Fabrication and Electrical Properties of High Tc $A_{2}B_{2}O_{7}$ Piezoelectric Ceramics Using the Powders Prepared by the Molten Salt Synthesis Method

용융염합성법에 의한 $A_{2}B_{2}O_{7}$ 고온압전세라믹스의 제작과 전기적특성

Polycrystalline $Sr_{2}(Ta_{1-x}Nbx)_{2}O_{7}$ and $La_{2}Ti_{2}O_{7}$ ceramics having very high Curie temperatures were synthesized by the conventional oxide mixing method (CON) and the molten salt synthesis method (MSS). Physical characteristics and phase relationship of calcined powders, as well as the sintering behavior, the grain-orientation and dielectric properties of sintered ceramics were investigated as a function of composition and firing temperature. The single $A_{2}B_{2}O_{7}$ phase was synthesized by using the MSS method at 100 - $150^{\circ}C$ lower temperature compared to the CON method. As Nb content increased in $Sr_{2}(Ta_{1-x}Nbx)_{2}O_{7}$ ceramics, the Curie temperature and the dielectric constant at Curie temperature were raised, and the sintering behavior and the degree of grain-orientation were also improved at the same time. The use of MSS-derived powders made it possible to lower the sintering temperature and to improve the dielectric properties of the sintering samples. However, the piezoelectric properties as well as the grain-orientation were not improved any further by the MSS route.

높은 큐리온도를 가진 다결정 세라믹스 $Sr_{2}(Ta_{1-x}Nbx)_{2}O_{7}$ 및 $La_{2}Ti_{2}O_{7}$을 고상반응법과 용융염합성법으로 제조하고 조성과 하소 및 소결조건에 따른 분말특성, 상구조, 소결특성, 입자배향도 및 전기적 특성을 조사하였다. 용융염합성법에 의해 합성된 하소분말의 단일상은 고상반응법에 의한 것보다 100 - $150^{\circ}C$ 낮은 하소온도에서 나타났다. 한편 $Sr_{2}(Ta_{1-x}Nbx)_{2}O_{7}$ 소결체에서 Nb의 조성이 커질수록 입자배향도가 커지고 소결성 및 고온에서의 유전특성이 좋아졌다. 또 용융염합성법으로 $A_{2}B_{2}O_{7}$ 세라믹스를 제조할 경우 고상반응법에 비해 소결온도를 낮출 수 있고 비유전율도 다소 높일 수 있으나 압전특성이나 입자배향도는 향상되지 않았다.