Study On Preparation And Electrical Properties Of Candium Doped Lithium Niobate Crystal

Rotation-pulling method was used to prepare pure lithium niobate andscandium doped lithium niobate single crystals successfully. The grown crystals areof fine quality and free of macroscopic defects. The most appropriate technologicalparameters for growing doped crystals was determined. For pure and lightly dopedcrystals, the pulling velocity, rotation speed and axial temperature gradient arerespectively4mm/h,18r/min and40-50℃. While for heavily doped crystals, theseparameters are respectively2mm/h,16r/min and30-40℃. In theory, the factorswhich have impacts on the quality of the crystal such as the pulling velocity,temperature gradient and rotation speed were systematically analyzed. The crackingand twin crystal problems were solved successfully. And the production efficiencywas improved.X-ray powder diffraction (XRD) was used to analyze the crystal structure andthe basic properties of the scandium doped lithium niobate single crystal. Theresults show that doping does not change the original crystal structure and there isno new phase formed. This implies that scandium have either replaced the niobiumor the lithium atoms, rather than occupying the interstitial positions in the crystal.The sizes difference between scandium particle and original particles in lithiumniobate crystal could bring lattice deformation and lattice parameter change. This isalso proved in test.Rocking curves from high resolution X-ray diffraction are sharp, symmetryand with small half-peak width. This can prove that the grown crystals are complete.Each of the rocking curves has only one peak which illustrates that the internalstress in the crystal is small and the defects are rare. Dislocation density in thecrystals is found to be under10-7cm-2through calculation, which is very low.Differential thermal analysis was used to evaluate the influence of thescandium concentration on Curie temperature. The result shows that crystals’ Curietemperature increases with the increasing of scandium concentration. The Curietemperature of2.0mol%doped crystal is33℃higher than the pure crystal. It isassumed that this may be caused by the changing of the spontaneous polarization.Besides, the ferroelectric synthetical analysis system was applied to researchthe electrical properties of the crystal materials. The ferroelectric test result showsthat with the increasing concentration of scandium, the intensity of spontaneouspolarization, polarization intensity and the coercive field reduce. This shows that crystal defect is a key factor which affect the ferroelectricity of the crystal. Whenthe doping concentration increases, the doping ions will replace the normal lithiumions. The electronegativity of scandium ion is larger which will lead to the changeof polarization, so the addition of scandium ion can bring the change of theelectrical properties. Piezoelectric test results show that with the increasing ofscandium doping concentration, the piezoelectric coefficient d*33decreases from85.8to22, a75%drop. However, the pyroelectric coefficient rises to33.4325×10-4cm-2k1-from17.4325×10-4cm-2k-1when the doping concentration reach to2.0mol%from0.0mol%. Dielectric analyzer was applied to analyze crystals’ dielectricproperties. The results show that with the increasing of the concentration ofscandium, the dielectric constant have increased about three times and the dielectricloss shows a70%decline.