Phase evolution, Raman spectroscopy and microwave dielectric behavior of (Li1/4Nb3/4) doped ZrO2-TiO2 system

The phase evolution, Raman spectroscopy and microwave dielectric properties of (Li1/4Nb3/4) doped ZrO2-TiO2 system were investigated. The effects of the Zr/Ti ratio and the (Li1/4Nb3/4) substitution were addressed. X-ray diffraction and electron diffraction analysis showed that the crystalline phases of the (Li1/4Nb3/4) doped ZrO2-TiO2 ceramics depended greatly on the Zr/Ti ratio. The sample with Zr/Ti ratio of 7/9 crystallized as Zr5Ti7O24 phase structure, a commensurate structure with a tripled a-axis superstructure and a ZTTZTT sequence. Secondary phase of monoclinic ZrO2 phase appeared when the Zr/Ti ratio was as high as 9/7. Raman analysis showed that the Raman peaks located at 651 and 624 cm−1 were assigned to the vibration modes of Zr-O octahedron and Ti-O octahedron, respectively. The dielectric constant and quality factor (Qf value) of the (Li1/4Nb3/4) doped ZrO2-TiO2 ceramics decreased slightly as the Zr/Ti ratio changed from 6/10 to 9/7. The temperature coefficient of resonate frequency (TCF value) was sensitive to the Zr/Ti ratio and it showed a negative value when the Zr/Ti ratio was close to 5:7. Meanwhile, the TCF value of ZrO2-TiO2 ceramics could also be tailored by the (Li1/4Nb3/4) substitution.