Study On Preparation And Properties Of Yttrium Doped Lithium Niobate Crystal

Lithium niobate has both excellent ferroelectric-piezoelectric properties and non-linear optical properties. So it is widely used in many places. Especially doped lithium niobate crystals obtain an in-depth application. This article conductes a single-doped Y and double-doped Y: Mg in lithium niobate to improve it’s properties.The Czochralski method is used to grow the single crystal. The optimum pulling parameters are get. The pulling rate is 2~4 mm/h. The temperature gradient is 30~50 ℃/cm. The rotational speed is 16~18 r/min. So the doped crystal’s defects have a significant reduction. Then these fine qualified samples are annealed and polished.After the samples tested by X-ray diffraction, the tests find that Y3+ and Mg2+ ions only displace the interior ions in the crystal. When the doping concentrations less than 3 mol%, these doping ions shuold replace NbLi4+ ions at first. High-resolution X-ray diffraction tests confirm that the crystal’s dislocation density is less than 10-7 cm-2and low internal stress. By the high-resolution scanning of the entire wafer z-axis, no mutation of the peak position is found. This confirms that the doping elements are distributed within the crystal uniformly.Differential thermal analysis shows that the Curie temperature of the crystal is proportional to the doping concentration. Y-doped crystal’s infrared absorption peak, UV absorption peak and Raman analysis reflect that Y3+ ions replace NbLi4+ ions in the octahedral at first. The NbLi4+ are completely replaced by yttrium ions when the concentration reaches 3 mol%.With the ferroelectric and the piezoelectric tests, the residual polarization intensity, coercive field value and the piezoelectric coefficient d*33 reduce with the doping concentration’s increasing. So the piezoelectric and ferroelectric properties both decrease. Even they both are down to about 1/2 of the original value.The distortion of the photo-spot test also tells that the crystal’s photo-damage resistant increases several tens times, as an increase of the doping concentration. In particular the 3 mol% single-doped Y and 1 mol% Y: 2.3 mol%Mg double doped crystals, their photo-damage resistant are increased by nearly 520 times and 200 times. The Y, Mg elements create more carriers, resulting in its photoconductive capacity increasing. The photo-damage resistant ability has an inverse relationship with the photoconductive capacity. So the doped crystals’ photo-damage resistant ability is drastically increased.