Structure and Microwave Dielectric Properties in the x Ca2AlNbO6: (1-x) Ca3Nb2O8 System

Julia Y. Chan, T. A. Vanderah, R.S. Roth, W. Wong-Ng, B.A. Reisner,§ R.G. Geyer*

National Institute of Standards and Technology, Ceramics Division,
§NIST Center for Neutron Research
Gaithersburg, MD 20899
*Radio-Frequency Technology Division, Boulder, CO 80303

The structure and dielectric properties of bulk ceramics in the xCa2AlNbO6: (1-x)Ca3Nb2O8 system were studied. Ca2AlNbO6 (P21/na = 5.3785(1) Å, b = 5.4158(1) Å, c = 7.6259(1) Å, b = 89.93(1)o) is a double perovskite with structure similar to CaTiO3 and Ca3Nb2O8 is a defect perovskite-related phase (a = 23.803(1) Å).  The end members exhibit temperature coefficients of resonant frequency (Df) that are opposite in sign; therefore, compositions along the tie line between them were prepared to examine the dielectric properties.  Materials in this system exhibit modest relative permittivities (24 < er < 39) and low dielectric loss (7000 < Q x f < 14000 at 6 GHz). At the composition near x = 0.6, the relative permittivity is 26 with Df near 0 ppm at 7 GHz. Synthesis, structural characterization from single-crystal X-ray and powder neutron diffraction, and the dielectric properties of the phases will be described.