Dielectric constant is related to electric polarization while quality factor is related to dielectric loss which depends on lag of polarization with a.c. field. Hence, two quantities are quite different. If one decreases, other may increase. It is not surprising in your case.
Thanks for your kind information and i know, but i want to know it in term of soft mode Phonon. Because Dielectric constant is inversely related to the soft mode phonon? The dielectric constant and TCF decrease monotonically while quality factor increase, with cerium addition.