본 연구에서는 Bi(Na,K)TiO₃의 압전물성, 전기기계 결합계수에 미치는 첨가물의 영향을 밝히고자 (Bi0.5Na0.5TiO3-Bi_(0.5)Na_(0.5)TiO₃ : 이하 _(x)BNT-_(1-x)BKT)를 기본 조성으로 여기에 천이금속화합물(A, B), SrTiO₃ 등의 여러 가지 첨가물을 첨가 및 치환하여 그에 의한 결정구조, 전기기계 결합계수의 변화와 미세구조 변화를 조사하였다.
BNT_(x)-BKT_((1-x))(x=0.82~0.88) 조성에서 x=0.86의 유전율과 Tc가 가장높았으며 상온에서의 유전율은 471, Tc는 390℃이며, _((1-x))BNKT-_(x)SrTiO₃(x=0.01~0.07) 조성은 x=0.03 SrTiO₃가 치환되었을때 유전율과 Tc는 837, 280℃이다. 이와같이 ST의 첨가함으로서 유전율은 증가하고, Tc는 첨가량이 증가할수록 낮아지는 경향을 보였다.
_(x)BNT-_((1-x))BKT(x=0.86) 조성의 기계적 품질계수인 Q_(m) 과 전기기계결합계수 k_(p)는 각각 205, 30%이다. 여기에 천이금속화합물(A, B)을 1wt% 첨가하게 되면 Q_(m) and k_(p) 는 400~500, 31~32%로 증가하게된다. 전기기계결합계수는 비슷하나 기계적 품질계수가 2배이상 증가하는 것으로 나타난다.
Alternative Abstract
In this research, the structure-processing-properties relations of BNT and solid solutions of BNT-BKT with Ni, Mn, ST were assessed. These modified BNT-BKT compositions were formulated by the conventional mixed oxide method, following optimized powder processing, specimen fabrication, and sintering procedures.
A series of the modified BNT-BKT piezoceramics encompassing various dielectric and piezoelectric properties was prepared by the addition of three rare-earth ions. These modified BNT composition were calcined in the range of 900℃ for 1-2hr and then sintered at 1100℃ for 2-4hr. Conventional poling was performed at 110℃ with an applied field of 3-4 kV/mm for 20-30 minutes.
The dielectric constant of BNT_(x)-BKT_((1-x))(x=0.86) ceramic is 471 and Curie temperature is 390℃ with the dielectric constant of 7268 and (BNT-BKT)_((1-x))-ST_(x)(x=0.03) ceramic is 837 and Curie temperature is 280℃ with the dielectric constant of 8243. ST addition, the Curie temperature, Tc, decreases rapidly with increasing amount of doped ST.
The mechanical quality factor Q_(m) and electromechanical coupling factor k_(p) of BNT_(x)-BKT_((1-x))(x=0.86) ceramic are very high 205 and 30%. Ni, Mn addition, Q_(m) and k_(p) of (Ni, Mn x=1wat%) 450, 510 and 31%, 32% high.
The k_(p) value (30%) of BNT_(x)-BKT_((1-x))(x=0.86) ceramic is similar to Ni, Mn addition ceramic, but the Q_(m) value is very high compared to BNT_(x)-BKT_((1-x))(x=0.86) ceramics.
