Molten salt synthesis of Gd-doped SrBi${}_2$Ta${}_2$O${}_9$ ceramics with enhanced dielectric properties at room temperature

A binary NaNO${}_3$-KNO${}_3$ (45-54% weight ratio) solar salt was used to prepare Gd-doped SrBi${}_2$Ta${}_2$O${}_9$ compounds. It is found, through the X-ray diffraction technique, that the solubility of Gd${}^{3+}$ ions in the Bi${}^{3+}$ site leads to cell volume shrinkage. Among the experienced difficulties figuring out mainly the undesired reaction that could occur between raw materials and molten-salt mixture involving a secondary phase. Fourier transform infrared and Raman techniques revealed that the incorporation of gadolinium into SrBi${}_2$Ta${}_2$O${}_9$ lattice brings small shifts in vibrational frequency. The string process used in this work has led to non-negligible mass loss, which effectively affects the experimental density of ceramics. Along with scanning electron microscopy, the ceramics not only are composed of plat-like grains but also, they are reduced in thickness by doping. Compared with the pure SrBi${}_2$Ta${}_2$O${}_9$, dielectric constant and dielectric loss of doped samples with different gadolinium concentrations are significantly enhanced. However, both constants, since carrier generation is the same under a different bias voltage. Meanwhile, the long-distance motion of the charge carriers' conduction mechanism depends, mainly, on microstructure and gadolinium concentration rather than bias voltage. The undoped sample is almost n-type conductivity that is predominant in oxygen-deficient. The more gadolinium is introduced into the structure the more the radius of Nyquist impedance is expanded, leading to the reduction of oxygen vacancies.