Dielectric porcelain composition and dielectric resonator...

Details Dielectric porcelain composition and dielectric resonator... Dielectric porcelain composition and dielectric resonator...

2002-01-07

2003-05-27

Brunsman, David (Department: 1755)

Compositions: ceramic

Ceramic compositions

Titanate, zirconate, stannate, niobate, or tantalate or...

C333S219100

Reexamination Certificate

active

06569796

ABSTRACT:

This application is a 371 of PCT/JP01/00636 filed Jan. 31, 2001.
TECHNICAL FIELD
The present invention relates to a dielectric ceramic composition of excellent dielectric characteristics in a high-frequency region, particularly such a composition exhibiting a high unloaded quality factor (hereinafter referred to as “Q
u
”) and a small variation thereof, and to a dielectric resonator formed of the composition. The dielectric ceramic composition of the present invention can be used in dielectric filters, multilayer circuit boards, etc. for use in a high-frequency region.
BACKGROUND ART
Compositions represented by BaO—ZnO—Ta
2
O
5
are known to be dielectric ceramic compositions which can be used in a high-frequency region. Such dielectric ceramic compositions for use in a high-frequency region must satisfy the following requirements:
(1) a high dielectric constant (hereinafter referred to as “∈
r
”)
(2) a small absolute value of the temperature coefficient (hereinafter referred to as “&tgr;
f
”) of resonance frequency (hereinafter referred to as “f
0
”); and
(3) a high Q
u
in a high-frequency region.
The BaO—ZnO—Ta
2
O
5
dielectric ceramic compositions are oxides represented by the compositional formula of Ba(Zn
⅓
Ta
⅔
)O
3
and have a complex perovskite-type crystal structure. These oxides are generally referred to as BZT. The BZT dielectric ceramic compositions exhibit excellent dielectric characteristics, such as a high Q
u
. However, in recent years, there is a demand for a dielectric ceramic composition having a higher Q
u
, since the frequency region where such dielectric ceramic compositions are used has become higher; i.e., from the microwave region to the sub-millimeter region.
Publication of Unexamined Patent Application No. Hei 11-71173 discloses that a dielectric ceramic composition of more excellent dielectric characteristics can be obtained by incorporating a K component and a Ta component into an oxide represented by the compositional formula of Ba(Zn
⅓
Ta
⅔
)O
3
. Although incorporation of these specific components attains enhancement of dielectric characteristics, uniform Q
u
cannot always be attained, and variation in Q
u
may occur. Thus, provision of a dielectric ceramic composition exhibiting a smaller variation in dielectric characteristics is desired.
The present invention has been accomplished in order to solve the aforementioned problems, and an object of the invention is to provide a dielectric ceramic composition capable of attaining a high Q
u
without variation, by means of employing specific proportions by amount of elements in the predominant component formed of an oxide containing Ba, Zn, and Ta and by limiting the ratio by amount of K component to Ta component other than the predominant component and the ratio by weight of K to Ta. Another object of the invention is to provide a dielectric resonator formed of the dielectric ceramic composition.
DISCLOSURE OF THE INVENTION
The dielectric ceramic composition of the present invention contains Ba, Zn, and Ta, and is characterized by comprising 100 parts by weight of a predominant component represented by xBaO—yZnO—(½)zTa
2
O
5
(x, y, and z represent compositional proportions by mol and satisfy x+y+z=1), wherein x, y, and z fall within a quadrilateral region formed by connecting points A (x=0.503, y=0.152, z=0.345), B (x=0.497, y=0.158, z=0.345), C (x=0.503, y=0.162, z=0.335), and D (x=0.497, y=0.168, z=0.335) (sides AB, BD, DC, and CA being included) as shown in
FIG. 1
; 0.2-1.6 parts by weight K as reduced to K
2
O; and 0.7-8 parts by weight Ta as reduced to Ta
2
O
5
, wherein the ratio by weight of K to Ta falls within the range of 0.185-0.4.
The dielectric resonator of the present invention is characterized by being formed of the above-described dielectric ceramic composition of the present invention.
In the dielectric ceramic composition of the present invention, the aforementioned “xBaO—yZnO—(½)zTa
2
O
5
” serving as the predominant component is an oxide having a complex perovskite-type crystal structure. Some portion of Ba atoms are substituted by K, and the perovskite-type crystal structure is thought to be maintained.
In the predominant component, when any of x, y, and z is in excess of the upper limit or less than the lower limit, variation in Q
u
becomes large, even though excellent ∈
r
and &tgr;
f
and a high average Q
u
are obtained. Thus, a dielectric ceramic composition of dielectric characteristics with small variations cannot be produced. When at least two of x, y, and z are in excess of the upper limits or less than the lower limits, the average Q
u
is prone to decrease and variation in Q
u
becomes large, even through ∈
r
and &tgr;
f
do not decrease. Preferably, by controlling x, y, and z so as to fall within a quadrilateral region formed by connecting points A′ (x=0.503, y=0.154, z=0.343), B′ (x=0.497, y=0.160, z=0.343), C′ (x=0.503, y=0.161, z=0.336), and D′ (x=0.497, y=0.167, z=0.336) (sides A′B′, B′D′, D′C′, and C′A′ being included), excellent ∈
r
and &tgr;
f
can be maintained, and the average Q
u
can be further increased with further decreased variation, to thereby provide a dielectric ceramic composition of dielectric characteristics with small variations.
When the amounts of “K” and “Ta” incorporated in addition to the predominant component are less than the above-described lower limits as reduced to K
2
O and Ta
2
O
5
, respectively, particularly when the amount of K is less than the lower limit, based on 100 parts by weight of the aforementioned predominant component, the resultant composition is difficult to sinter, and in some cases, sintered products cannot be yielded. When the amounts of K and Ta are in excess of the upper limits, Q
u
greatly decreases, and variation in Q
u
increases.
When the ratio by weight of K to Ta is in excess of the upper limit or less than the lower limit, Q
u
greatly decreases, and variation in Q
u
further increases. By controlling the ratio by weight of K to Ta preferably to 0.25-0.35, more preferably 0.25-0.30, excellent ∈
r
and &tgr;
f
can be maintained, and the average Q
u
can be further increased with further decreased variation, to thereby provide a dielectric ceramic composition of dielectric characteristics with small variations.
K and Ta other than Ta contained in the predominant component form an oxide having a perovskite-mixture-type crystal structure represented by K
p
TaO
q
. In K
p
TaO
q
, K is considered to occupy the Ba site of the predominant component, and Ta is considered to occupy the Zn site or Ta site of the predominant component. The dielectric ceramic composition of the present invention has a perovskite-type crystal structure formed from the predominant component and the perovskite-type structure of K
p
TaO
q
partially occupying the predominant component, and the entire perovskite-type crystal structure is considered to be a complex perovskite-type crystal structure. In the predominant component, atoms of at least one of Zn and Ta may be substituted to some extent by an element such as Mg, Zr, Ga, Ni, Nb, Sn, or a rare earth metal element; e.g., Y. These elements are readily substituted by Zn or Ta, maintain the perovskite-type crystal structure, and do not impair excellent dielectric characteristics. In the case in which some portion of Ba atoms are substituted by Sr, &tgr;
f
can be modified while the Q
u
value is maintained.
The dielectric ceramic composition of the present invention can be produced by mixing together oxides of Ba, Zn, Ta, and K or compounds other than the oxides of Ba, Zn, Ta, and K, which compounds yield corresponding oxides by heating; shaping the resultant mixture; and firing at 1300-1700° C. In addition to the aforementioned oxides of essential metallic

Affiliated with

Also associated with

Rating

Dielectric porcelain composition and dielectric resonator... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Dielectric porcelain composition and dielectric resonator..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dielectric porcelain composition and dielectric resonator... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3073006