Research On The Microscopic Growth Kinetics And The Quality Of ZTS Crystals With Different PH Values

Zinc tris（thiourea） sulphate （{Zn[CS（NH₂）₂]₃SO₄}, ZTS） is a typical representativeof metal-organic coordination compound of the nonlinear optical crystal, which has highnonlinear optical coefficient, wide range of light transmission, high laser damagethreshold and low angular sensitivity, etc. In addition, the physical and chemicalproperties of ZTS crystal is relatively stable, and ZTS crystal has high mechanicalstrength, synthesis easily and so on, thus, the growth and preparation process of ZTScrystal have been paid more attention.Currently, the influence of additives mainly on the optical properties, crystalquality and macroscopic growth rate of crytal has been investigated by domestic andforeign scholars, however,the micro growth kinetics of ZTS crystal was few studied,espically the mean displacement velocity of steps on the （100） face of ZTS crystal underdifferent pH value solution and different supply speed of solution, as well as the studyof step kinetics have not been found so far, however, the growth of macroscopic crystalscan be guided by microscopic growth kinetics studies. In view of the above, the stepgrowth kinetics and growth quality of ZTS crystal are researched under differentconditions, the main contents and conclusions are as follows:①The solubility of ZTS crystal with different pH value solution was measured,and the solubility curves are obtained. The solubility of ZTS crystal increases graduallyalong with the rise of temperature, but the solubility-temperature coefficient wasrelatively low. At the same temperature （especially high temperature）, the pH valuealmost has no effect on the solubility of ZTS crystal.②Compare to the pour solution （pH=4.9）,the metastable zone width test of ZTSsolution with different pH value （4.2,4.9,5.5） show that the metastable zone width ofZTS solution will be widened whether the pH value of ZTS solution is raised or lowered,meanwhile, with the same pH value, the metastable zone width of the solution willincrease with the rise of temperature.③The mean displacement velocity of steps on （100） face of ZTS crystal underdifferent condition were studied by using optical microscopy. From the plot of the meandisplacement velocity of steps V against pH value, it is found that V reaches themaximum when pH=4.2; From the relationship between the mean displacement velocityof steps V against supersaturation σ in pure ZTS solution （pH=4.9）, the dead zone and critical supersaturation of ZTS crystal were determined, which is σd=2%and σ*=4%respectively, the step kinetics coefficient β1and the activation energy of growth unit E atdifferent supersaturation stages are calculated.④According to the curve of the mean displacement velocity of steps V againstsupersaturation σ with different pH values, step kinetic coefficient β1and the activationenergy of growth unit E are calculated. Meanwhile, the supply speed of solution has adirect impact on the mean displacement velocity of steps, when s≈1.2ml/min, V reachesthe maximum.⑤The observation of dislocations and the result of infrared spectroscopyexperiments on ZTS crystals which grown from different pH value solutions indicatedthat when pH=4.2, the density of dislocation pits is the smallest and the opticaltransparency is the largest, that is to say, the quality of the crystals has been improved.