Raman spectra analysis for Ba[(Mg1- x Ni x )1/3Nb2/3]O3 microwave dielectric ceramics

Abstract

Raman spectra analysis has been carried out for both the as-sintered and annealed Ba[(Mg1−xNix)1/3Nb2/3]O3 ceramics. Based on the harmonic resonant model, all the Raman modes are successfully assigned according to the effects of ion substitution and post-densification annealing. All of the as-sintered samples present 7 normal modes as predicted by factor group analysis; an extra mode at around 560 cm−1 exists in x = 0.6-1.0. The 3 modes Eg(O), Eg(Nb), A1g(Nb) between 150-350 cm−1 decrease in intensity with increasing x, agreeing well with the variation of ordering degree. By post-densification annealing for x = 0.4, a strong dependence on ordering degree has been proved for the A1g(O) mode at around 790 cm−1. For the as-sintered samples, the Q × f value correlates well with the oxygen octahedron stretch mode A1g(O), while the dielectric constant εr is dominated by ionic polarizability rather than the rigidity of the oxygen octahedra. After annealing, the Raman modes are intensified, corresponding to the enhancement of cations ordering. The annealing significantly increases the A1g(O) Raman shift and decreases the FWHM (full width at half maximum) of A1g(O) mode, resulting in the increase of εr and the improvement of Q × f value for each composition. The intensity ratio of A1g(Ba)+Eg(Ba) mode to A1g(O) mode increases after annealing, implying that A1g(Ba)+Eg(Ba) is more dominant in the ordered structure.

Crystal structures and microwave dielectric properties of (1-x)Ba(Zn1/3Nb2/3)O3 − xBaWO4 (0 ≤ x ≤ 0.25) ceramics

“…With the increase of W 6+ concentration, the shift of B-site ions ordering degree in the oxygen octahedron led to the change of the coherency, which in turn resulted in the variation in the FWHM of the Raman peaks [26]. The dielectric properties of composite perovskite ceramics were closely correlated with the A 1g (O) peak reported in many studies [27,28]. From figure 6, as BaWO 4 concentration increased, the FWHM of the A 1g (O) peak was inversely correlated with the Q × f value.…”

Octahedral distortion due to oxygen vacancy reduction in La3+ modified BNT-BTO solid solutions near morphotropic phase boundary

“…This is due to the presence of different cations in the same sites, which affects the overall Raman modes. Different Raman modes along with the FWHM of all the samples are listed in table 5, which is inconsistent with the other reported values [49]. It is observed that the peak positions of the different Raman modes vary compared to the pure BNBTO solid solution, which confirms the variation of local symmetries of the structure due to the La substitution.…”

“…It may be due to the reduction in octahedral distortion and leads to the decrease of the bond length between different ions. The decrease in bond length enhances the stiffness of the bond, which requires higher energy (wavenumber) to vibrate and leads to an increase in the Raman shift [49]. Finally, the D modes near 820 and 998 cm −1 show no regular variation on substitution.…”

Influences of Mg and Mn doping on structure, B-site ordering and microwave dielectric properties of Ba(Co1/3Nb2/3)O3 ceramics

“…We would like to mention that the splitting of the reflections (422) and (226) usually is a strong evidence to trace the appearance of B-site 1:2 ordering in Ba(B' 1/3 B'2 /3 )O 3 ceramics with complex perovskite structure [28]. It is interesting that the splitting of the reflections (422) and (226) at 2θ≈114°-116°, which results in the broadening of the peak, is observed clearly in as-annealed [29][30][31], four obvious peaks in as-sintered BCN ceramics are observed. They include F 2g (Ba) mode centered at ∼105 cm −1 related to Ba lattice site-related vibrations, F 2g (O) modes centered at ∼375 cm −1 and 450 cm −1 related to oxygen layers, and A 1g (O) mode centered ∼800 cm −1 correlated with stretch vibration of oxygen octahedra.…”