Weijia Luo

Oxygen vacancy regulation and its high frequency response mechanism in microwave ceramics

Li2ZnTi3−xMxO8 {M = Al3+, Nb5+, (Al0.5Nb0.5)4+, (Zn1/3Nb2/3)4+, and (Li1/4Nb3/4)4+} systems were fabricated by a facile solid-state reaction method. According to the substitution rule of radius and valence, all of the doping ions {Al3+, Nb5+, (Al0.5Nb0.5)4+, (Zn1/3Nb2/3)4+, and (Li1/4Nb3/4)4+} should occupy Ti4+ sites. EPR spectra showed that paramagnetic Ti3+ centers and oxygen vacancies co-existed in the pure Li2ZnTi3O8 ceramics. The oxygen vacancies in Li2ZnTi3O8 were attributed to the deoxidation process during high temperature sintering. The inhibitory effects of acceptor ion, donor ion and co-doped ions on oxygen vacancies were related to the lattice energy (U) of O(1). An appropriate amount of (Al0.5Nb0.5)4+, (Zn1/3Nb2/3)4+ and (Li1/4Nb3/4)4+ greatly reduced the microwave dielectric loss of the Li2ZnTi3O8 systems. And, the microwave dielectric loss deteriorated seriously in Al3+-doped systems. For the first time, a systematic exposition on the response process of dielectric loss in Li2ZnTi3O8 ceramics was discussed based on the ac impedance analysis and terahertz time-domain spectroscopy (THz-TDS) analysis in detail. Deeper analysis revealed that the absorption of structural phonon oscillation and long-range movement of weakly bound defects () were two major contributors to the microwave dielectric loss.