• Journal of the Korean Ceramic Society
• /
• v.35 no.11
• /
• pp.1203-1211
• /
• 1998

The microwave sintered BaTiO3 samples were obtained by using the microwave sintering device which can precisely control the sintering temperature and the sinter time by using IR optical thermometer and PID temperature controller. During microwave sintering the internal temperature of samples were mesur-ed by the optical fiber thermometer to compare the sintering behaviors between microwave- and con-ventionally sintered ones. The former showed the faster rate of grain growth with sintering time and the larger grain size than the latter. Also they showed the similar pattern of dielectric properties with tem-perature changes from 2$0^{\circ}C$ to 16$0^{\circ}C$.

• Electrical & Electronic Materials
• /
• v.10 no.3
• /
• pp.274-283
• /
• 1997

These days, according to surprising development of communication enterprises, every soft of devices is getting smaller and cheaper. Among these Devices, microwave dielectric ceramics are studied and progressed briskly as the materials of dielectric resonator. Dielectric properties of BaO-S $M_{2}$ $O_{3}$-Ti $O_{2}$, one of the BaO Lnsub 2/ $O_{3}$-Ti $O_{2}$ (Ln=La, Sm, Nd, Pr…) system, synthesized by solid-reaction and coprecipitation method were investigated. Disk-type samples were sintered at 1250-1400.deg. C for 2hrs. As a result, single phase was not synthesized in both method. First created the second phase of S $M_{2}$ $Ti_{2}$ $O_{7}$, and then the last phase of $Ba_{3.75}$S $m_{9.5}$ $Ti_{18}$ $O_{54}$, Ti $O_{2}$, and $Ba_{2}$ $Ti_{9}$ $O_{20}$. When the sample was sintered at 1280.deg. C (in solid reaction method) and at 1310.deg. C (in coprecipitation method), it obtained highest dielectric constant (72.96 and 71.70, respectively) and high Q value. Above that temperature, dielectric constant and Q value decreased because of lattice defect according to oxygen vacancies........

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.49 no.5
• /
• pp.294-298
• /
• 2000

The $MgTiO_3\; and \;$0.9MgTiO_3-0.1SrTiO_3$ ceramics were fabricated by the conventional mixed-oxide method. The sintering temperature and time were $1300^{\circ}C~1600^{\circ}C$, 2hr., respectively. The structural and microwave dielectric properties were investigated with sintering temperature and the application for the satellite communication microwave dielectric resonator was investigated. The coexistence of cubic $SrTiO_3$ and hexagonal TEX>$MgTiO_3$ structures in $0.9MgTiO_3-0.1SrTiO_3$ ceramics were found from X-ray diffraction patterns. In the case of $MgTiO_3$ ceramics, sphere phase and needle-like phase were coexisted. The $0.9MgTiO_3-0.1SrTiO_3$ ceramics observed sphere phase. The dielectric constants and temperature coefficient of resonant $frequency(\tauf)$ were increased with addition of $SrTiO_3$ but the quality factor was decreased. The dielectric constant, quality factor and $\tau$f of the;$0.9MgTiO_3-0.1SrTiO_3$ ceramics were 22.61, 10.928(at 1GHz) and $+50.26ppm/^{\circ}C$, respectively.

• Journal of the Korean Ceramic Society
• /
• v.34 no.4
• /
• pp.368-372
• /
• 1997

The microwave dielectric properties of (1-x)La2/3TiO3-xLaAlO3 system in which LaAlO3 having $\varepsilon$r$\geq$90 and positive $\tau$f was investigated. The crystal system of (1-x)La2/3TiO3-xLaAlO3 was pseudo-cubic in the range of 0.1$\leq$x$\leq$0.07. Its lattice constant increased with increasing x in spite that the amount of LaAlO3 containing of smaller Al(0.57 $\AA$) ion than Ti(0.64 $\AA$) increased. As the amount of LaAlO3 increased from x=0.1 to 0.9, the relative dielectric constant ($\varepsilon$r) decreased from 50 to 23 and the temperature coefficient of resonant frequency($\tau$f) decreased from +84 to -50. On the other hand, the value of Q.f0 reached a maximum (148,000 at 7 GHz) at x=0.7, where a rapid increase in the peak intensity of XRD occured, and further increased after prolonged sintering. The microwave dielectric properties of $\varepsilon$r=37, Q.f0=47,000 (at 7 GHz), and $\tau$f=-2 ppm/$^{\circ}C$ were obtained near 0.6La2/3TiO3-0.4LaAlO3 (x=0.4) composition.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.16 no.11
• /
• pp.975-978
• /
• 2003

The microwave dielectric properties and the microstructures on B $i_{0.97}$T $m_{0.03}$Nb $O_4$ doped with $V_2$ $O_{5}$ were systematically investigated. B $i_{0.97}$T $m_{0.03}$Nb $O_4$ ceramics sintered at 920-96$0^{\circ}C$ were mainly consisted of orthorhombic and triclinic phases after addition of $V_2$ $O_{5}$. The apparent density increased slightly with increasing the $V_2$ $O_{5}$ addition. The dielectric constants($\varepsilon$$_{r}$) also increased with $V_2$ $O_{5}$ addition(30-45). The Q${\times}$ $f_{0}$ values measured on B $i_{0.97}$T $m_{0.03}$Nb $O_4$ ceramics doped with $V_2$ $O_{5}$ were between 2,000 and 12,000[GHz] when the sintering temperatures were in the range of 920-960[$^{\circ}C$]. It was confirmed that the temperature coefficient of the resonant frequency($\tau$$_{f}$) can be adjusted from a positive value of +10ppm/$^{\circ}C$ to a negative value of -15ppm/$^{\circ}C$ by increasing the amount of $V_2$ $O_{5}$ Based on our experimental results, the B $i_{0.97}$T $m_{0.03}$Nb $O_4$(added $V_2$ $O_{5}$) ceramics can be applied to multilayer microwave devices at low sintering temperatures.ng temperatures.emperatures.ratures.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2002.11a
• /
• pp.350-353
• /
• 2002

The microwave dielectric properties and the microstructures on $Bi_{0.97}Nb_{0.03}O_{4}$doped with $V_{2}O_{5}$ were systematically investigated. $Bi_{0.97}Tm_{0.03}Nb_{0.03}O_{4}$ ceramics sintered at $920-960^{\circ}C$were mainly consisted of orthorhombic and triclinic phases after addition of $V_{2}O_{5}$. The apparent density increased slightly with increasing the $V_{2}O_{5}$ addition. The dielectric $constants(\varepsilon_r)$ also increased with $V_{2}O_{5}$ addition(30-45). The $Q{\times}f_0$ values measured on $Bi_{0.97}Tm_{0.03}NbO_4$ ceramics doped with $V_{2}O_{5}$ were between 2,000 and 12,000[GHz] when the sintering temperatures are in the range of $920-960[^{\circ}C]$. It was confirmed the temperature coefficient of the resonant $frequency(\tau_f)$ can be adjusted from a positive value of $+10[ppm/^{\circ}C]$ to a negative value of $-15ppm/^{\circ}C$ by increasing the amount of $V_{2}O_{5}$. Based on our experimental results, the Bi0.97Tm0.03NbO4(added V2O5) ceramics can be applied to multilayer microwave devices at low sintering temperatures.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2003.07b
• /
• pp.719-722
• /
• 2003

Ferroelectric $Pb(Zr_{1-x}Ti_x)O_3$ (PZT) films were deposited on (001) MgO single crystals using sol-gel method. Structural properties and surface morphologies of PZT films were investigated using an X-ray diffractometer and a scanning electron microscopy, respectively. The dielectric properties of PZT films were investigated with the dc bias field using interdigitated capacitors (IDC) which were fabricated on PZT films using a thick metal layer by photolithography and dry etching process. The small signal dielectric properties of PZT films were calculated by a modified conformal mapping method with low and high frequency data, such as capacitance measured by an impedance gain/phase analyzer at 100 kHz and reflection coefficient (S-parameter) measured by a HP 8510C vector network analyzer at 1 -20 GHz. The IDC on PZT films exhibited about 67% of capacitance change with an electric field of 135 kV/cm at 10 GHz. These PZT thin films can be applied to tunable microwave devices such as phase shifters, tunable resonators and tunable filters.

• Journal of the Korean Institute of Telematics and Electronics
• /
• v.27 no.10
• /
• pp.10-15
• /
• 1990

Theory and experimental results of measuring the microwave dielectric characteristics of low-loss materials by using dielectric rod resonator method are presented. The $TE_{011}$ mode resonance frequency was adapted to minimize the effect of the air gap between the rod and the conducting plates. The dielectric properties were computed from the resonance frequency, sample geometry and 3 dB bandwidth. The error of measurements was within ${\pm}3{\%}$ for dielectric constant and was within ${\pm}12{\%}$ for dielectric loss.

• Advances in materials Research
• /
• v.3 no.2
• /
• pp.105-116
• /
• 2014

The microwave dielectric properties of $CeO_2$ nanoparticles (0.5, 1.0 & 1.5wt%) doped $Mg_2TiO_4$ (MTO) ceramics have been investigated at cryogenic temperatures. The XRD patterns of the samples were refined using the full proof program reveal the inverse spinel structure without any secondary phases. The addition of $CeO_2$ nanoparticles lowered the sintering temperature with enhancement in density and grain size as compared to pure MTO ceramics. This is attributed to the higher sintering velocity of the fine particles. Further, the microwave dielectric properties of the MTO ceramics were measured at cryogenic temperatures in the temperature range of 6.5-295 K. It is observed that the loss tangent ($tan{\delta}$) of all the samples increased with temperature. However, the $CeO_2$ nanoparticles doped MTO ceramics manifested lower loss tangents as compared to the pure MTO ceramics. The loss tangents of the pure and MTO ceramics doped with 1.5 wt% of $CeO_2$ nanoparticles measured at 6.5K are found to be $6.6{\times}10^{-5}$ and $5.4{\times}10^{-5}$, respectively. The addition of $CeO_2$ nanoparticles did not cause any changes on the temperature stability of the MTO ceramics at cryogenic temperatures. On the other hand, the temperature coefficient of the permittivity increased with rise in temperature and with the wt% of $CeO_2$ nanoparticles. The obtained lower loss tangent values at cryogenic temperatures can be attributed to the decrease in both intrinsic and extrinsic losses in the MTO ceramics.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.16 no.7
• /
• pp.604-610
• /
• 2003

The effects of sintering additives such as B $i_2$ $O_3$ and $V_2$ $O_{5}$ on the microwave dielectric and sintering properties of (Z $n_1$$_{-xM}$ $g_{x}$)Ti $O_3$ system were investigated. Highly dense samples were obtained for (Z $n_{0.8}$M $g_{0.2}$)Ti $O_3$ at the sintering temperature range of 870~90$0^{\circ}C$ with B $i_2$ $O_3$ and $V_2$ $O_{5}$ additions of 〈1 wt.%, respectively. The microwave dielectric properties of (Z $n_{0.8}$M $g_{0.2}$)Ti $O_3$ with 0.45 wt.%B $i_2$ $O_3$ and 0.55 wt.% $V_2$ $O_{5}$ sintered at 90$0^{\circ}C$ were as follows : Q$\times$ $f_{o}$ = 50,800 GHz, $\varepsilon$$_{r}$ = 22, and $\tau$$_{f}$ = -53 ppm/$^{\circ}C$. In order to improve temperature coefficient of resonant frequency, Ti $O_2$ was added to the above system. The optimum amount of Ti $O_2$ was 15 moi.% when sintered at 87$0^{\circ}C$, at which we could obtain following results: Q$\times$ $f_{o}$ = 32,800 GHz, $\varepsilon$$_{r}$ = 26, and$\tau$$_{f}$ = 0 ppm/$^{\circ}C$.EX>.EX>.EX>.EX>.EX>.EX>.EX>.