Birefringence Measurement Of Tiny Grains And Exploring Of Rare Earth Carbonate Crystal Materials

In order to establish a systematic,scientific and effective birefringence test method for tiny grains,we deliberately selected five commonly used optical crystals,Al2O3,SiO2,KDP,LBO,and BBO,with different birefringence sizes as research objects.The five crystals were systematically grinded and sieved into the following four mesh ranges:I 100-170,? 170-270,?270-400 and IV400-600,respectively,and made four samples.Combined with polarization interference method and the principle of complementary color,the birefringence of these samples were measured on a polarizing microscope.The results show that the birefringence is related to the range of mesh size and size of the crystal size.The mean values of the retardation experiment values of the five crystals in the ?270-400 meshe is in agreement with the measured values of the retardation,that is,birefringence experiment values are in agreement with the measured values of birefringence.There are deviations between the retardation experiment values of the 1100-170,?170-270 and IV400-600 mesh ranges and the measured retardation compared to the ? mesh ranges.In the four mesh ranges,when the median size is taken,the measured birefringence value is closest to the theoretical birefringence value.Therefore,the crystals in the range of ?270-400 mesh of the sieve were selected as the test object to test the retardation R,and the median value of the particle size range was taken as the particle diameter d.The birefringence of the crystal can be calculated according to formula R=?nxd.This method will lay a solid foundation for our selection of excellent nonlinear optical crystals.Three new alkaline-rare earth carbonate and carbonate fluorides,KY(CO3)2,Na2Gd(CO3)F3 and NaGd0.25Lu0.75(CO3)F2,were synthesized through the subcritical hydrothermal method.The structures of all the three crystals were determined by the single crystal X-ray diffraction studies.And the measurements of X-ray diffraction patterns and infrared spectroscopy confirmed the accuracy of the structures.The thermodynamic properties of the compounds were determined by thermogravimetric analyses.Theoretical calculations reveal that the three crystals all have large birefringences of 0.105,0.084 and 0.198 which are originated from the microscopic anisotropic polarization and favourable arrangement of[CO3]groups.The synthesis of these three compounds provide a theoretical and experimental guidance for the development and advancement of other deep ultraviolet materials with large birefringence.