New dielectric material systems of Sr sub(x)Nd sub(2(1)- sub(x)/3)TiO sub(3) perovskites-like at microwave frequencies

Perovskite compounds, Sr sub(x)Nd sub(2(1-x)/3)TiO sub(3) (SNTx) with x ranging from 0.05 to 0.2, were prepared by the conventional solid-state reaction method. X-ray diffraction patterns illustrated that high density and single phase products were obtained for all samples, indicating that a small level of Sr addition could substantially stabilise the structure and maintain a single phase for Nd sub(2/3)TiO sub(3) ceramics. But there was also an orthorhombic space groups transition from Pnma to P4/mmm when x was above 0.18. In addition, the dielectric constant ( epsilon sub(r)) of SNTx ceramics had improved from similar to 85.6 to similar to 112 with increasing x value due to the larger ionic polarizability of Sr super(2+) than that of Nd super(3+). Notably, the product of dielectric Q value and resonant frequency (Q f) of similar to 295-650 at 3.07-3.32 GHz was strongly dependent on the grain size and the cation deficient in the present systems. Either increasing grain size or decreasing A-site vacancies led to an increase in the Q f value. Besides, a temperature coefficient of resonant frequency ( tau sub(f)) of the SNTx ceramics sintered at their optimum densification temperature gradually increases from 191.7 ppm/ degree C (x = 0.05) to 221.3 ppm/ degree C (x = 0.2), which results from the lower rattling effect and higher symmetry in BO sub(6) octahedra of perovskite structure according to bond valence theory and tolerance factor (t).