High frequency dielectric properties of A(5)B(4)O(15) microwave ceramics

High-frequency dielectric properties of A(5)B(4)O(15) (A=Ba, Sr, Mg, Zn, Ca ; B=Nb, Ta) dielectric ceramics are studied by means of the microwave cavit y technique, a combination of far-infrared reflection and transmission spec troscopy and time-resolved terahertz transmission spectroscopy. Microwave p ermittivity epsilon' and Qxf factor vary, depending on the chemical composi tion, between 11 and 51, and 2.4 and 88 THz, respectively. The temperature coefficient tau (f) varies between -73 and 232 ppm/degreesC, and in two sam ples parallel to tau (f)parallel to is less than 15 ppm/degreesC. It is sho wn that the microwave permittivity epsilon' of the ceramics studied is dete rmined by the polar phonon contributions and that linear extrapolation of t he submillimeter dielectric loss epsilon' down to the microwave region is i n agreement with the microwave data of single phase samples. The relationsh ip among phonon spectra, the crystal structure, and the unit cell volume is discussed. (C) 2001 American Institute of Physics.