Structural, Raman spectroscopic and microwave dielectric studies on spinel Li2Zn(1−x)NixTi3O8 compounds

Effect of annealing time on structural and microwave dielectric characteristics of Li2ZnTi3O8 ceramics

“…It was noteworthy that the intense and narrow Raman modes are usually observed for well-ordered structure. 24 Lee et al 21 reported that the intensity of Raman active modes was increased with higher sintering temperature, and with longer soaking time, which was suggested that the 1:2 ordered nanoregions grew with sintering temperature and soaking time. Since the symmetric stretching is possible in Li-octahedral, the band 403.40 cm À1 is assigned as A 1g mode of ZnO 4 tetrahedra.…”

“…23 Singh et al 24 indicated that Raman spectroscopy is a useful tool for probing cation occupancy at different sites in cubic spinel Li 2 Zn (1Àx) Ni x Ti 3 O 8 compounds. From the viewpoint of the lattice vibration, a LZT crystal with an ideal cubic spinel structure with space group P4 3 32 symmetry in which the tetrahedral sites are randomly distributed does not show any Raman mode.…”

“…By applying the group theory analysis, it was predicted that LZT has 40 fundamental Raman modes and 22 IR active modes. 24 These compounds, with P4 3 32 space group, possess inversion and according to the mutual exclusive rule, if the compound has center of symmetry, then all Raman active modes are IR inactive and vice versa. Therefore, for these compounds, all Raman modes are IR inactive.…”

“…Therefore, for these compounds, all Raman modes are IR inactive. 24 Figure 6 shows the room temperature Raman spectra of LZT-sintered and annealed samples°C. It can be seen from the Raman spectra of LZT-sintered (t 5 0)°C and annealed (t 5 4 h) samples, only 10 bands were observed whereas in samples that annealed with a holding time of 8 25 Thus, the band that observed at 403.40 cm À1 can be assigned to the Zn-O symmetric stretching vibrations in LZT ceramics.…”

“…It is worth mentioning that the FWHM broadness of the A 1g mode is a measure of dielectric loss in dielectric material. 23,24 Hence, the dielectric loss can be decreased by decreasing in FWHM broadness of A 1g mode. As shown in Table I, the wave number (cm À1 ) of LiO 4 tetrahedra mode for the sintered sample shifted toward a higher wave number (cm À1 ) with higher annealing time (t 5 20 h).…”