ROLE OF BI2O3 IN OPTIMIZING THE DIELECTRIC-PROPERTIES OF BA4.5ND9TI18O54 BASED MICROWAVE CERAMICS

Small additions of Bi2O3 Or bismuth titanate improve the dielectric pr operties of Ba4.5Nd9Ti18O54 at microwave frequencies. It was found tha t Bi3+ can replace Nd3+ up to 15 mol%, the limiting composition of sol id solution being Ba-4.5(Nd0.85Bi0.15)(9)Ti18O54. At the solid solutio n limit the temperature coefficient of resonant frequency attains its minimum value. The modified ceramic is distinguished by high permittiv ity of 99 and a e-value of 5500. The temperature coefficient of resona nt frequency is low, 15 ppm/K. After exceeding the solid solubility li mit, additional Bi2O3 concentrates as a Bi-rich phase at the grain bou ndaries, causing considerable reduction of the e-value and an increase of tau(f).