• The Korean Journal of Ceramics
• /
• 제5권2호
• /
• pp.189-194
• /
• 1999

Crystallization of glasses in the system (Ca, Sr, Ba)$O-Al_2O_3-B_2O_3-SiO_2-TiO_2$ and dielectric properties of crystallized glasses were investigated. As increasing B2O3 content and decreasing SiO2 content in the glass, the major crystalline phase changed from $(Sr, Ba)_2TiSi_2O_8$ to (Ca, Sr, Ba)TiO3, the dielectric constant of crystallized glasses increased and the Temperature Coefficient of Capacitance (TCC) changed to negative. The dielectric constant and TCC was estimated for (Sr, Ba)2TiSi2O8 phase as 18 and -440 $ppm/^{\circ}C$, respectively and for (Ca, Sr, Ba)TiO3 phase as 307 and -1900 $ppm/^{\circ}C$, respectively. The dielectric properties of (Ca, Sr, Ba)TiO3 phase (in this study) were similar to those of (Ca, Ba) TiO_3 solid-solution^12)$, but $(Sr, Ba)_2TiSi_2O_8$ phase (in this study) and $Sr_2TiSi_2O_\;8^4$ showed the different properties.

• 한국전기전자재료학회논문지
• /
• 제19권5호
• /
• pp.422-426
• /
• 2006

[ $Sr_xCa_{(1-x)}TiO_3$ ] red phosphors doped with Pr(0.13 mol%) and Al(0.23 mol%) were synthesized by solid state reaction method. Change of crystal structure occurred in $Sr_xCa_{(1-x)}TiO_3:Pr,Al$ phosphors with increasing value of x. Green and red luminescence were observed from $SrTiO_3:Pr,Al$ phosphors at low temperature. However, only red luminescence in the case of $CaTiO_3:Pr,Al$ phosphors was measured at low temperature. The main cause of green luminescence was explained by the bandgap reduction.

• 대한전기학회논문지:전기물성ㆍ응용부문C
• /
• 제55권7호
• /
• pp.344-348
• /
• 2006

The effect of x on microwave dielectric properties of the $(1-x)Mg_4Ta_2O_9-x(TiO_2,\;CaTiO_3,\;SrTiO_3)$ ceramics for microwave components were investigated. All spcecimens prepared by the conventional mixed oxied method and sintered at $1450^{\circ}C$. Microwave dielectric properties of the $(1-x)Mg_4Ta_2O_9-xTiO_2$ ceramics were influenced by $MgTi_2O_5$ phase. Also the microwave dielectric properties of the $(1-x)Mg_4Ta_2O_9-x(TiO_2,\;CaTiO_3,\;SrTiO_3)$ ceramics were dominated with an addition of $CaTiO_3\;and\;SrTiO_3$. The dielectric constant $(\varepsilon_r)$, quality factor $(Q{\times}f_r)$ and temperature coefficient of the resonant frequency $(TCRF,\;\tau_f)$ of the $(1-x)Mg_4Ta_2O_9-x(TiO_2,\;CaTiO_3,\;SrTiO_3)$ ceramics were $12.96\sim70.98,\;5,132\sim186,410GHZ$ and $-35.82\sim+75.96ppm/^{\circ}C$, respectively, and depend on x and addition materials.

• 한국세라믹학회지
• /
• 제43권5호
• /
• pp.284-292
• /
• 2006

$MgTiO_3{\cdot}CaTiO_3{\cdot}SrTiO_3$ system ceramics (MCST) were synthesized to study the effect of Ca addition amount and Sr substitution on temperature coefficient of resonance sequency. Temperature coefficient of resonance frequency was slightly increased by small amount ($i.e.{\sim}5%$) of Sr substitution. In case of 50% to 75% addition amount of $MgTiO_3$, decrease of quality factor was not observed with increasing dielectric constant.

• 한국재료학회지
• /
• 제2권4호
• /
• pp.248-256
• /
• 1992

본 논문에서는 ATi$O_3$(A=Ca, Sr, Ba) 조성을 갖는 단순 페롭스카이트 구조에서 생성되는 격자결함 구조에 대하여 고찰하였다. 페롭스카이트 구조는 고충전밀도를 갖기 때문에 프렌클 결함은 고려되지 않았다. 쇼트키결함이나, 고유전자결함도 자연적으로 포함된 억셉타 불순물 농도에 비하면 무시할 정도로 적은 양이다. 실제적으로 전기적 특성에 영향을 주는 것은 전하적 결함을 발생하는 aliovalent 불순물이다. 삼성분계이기 때문에 양이온간의 비화학양론이 발생하며 BaTi$O_3$나 SrTi$O_3$에서 수백 ppm이내의 AO나 Ti$O_2$의 용해도가 관찰되나, CaTi$O_3$에서는 상당량의 CaO와 $TiO_2의$ 용해가 가능하다.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2002년도 하계학술대회 논문집 Vol.3 No.2
• /
• pp.597-600
• /
• 2002

Electrical properties of $\{(Sr_xCa_{1-x})_{0.95-y-z}Bi_2Pb_{0.05+y}\})Ti_{1.02}O_3$ ceramic were studied as a function of Sr/Ca ratio and Bi, Pb contents. Dielectric properties of specimens with different x, y, z values were explained in terms of ionic polarizability with Molecular Additionally Rules and Clausius-Mosotti equation. For the composition of $\{(Sr_{0.62}Ca_{0.38})_{0.90}Bi_{0.01}Pb_{0.09}\})Ti_{1.02}O_3$ and $\{(Sr_{0.62}Ca_{0.38})_{0.905}Bi_{0.015}Pb_{0.08}\})Ti_{1.02}O_3$, dielectric constant$({\varepsilon}_r)$, quality factor(Q) and temperature coefficient(TC) were 389, 3048, -1490 and 394, 1869, -1340 at 1MHz, respectively.

• 한국세라믹학회지
• /
• 제34권2호
• /
• pp.123-130
• /
• 1997

본 연구에서는 유전상수가 크고, 유전체 손실이 적으며, 사용온도 범위에서 정전용량 변화율(TCC : tem-perature coefficient of capacitance)이 작고, 고압에 견딜 수 있는 재료를 개발하기 위하여 중고압용 capacitance의 기본재료로써 (Sr.Pb.Ca)TiO3-xBi2O3.3TiO2 계에서 Bi2O3.3TiO2의 mol.%를 5, 6, 7, 8, 9 mol.%로 변화시켰으며, 그 결과 고용한계 함량이 6mol.%이며, 6mol.%이상에서는 침상구조의 증가에 기인하여 유전율이 다시 감소하는 경향을 보였다. dopant로써 SiO2, Nb2O3, MnO2를 선정하여 첨가한 결과, MnO2를 첨가한 것이 유전성질이 가장 우수하였으며, MnO2의 함량이 0, 0.15, 0.3, 0.45 wt.% 증가함에 따라서 유전율의 감소와 동시에, TOC특성의 급격한 향상을 가져왔다.

• 한국세라믹학회지
• /
• 제38권2호
• /
• pp.107-111
• /
• 2001

Sr$_{(1-x)}$Ca$_{x}$TiO$_3$: Pr$^{3+}$ , Ga$^{3+}$ (0$\leq$x$\leq$1) 형광체의 여기 및 발광 스펙트럼과 분광 반사율을 조사하여 발광 메커니즘을 규명하고자 하였다. 발광 스펙트럼에서는 611~614nm 사이에서 peak을 가지는 하나의 적색 발광 밴드가 관찰되었으며, 조성에 따라 발광밴드의 모양이 달랐다. 이는 조성에 따른 모체의 결정 구조 변화 때문으로 생각된다. 여기 스펙트럼 끝단과 분광 반사율 스펙트럼의 흡수단은 서로 일치하였으며, 이 결과로부터 모체에 흡수된 에너지가 Pr$^{3+}$ 에 전달되어 적색광을 방출하는 것이 주된 메커니즘으로 생각된다. 한편 120$0^{\circ}C$에서 4시간동안 열처리하여 합성한 Sr$_{0.4}$Ca$_{0.6}$TiO$_3$:(0.1 mol%)Pr$^{3+}$ , (0.2 mol%)Ga$^{3+}$ 는 우수한 색순도와 휘도를 나타내었다.다.

• 한국세라믹학회지
• /
• 제28권9호
• /
• pp.689-695
• /
• 1991

Dielectric properties of Ba1-$\chi$Sr$\chi$Ti1-yCayO3-y ceramics, where Sr and Ca were doped to Ba-site and Ti-site within the range of 0 x 0.24 and 0 y 0.05, respectively, were investigated. The substitution of Ca for Ti, which maintained the high resistivity of these formulations after sintering in a reducing atmosphere, was confirmed. Ca addition decreased the tetragonality c/a, increased the unit cell volume, and lowered Curie temperature, which were attributed to the occupancy of Ca2+ ions on Ti-sites. The lowering of Curie temperature by Ca addition was affected by the substitution of Sr for Ba-site; within 2 mol% of Ca, Curie temperature was lowered at a rate of 2$0^{\circ}C$ and 16$^{\circ}C$ per mol% of Ca at x=0 and x=0.08, respectively. Whereas the resistivity of the formulations without Ca was reduced to 107 {{{{ OMEGA }}cm, when sintered at low oxygen partial pressure of 10-9 MPa, the resistivity value higher than 1011 {{{{ OMEGA }}cm was maintained for the formulations containing Ca more than 0.5 mol%. Dielectric loss factor, tan$\delta$, was about 1% for most formulations.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2009년도 하계학술대회 논문집
• /
• pp.180-181
• /
• 2009

$(Ba_{0.6},Sr_{0.3}Ca_{0.1})TiO_3$ powders, which were prepared by sol-gel method using a solution of Ba-acetate, Sr-acetate and Ca-acetate and Ti iso-propoxide, $(Ba_{0.6},Sr_{0.3}Ca_{0.1})TiO_3$ array thick films doped with 0.1 mol% $MnCO_3$ and $Yb_2O_3$ (0.1~0.7 mol%) were fabricated by the screen printing method on the alumina substrate. And the structural and electrical properties as a function of $Yb_2O_3$ amount were investigated. The thickness of all (Ba,Sr,Ca)$TiO_3$ thick films was approximately 60mm. The Curie temperature of doped with 0.1 mol% $Yb_2O_3$ specimen was $45^{\circ}C$, and the dielectric constant and at this temperature was 1062.