2+}$ ion in $BaTiO_3$ were substituted by $Pb^{2+}$ ion, the structures were changed to orthorhombic from tetragonal, and also the covalent character in Ti-O bond increased, and then the dielectric constants decreased gradually. In the mixed oxide containing $Pb^{2+}$ ion more than 50%, the change-transfer energy of titanium ion increased.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.17 no.2
• /
• pp.69-74
• /
• 2007

[ $0.6Pb(Sc_{1/2}Ta_{1/2})O_3-0.4PbTiO_3$ ] (hereafter PSTT) ceramics were prepared by the molten salt synthesis (MSS) method using KCI as a flux. Formation of perovskite phase was investigated by a differential thermal analysis (DTA) and X-ray diffraction (XRD) analysis in the temperature range from $600^{\circ}C$ to $850^{\circ}C$. A 92% perovskite phase was synthesized at $750^{\circ}C$ for 2 hrs using the MSS method, while 82% perovskite phase was synthesized at $850^{\circ}C$ for 4ks using the calcining of mixed oxide (CMO) method. This result could be due to the improvement in reactivity of $Sc_2O_3$ by melting of KCI. The MSS specimen sintered at $1,100^{\circ}C$ for 4hrs showed a dielectric constant of 11,200, a remnant polarization of $13.5{\mu}C/cm^2$ and a coercive field of 10.198 kV/cm, which was discussed in view of the microstructure.

• Journal of the Korean Ceramic Society
• /
• v.38 no.2
• /
• pp.117-121
• /
• 2001

본 연구에서는 Zr $O_2$첨가가 Ba(Zn$_{1}$3/Ta$_{2}$3/) $O_3$(BZT)세라믹의 구조와 고주파 유전특성에 미치는 영향을 조사하였다. 모든 시료에서 $Ba_{5}$Ta$_4$ $O_{15}$ 이차상이 발견되었으며 Zr $O_2$의 첨가량이 증가하면 $Ba_{5}$Ta$_4$ $O_{15}$ 상의 양은 감소하였다. 반면에 Zr $O_2$의 첨가량이 1.5 mol% 이상인 시료에서는 $Ba_{0.5}$Ta $O_3$상이 발견되었다. BZT의 입자 크기는 약 1$mu extrm{m}$ 정도였지만, Zr $O_2$를 첨가하면 입자 크기가 증가하였다. SEM 및 TEM 분석에 의하여 Zr $O_2$가 첨가되면 액상이 존재하는 것을 알 수 있었으며, 이로 인하여 입자가 성장되는 것이 발견되었다. 시편의 밀도는 소량의 Zr $O_2$를 첨가하면 증가하지만 Zr $O_2$첨가량이 증가하면 감소하였다. 유전율은 모든 시료가 27에서 30 사이의 값을 가지고 있었다. 공진주파수 온도계수는 소량의 Zr $O_2$을 첨가하였을 때는 변화하지 않았지만 첨가량이 2.5 mol% 이상에서는 증가하였다. Q$\times$f 값은 Zr $O_2$을 첨가하면 증가하였고, 입자 성장이 완료되는 조성에서 최대 값을 보였다. 본 연구에서는 Zr $O_2$를 2.0 mol% 첨가하고 15$50^{\circ}C$에서 10시간 소결한 시료에서 최대의 Q$\times$f 값(164,000)을 얻을 수 있었다.다.다.

• Korean Journal of Materials Research
• /
• v.15 no.6
• /
• pp.413-418
• /
• 2005

Perovskite $Pb(Ni_{1/3}Nb_{2/3})O_3-Pb(Zr,Ti)O_3[PNN-PZT]$ ceramics were synthesized by conventional ceramic processing technique. In order to modify piezoelectric properties for sensor application in this system, NiO addition was considered to provide $Ni^{+2}$ as an acceptor, which was known to occupy with B site in the structure. The effect of NiO addition up to $8\;mol\%$ on the following piezoelectric properties as well as sintering properties was investigated. When NiO added more than $1\;mol\%$, average grain size was decreased and second phase was found to form. Moreover, the second phase caused decrease in relative dielectric constant $(\varepsilon_{33}T/\varepsilon0)$, electro-mechanical coupling factor $(k_p)$, and piezoelectric charge constant $(d_{33})$, while increasing mechanical quality factor $(Q_m)$. When $1\;mol\%$ NiO was added, density, dielectric properties and piezoelectric properties were abruptly increased.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.4 no.4
• /
• pp.341-345
• /
• 2003

ZnWO$_4$shows excellent frequency selectivity due to its high quality factor(Q${\times}$f) at microwave frequencies. However, in order to use ZnWO$_4$as multilayered wireless communication components, its other properties such as sintering temperature(105$0^{\circ}C$). $$\tau$_f$(-70ppm/$^{\circ}C$) and $$\varepsilon$_r$(15.5) should be modified. In present study, TiO$_2$and LiF were used to improve the microwave dielectric and sintering properties of ZnWO$_4$. TiO$_2$ additions to ZnWO$_4$changed $\tau$$_{f}$ from negative to positive value, and also increased $$\varepsilon$_r$, due to its high $$\tau$_f$(＋400ppm$^{\circ}C$) and $$\varepsilon$_r$(100). At 20 mol% TiO$_2$ addition, $$\tau$_f$was controlled to near zero ppm/$^{\circ}C$ with $$\varepsilon$_r$=19.4 and Q${\times}$ f=50000GHz. However, the sintering temperature was 110$0^{\circ}C$. LiF addition to the ZnWO$_4$＋TiO$_2$ mixture greatly reduced the sintering temperature from 110$0^{\circ}C$ to 85$0^{\circ}C$ due to liquid phase formation. Also LiF addition decreased the $$\tau$_f$value due to its high negative $$\tau$_f$ value. Therefore, by controlling the TiO$_2$and LiF amount. temperature stable LTCC(Low Temperature Cofired Ceramics) material with low loss in the ZnWO$_4$-TiO$_2$-LiF system could be fabricated.d.d.

• Korean Journal of Crystallography
• /
• v.17 no.1
• /
• pp.24-32
• /
• 2006

The microwave dielectric properties of $Zn_3Nb_2O_8\;with\;V_2O_5$ addition were investigated. The addition of $V_2O_5$ enhanced the sinterability of $Zn_3Nb_2O_8$, which resulted in high density of $Zn_3Nb_2O_8$ ceramic greater than 95% of the theoretical value when sintered at $900^{\circ}C$ for 4 hours. X-ray diffraction analysis of sintered $Zn_3Nb_2O_8$ ceramic showed no second phase with $V_2O_5$ addition. Dielectric permittivity(${\varepsilon}_r$) and quality factor($Q{\times}f$) varied with both density at different sintering temperature and $V_2O_5$ addition. Dielectric permittivity, quality factor and temperature coefficient($T_{cf}$) of the two mole of $V_2O_5\;added\;Zn_3Nb_2O_8$ that was sintered at $900^{\circ}C$ were 21.4, 40,000, $-54ppm/^{\circ}C$, respectively.

• Korean Journal of Materials Research
• /
• v.8 no.7
• /
• pp.659-663
• /
• 1998

The effect of Bi-substitution in $BaO.(Nd_{1-x}Bi_x)_2O_3.4TiO_2$ ceramic was studied on the formation of crystal phases, microstructure, and microwave dielectric properties. $BaO.(Nd_{1-x}Bi_x)_2O_3.4TiO_2$, solid solution (0$\leq$x$\leq$0.2) were formed by Bi-substitution into the Nd site of $BaO.(Nd_{1-x}Bi_x)_2O_3.4TiO_2$ ceramics. Average grain size increased with Bi-substitution. Dielectric constant(${\varepsilon}_r$) increased from 84 to U8, and the temperature coefficient of resonant frequency(${\tau}_f$) decreased from 44 ppm/$^{\circ}C$ to -30 ppm/$^{\circ}C$ when Bi contents increased up to x=0.2 in $BaO.(Nd_{1-x}Bi_x)_2O_3.4TiO_2$ solid solutions. $BaO.(Nd_{1-x}Bi_x)_2O_3.4TiO_2$ solid solutions with x=0.04~0.08 showed the most superior microwave dielectric properties, those are ${\varepsilon}_r$= 89-92, Q . f = 5855~6091 GHz, and (${\tau}_f$)= -7.5-7.5 ppm/$^{\circ}C$.

• Journal of the Korean Institute of Telematics and Electronics D
• /
• v.35D no.2
• /
• pp.78-85
• /
• 1998

The design method of a temperature stable bandpass filter using dielectric coaxial resonators of with two dielectric ceramics with opposite signs of temperature coefficient of dielectric constant (${\tau}_{\epsilon}$) to compensate for each other in this method. $MgTiO_3$(${\tau}_{\epsilon}$=+99 ppm/${\circ}C$) as a positive ${\tau}_{\epsilon}$ material and Ba($Zn_{1/3}Nb_{2/3}$)$O_3$(${\tau}_{\epsilon}$=-77ppm/${\circ}C$) as a negative material were selected. The length of a SIR for the temperature stability was calculated according to the design method and the susceptance slope parameter of the SIR was obtained. A temperature stable bandpass filter using dielectric SIR's was designed, simulated and fabricated. The center frequency of this filter was 915 MHz and the pass bandwidth was 20 MHz. Temperature properties of this bandpass filter by simulations were compared with the measured results of the bandpass filter fabricated.

• Journal of the Korean Ceramic Society
• /
• v.37 no.3
• /
• pp.256-262
• /
• 2000

The dielectric properties of complex perovskite ($Pb_{1-x}Ca_{x}$)($Fe_{0.5}Ta_{0.5}$)$O_{3}$ with >($0.5{\le}x{\ge}0.65$ were investigated at microwave frequencies. Dilectric constant decreased with increasing Ca content, and was directly proportional to the cube of average ionic ra야 of A-site. For the specimen of x=0.6 sintered at $1250^{\circ}C$ for 3 h in air, dielectric constant (k) of 63, QF of 11000 GHz, and the temperature coefficient of resonant frequency(TCF) of -14ppm/$^{\circ}C$ were obtained. As Ca content increased, TCF of the specimen negatively increased due to the reduction of the tolerance factor(t). Changes in intrinsic loss with varying Ca content was investigated by the infrared reflectivity spectra ranging 50 to 4000 $cm^{-1}$, which were calculated by the Kramers-Kronig analysis and classical oscillator model. The relative tendency of microwave dielectric properties of the ($Pb_{1-x}Ca_{x}$)($Fe_{0.5}Ta_{0.5}$)$O_{3}$ specimens calculated from the reflectivity data were in good agreement with the results by the post resonant method.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.17 no.11
• /
• pp.1178-1185
• /
• 2004

In the atmosphere of $N_2$ gas, BaZ $r_{0.08}$ $Ti_{0.92}$ $O_3$ polycrystal was grown by floating zone technique using BaZ $r_{0.08}$ $Ti_{0.92}$ $O_3$ ceramics as a feed and SrTi $O_3$(1l0) single cystal as a seed. The dielectric constant and loss at 10 kHz, 100 kHz, and 1 MHz for the as-grown sample were measured as a function of temperature in the temperature range between -10$0^{\circ}C$ and 150 $^{\circ}C$ to find a dielectric peak with frequency dispersion at Curie point. The hysteresis loop showed that the grown sample had very small polarization which was 0-0.01 $\mu$C/$\textrm{cm}^2$ for the applied dc-electric fields from -7 kV/cm to +7 kV/cm. However, the normal hysteresis loop was appeared after oxygen annealing. The electric-field dependence of the dielectric constant for both the as-grown and the post-annealed samples was studied by measuring the dielectric constants as a function of the biased-electric fields and their tunability was figured out from it at room temperature(27 $^{\circ}C$) and cryotemperature( -73$^{\circ}C$). Tunability for the as-grown sample was 51 % and the figure of merit 20.4 at 10kHz with the biased electric-field of 12 kV/cm. The tunability for the grown sample may be increased up to 80 % if the electric field of 25 kV/cm is applied. Tunability for the post-annealed sample was 41 % and the figure of merit 10.3 at 10 kHz with the biased electric-field of 12 kV /cm. Post-annealing improved the crystallinity of the as-grown sample but decreased its tunability.ability.