Abstract
Cubic pyrochlore (Bi1.5Zn0.5)(Zn0.5−x∕3TixNb1.5−2x∕3)O7 ceramics with 0⩽x⩽1.5 were synthesized and investigated between 100Hz and 100THz by means of broadband dielectric spectroscopy, time-domain terahertz transmission spectroscopy, Fourier transform infrared reflectivity spectroscopy and Raman scattering. Bi1.5ZnNb1.5O7 exhibits a microwave dielectric relaxation which slows down and broadens remarkably on cooling. Careful structural investigations confirmed that the relaxation originates in hopping of disordered Bi and part of Zn atoms in the A sites of the pyrochlore structure. Substitution of Ti atoms to the B sites, i.e., increasing x, results in an increase of the microwave permittivity from 150 to 200 of the relaxation frequency and also of the microwave quality Q. Low temperature Raman scattering experiments did not reveal any phase transition in the samples under study.
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