The dielectric properties of Ba(Mg1/3Ta2/3) O3 and Ba(Mg1/3Nb2/3)O3 ceramics were investigated using Fourier transformed infrared and Raman spectroscopies. The real part of dielectric constant of these materials decreases when the heavier Ta atoms replaced the lighter Nb atoms, which is closely related to the shift of mode-frequency. The Q -factor of the materials depends weakly on the composition. The decrease in Q -factor with the frequency is due to the presence of a resonance mode at around 3 THz. Larger width of the breathing Raman mode, A1g[O], correlates very well with the lower Q-value of the BMN materials, as compared with the BMT materials.
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