Research On The Growth Thermodynamics And Kinetic Of L-Alanine Doped ZTS Crystals

Zinc tris (thiourea) sulfate (ZTS), as a new metalorganic nonlinear optical crystal,has the advantage of high laser damage threshold, wide optical transparency and lowangle sensitivity etc, which can be widely used in second harmonic generation (SHG)devices. With the futher studies on growth and performance of the ZTS crystals byscholars, it is expected to become a significant material in the nonlinear optical field.The ZTS crystals also have the shortcoming of small solubility and slow growth rate.Recently, the effect of doping on quality and performance of ZTS crystals has beeninvestigated by scholars at home and abroad. However, the effective method ofimproving the growth rate of crystals hasn’t been found yet. The main researches focuson how to maximize crystal’s growth rate and shorten the growth cycle withoutsacrificing quality of the ZTS crystal.From two aspects of displacement of growth steps and crystals normal growth,growth kinetic of undoped and L-alanine doped ZTS crystals were studied. The mainworks can be summarized as follows:①The solubility of ZTS crystals with different doping concentration of L-alaninein water was measured experimentally. With the increase of temperature, the solubilityincrease under L-alanine doped ZTS solutions.②In situ study of displacement rates of growth steps of different growthconditions on the (100) face of ZTS crystals were observed by using optical microscopy.The effect of different doping concentration of L-alanine, supersaturation and growthtemperature on displacement rates of growth steps was discussed. Experimental resultsshow that with increase of doping concentration, the average displacement velocitiesincrease firstly and then decrease, passing through a maximum under the condition ofthe doping concentration of2mol%L-alanine. Activation energy for single steps andkinetic coefficient for steps were calculated. The kinetic coefficient for steps increasesand activation energy for single steps decreases with L-alanine addition. The scope ofactivation energy for steps of ZTS crystals was calculated under the condition of dopingand without doping according to kinetic coefficient for steps definition.③Under different doping concentration of L-alanine, the crystal growth ratesnormal to the (100),(010) and (001) faces were measured. With increase of dopingconcentration, the growth rate normal to (100) face increases firstly and then decreases and the growth rate normal to (010) and (001) faces decrease firstly, increase secondlyand decrease lastly, passing through a maximum under the condition of the dopingconcentration of2mol%L-alanine; In addition, with increase of supersaturation, thegrowth rate normal to (100),(010) and (001) faces increase linearly. The growth ratenormal to (100) face was found to follow the BCF growth model (R=Aσ) with respectto the supersaturation whereas the growth rates normal to (010) and (001) faces werefound to follow the continuous growth model (R=Aσ) in this paper at the temperature25degrees centigrade and the range of supersaturation between2%and6%. Accordingto crystal growth principles, the normal growth dynamics coefficient of (100),(010) and(001) faces were acquired under the condition of doping and without doping. Underdoping concentration of2mol%L-alanine, the normal growth dynamics coefficient of(100),(010) and (001) faces were maximized, meanwhile, the step edge free energy ofZTS crystal was calculated.