MICROWAVE DIELECTRIC-PROPERTIES OF TUNGST EN BRONZE-TYPE BA6-3XR8-SOLUTIONS(2XTI18O54 (R = LA, PR, MD AND SM) SOLID)

A series of tungsten bronze-type solid solutions Ba6-3xR8+2xTi18O54 (R = La, Pr, Nd and Sm) has good microwave dielectric properties. Though the dielectric constant epsilon(r) and the temperature coefficient ta u(i) of resonant frequency change linearly as a function of compositio n x, the quality factor Q.f shows nonlinear behavior of steep increase around x=0.5. The highest gradient was found in the Sm system in whic h the difference in ionic radius from Pa is largest, Increasing of ion ic radii of R, the gradient gradually decreases, Release of inner stre ss which will be caused by the distribution of large ions with differe nt sizes might bring the increase in Q.f When Ba ions remain in the 2 x 2 perovskite blocks which is mainly occupied by R ions in the tungst en bronze structure, the inner stress might become large, Vacancies cr eated by the substitution also bring decrease of the stress. It is als o discussed that the deviation of the composition from the solid solut ions decreases the sintering temperature without influence of the diel ectric properties.