The XRD pattern before and after the annealing treatment of Ba₄Nd₂Fe₂Nb₈O₃₀ sample is shown in Figure 1. In Figure 1, all the diffraction peak position and relative intensities are exactly matching tungsten bronze phase, which means the formation of single-phase tungsten bronze and no other impurity phases. It is different from Josse’s study that he has reported the formation of barium ferrite. Lattice parameters from XRD peak calculated by the least square method is shown in Table 1.

 

Typically, the oxide ceramic with the presence of oxygen vacancies annealing in oxygen, the content of oxygen vacancies will reduce significantly; and annealing in nitrogen, the content of oxygen vacancies will increase significantly. Therefore, when Ba₄Nd₂Fe₂Nb₈O₃₀ ceramics annealing under oxygen and nitrogen, the content of oxygen vacancies will be correspondingly reduce and rise. Reducing of the content of oxygen vacancies will increase the lattice constant and the unit cell volume; and increasing of the content of oxygen vacancies will reduce the lattice constant and the cell volume. So, when Ba₄Nd₂Fe₂Nb₈O₃₀ ceramics annealing under nitrogen and oxygen respectively, the cell volume turns smaller and larger correspondingly.

 

Figure 2 shows the hysteresis loop at room temperature of Ba₄Nd₂Fe₂Nb₈O₃₀ ceramics when no annealing and annealing in oxygen. As the analysis of the dielectric properties, the oxygen vacancies content of the Ba₄Nd₂Fe₂Nb₈O₃₀ ceramic annealing in nitrogen significantly increases, the conductivity decreasing results in the group of samples can not be tested the hysteresis loop. The hysteresis loop of Ba₄Nd₂Fe₂Nb₈O₃₀ ceramic unannealed and annealed in oxygen was observed, indicating that they all have room temperature ferroelectricity. By contrast, the ferroelectric of sample annealing in oxygen is more obvious, residual polarization is large, coercive field is large, and it’s tend to be more saturated.