High frequency dielectric properties of A5B4O15 microwave ceramics

High-frequency dielectric properties of A5B4O15 ~A5Ba, Sr, Mg, Zn, Ca; B5Nb, Ta! dielectric ceramics are studied by means of the microwave cavity technique, a combination of far-infrared reflection and transmission spectroscopy and time-resolved terahertz transmission spectroscopy. Microwave permittivity e8 and Q3 f factor vary, depending on the chemical composition, between 11 and 51, and 2.4 and 88 THz, respectively. The temperature coefficient t f varies between 273 and 232 ppm/°C, and in two samples ut f u is less than 15 ppm/°C. It is shown that the microwave permittivity e8 of the ceramics studied is determined by the polar phonon contributions and that linear extrapolation of the submillimeter dielectric loss e9 down to the microwave region is in agreement with the microwave data of single phase samples. The relationship among phonon spectra, the crystal structure, and the unit cell volume is discussed. © 2001 American Institute of Physics. @DOI: 10.1063/1.1351873#