Study On The Optimal Growth And New Functional Properties Of ZCTC Crystal

Zinc cadmium thiocyanate[ZnCd(SCN)4,abbreviated as ZCTC]crystal is an important bimetallic thiocyanate complex compound.Among the four crystals of manganese mercury thiocyanate,cadmium mercury,zinc mercury thiocyanate[MnHg(SCN)4,CdHg(SCN)4,ZnHg(SCN)4,abbreviated as MMTC,CMTC,ZMTC]and ZCTC,ZCTC crystal possesses the shortest transparency cutoff and the widest transparency region.It has widespread application in the field of miniature blue violet laser.In addition,the structure of ZCTC crystal is highly distorted and non-centrosymmetric,and the stretching vibration of-C = N-can produce large Raman shift(more than 2000 cm-1),which will be beneficial to direct acquisition of high efficient near mid infrared Raman laser directly through first order Stokes displacement.And then,ZCTC crystal has more excellent functional applications,such as piezoelectric and stimulated Raman scattering(SRS).The purpose of the dissertation is to optimize the growth method and explore the new function of ZCTC crystal.The stability of the ZCTC crystal growth solution,the elastic and thermal properties of ZCTC crystal were deeply explored.Meanwhile,combined with the first principle,Material Studio software was used to optimize the structure of the four crystals,and the elastic constants were calculated.1.Crystal growthThe raw material of ZCTC was synthesized by using high purity raw materials.After dissolution,the growth of ZCTC crystal was carried out by slow solvent-evaporation method and temperature-lowering method.the micro-crystallization method was used to investigate the growth habit in aqueous solutions,and then,the best pH value for crystal growth was obtained.In the meanwhile,the solubility curve of the growth solution of ZCTC crystal with the best pH value was measured,and the stability of the solution was studied.Experimental results showed that the best pH value for crystal growth of ZCTC crystal from aqueous solutions was ranging from 3 and 5.The growth temperature region of the crystal grown by temperature-lowering method was 30-50 ?.The crystal with dimensions up to 51×15×12mm3 have been obtained by slow solvent-evaporation method.Two-dimensional nucleation growth mechanism and crystal twinning defects were observed from the as-grown crystals.The existence of crystal twinning defects was mainly due to the fact that Cd(?)ions could be coordinated with N atoms or S atoms in ZCTC solution.Therefore,there were three distorted polyhedron structures of ZnN4,CdS4 and CdN2S4 in the structure of ZCTC crystal.2.Elastic and thermal properties of ZCTC crystalAccording to the axis selection principle of the coordinate axes of the tetragonal crystallographic system,crystal cutting for elastic constants measurement were determined.The relative dielectric constants at different frequencies and elastic compliance constants at room temperature were measured.ZCTC crystals had modest relative dielectric constant(?31=8.97 and ?33=9.31),larger elastic compliance constants(?33=11.58 pm2/N,?44=151.06 pm2/N and s12=119.70pm2/N).The thermal diffusivity of ZCTC.crystal was measured by laser flash method.According to the thermal expansion coefficient of ZCTC crystal,the density of crystal at different temperatures was calculated,and then the thermal conductivity of ZCTC crystal was calculated according to the formula The density of ZCTC crystal decreased linearly with the rise of temperature.The thermal conductivities along the a and c-axes decreased from 1.3683 to 0.8739 W m-1·K-1 and 0.8496 to 0.5356 W m-1·K-1 as the temperature increased from 303 to 423 K,respectively.3.Theoretical calculationThe structures of ZCTC,MMTC,CMTC and ZMTC were optimized by the CASTEP module of Material Studio software,and the elastic constants of the four crystals were calculated.The differences between the calculated values and measured data of ZCTC crystal were compared,and the reasons were analyzed.This would lay the foundation for the day after looking for a much better calculation method.