Study on Al2O3 and ZrO2 doped LiNbO3 ceramics and the sputtered thin films

In this study, aluminum oxide (Al2O3) and zirconium oxide (ZrO2) were selected as dopants to investigate their effects on the microstructure and properties of lithium niobate (LiNbO3) polycrystalline ceramics and amorphous thin films. LiNbO3 ceramics were prepared using cold isostatic pressing (CIP) and sintering methods. The thin films were deposited via radio frequency (RF) magnetron sputtering method. The results indicate that, under a sintering regime of 1000 degrees C for 3 hours, the relative density of ZrO2 doped LiNbO3 ceramics reached 96.6 %. Both Al2O3 and ZrO2 doping improved the sintering quality of LiNbO3 ceramics. 10 mol% Al2O3 doping fully integrated into the LiNbO3 lattice, causing lattice contraction due to the smaller ionic radius of Al ions and the elimination of intrinsic lithium vacancies. Conversely, 10 mol% ZrO2 doping did not fully integrate into the LiNbO3 lattice, resulting in the presence of a ZrO2 phase in the XRD patterns and slight lattice expansion due to the partial incorporation of Zr ions. The doping of Al2O3 and ZrO2 introduces a secondary phase in polycrystalline LiNbO3 ceramics, reducing the bulk resistance of the ceramics from 500 M Omega to 128 M Omega and 102 M Omega, respectively. The ionic conductivity of ZrO2 doped LiNbO3 thin films was measured at 2.7 x 10-5 S/cm, with no significant changes in optical transmittance and microstructure, making them suitable for use as transparent solid electrolytes in various devices.