Preparation, Structure And Dielectric Properties Of Sr₅LnTi₃Ta₇O₃₀ Ceramics

The aim of this thesis is to explore and develop new high dielectric microwave materials as well as free lead compensated dielectric ceramics with tungsten bronze (TB) structure. According to the characteristic of tungsten bronze structure, series of new tantalates Sr5LnTi3Ta7O30 (Ln= La , Nd, Sm, Y) were designed on the basis of Ba5LnTi3Ta7O30 through the substitution of A cation with elements Nd, La ,Sm and Y, respectively. Furthermore, their structure and dielectric properties were studied.Firstly, Sr5LnTi3Ta7O30 (Ln=Nd, La, Sm, Y) compounds were synthesized by high temperature solid state reaction technique and characterized by scanning electron microscope (SEM), x-ray powder diffraction (XRD) and chemical analysis. The results show that the structure of Sr5LnTi3Ta7O30 (Ln=Nd, La, Sm, Y ) belongs to tetragonal tungsten bronze structure.Secondly, the dielectric properties of Sr5LnTi3Ta7O30 (Ln=Nd, La, Sm, Y;) were studied. Through the dependence of dielectric constant vs temperature, Curie temperature (Tc) region and structural phase transitions were determined. The experiment results indicated that the dielectric properties of Sr5LnTi3Ta7O30 (Ln=Nd, La, Sm, Y; ) varied with different Ln , but all of them have high dielectric constants. The temperature coefficients of the dielectric constant(εr) is much smaller compared with that of TB compounds in the Ba5LnTi3Ta7O30 system .Finally, the dielectric constants of Sr5LnTi3Ta7O30 (Ln=Nd, La, Sm, Y; ) were calculated by using Clausius-Mosotti equation with polarizabilities of ions. The calculated values are much smaller than the experimental values. The deviations are worthy to further study.