As a result, even if the composition described in Patent Document 2 is used, it is by no means possible to attain a piezoelectric part that can resist the reflow heating treatment. Besides, since the composition is used as the dielectric, the Curie point Tc of the composition is as low as around room temperature. As a result, satisfactory piezoelectric properties cannot be obtained and it is difficult to secure the desired piezoelectricity even if the composition is applied to a piezoelectric part. Due to this, the mixture molar ratio of Ti in B site is as low as 0.7 or lower. The composition described in Patent Document 2 can be fired at the low temperature but the ceramic composition is developed for use as a dielectric. Due to this, each of these compositions possibly cannot resist a reflow heating treatment of the lead-free solder.įurthermore, each of the compositions described in Patent Document 1 contains Co, a scarce metal, as an essential constituent element and, therefore, it is possibly difficult to reliably acquire ceramic raw material. The Curie points Tc of most of the compositions described in Patent Document 1 are around 200° C. Due to this, the Curie point Tc of the piezoelectric part is required to be high enough to resist a reflow heating treatment on the lead-free solder. If the temperature exceeds the Curie point Tc, polarization of the piezoelectric part vanishes and the piezoelectric part does not exhibit piezoelectricity. This requires a piezoelectric part obtained using the lead-free solder to have higher heat resistance.
However, the melting temperature of the lead-free solder is normally higher than that of the lead-containing solder. In recent years, a demand for changing from lead solder to a lead-free solder has arisen from environmental and other viewpoints. Meanwhile, it is prevailing practice to mount a piezoelectric part on a board by performing a solder reflow heating treatment. 7-12975 DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention Patent Document 2: Japanese Examined Patent Publication No. Patent Document 1: Japanese Unexamined Patent Publication No. can be obtained by setting a, b, x, y and z in the general formula to fall within predetermined ranges, respectively. represented by a general formula of (Pb 1-x-圜a xSr y)O 2+a+b] (where x+y+z=1, Me is at least one member selected from among the group consisting of Ca, Sr and Ba), although this composition is a dielectric ceramic composition (Patent Document 2).Īccording to Patent Document 2, a high-dielectric-constant dielectric ceramic composition that can be fired at a low temperature equal to or lower than 1100° C. A piezoelectric ceramic composition comprising a main component having a Curie point of at least 300° C.
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