Research On New Pyroelectric Crystals

The discovery of pyroelectric effect is a base for laser and infrared detector. Pyroelectric detectors have been widely used in military affairs, planet measure, bank, electric power etc. Although many pyroelectric materials have been discovered, it is not enough for application. TGS crystals are most widely used as pyroelectric materials because of their higher figure of merit. However, the main disadvantages of the crystals, such as lower Curie point and the depolarization, have limited their applications. So, the exploration of new pyroelectric crystal with better merits for application is an urgent work at present.According to the relationship between crystal structure and properties, 13 kinds of glycine series crystals have been grown from aqueous solution. They are glycine zinc chloride, glycine manganese chloride, glycine lithium sulfate and doped TGS crystals. Their structures, growth morphology and pyroelectric coefficient, dielectric constant, dielectric loss, Curie point, spontaneous polarization, figure of merit and hysteresis loop have been comprehensively studied. The information about doping effect has been got from x-ray powder diffraction and IR spectra. The changes of TGS crystalstructures caused by doping have been proved by calculating their lattice parameters.The dopants affect the morphology and physical property of TGS crystal. The dielectric constants of doped TGS descend but the crystal doped with 10% trifluoro acetic acid + 5% glycerin and doped with 10% glyolic acid. For the TGS crystal doped with trifluoro acetic acid and glycerin, the properties are better when the dopant concentrations are equal; the TGS crystal doped with 5mol% glyolic acid, its maximal pyroelectric coefficient increase up to twice that of pure TGS crystal, the dielectric constant just is 1/3 of pure TGS crystal, its quality factor is twice larger than that of pure TGS crystal. It proved that the hydroxyl and carboxyl in the dopant molecule can improve the TGS crystal property. The dopants don't improve the Curie point obviously. A new compound of zinc chloride and glycine has been discovered, and the crystal structure has been analyzed by four-circle diffract meter. The molecular weight of diglycine zinc chloride dihydrate [C4H14Cl2N2O6] is 322.44. The crystal is in the space group C2/c, a=1.4449 nm,b=0.69200 nm,c=1.2970 nm,β=117.890°. Glycine exists as a zwitterion [NH3+CH2COO-], zinc in the structure adopts a distorted tetrahedral coordination geometry, bonded to two chlorines and two carboxyl O atoms of the glycine molecules, the symmetry-center related ZnCl2(C2H5NO2)2 groups are interconnected via hydrogen bonds to form one-dimensional infinite chains extending along the c-axis. The water molecules drop out of coordination.