Structure and Microwave Dielectric Properties of Low Temperature Sinterable NaR5(MoO4)8 (R=La, Pr, Nd, Sm) Ceramics

Phase pure NaR5(MoO4)(8) (R=La, Pr, Nd, Sm) ceramics were prepared by a conventional solid-state ceramic route at low sintering temperatures. Powder x-ray diffraction studies were performed to confirm the phase purity of the samples. The presence of MoO42- tetrahedra in the crystal structure was confirmed by Raman spectroscopy of the samples. Surface morphology investigations using scanning electron microscopy show that the sintered samples have compact microstructure and phase homogeneity. The microwave dielectric characterization of the sintered ceramics show that the samples have excellent quality factor, low temperature coefficient of resonant frequency and hence are ideal candidate materials for microwave circuit applications. The NaR5(MoO4)(8) (R=La, Pr, Nd, Sm) ceramics possess epsilon(r) from 10.6 to 11.5, quality factor Q(u)xf from 56200GHz to 78600GHz, temperature coefficient of resonant frequency (f) from -42ppm/C-o to -72ppm/C-o and linear thermal expansion coefficient CTE ranging from +8.75ppm/degrees C to +11.54ppm/degrees C. The chemical compatibility of the ceramics with silver electrodes was determined by x-ray diffraction and energy dispersive x-ray spectroscopic analyses of the silver co-fired ceramic samples.