HIGH-TEMPERATURE PHASE-TRANSITION IN KDP-ADP MIXED-CRYSTALS

Mixed crystals of potassium dihydrogen phosphate and ammonium dihydrogen phosphate (KDP-ADP) have been investigated. In the growth mechanism it has been observed that as the concentration of ADP in KDP increases above 20 wt% the quality of the grown crystals deteriorates, probably because the lattice parameters of ADP do not match closely to those of KDP. Dielectric constants (epsilon), loss tangent (tan delta), electrical conductivity (sigma), DTA and ir spectra were measured to see the effect of ADP impurities on KDP. The crystal with 20 wt%. of impurity shows the trend of dielectric and electrical conductivity towards the pure ADP. There is no significant change in the ir spectra measurement between the pure ADP and mixed KDP-ADP at room temperature. X-ray analysis indicates that the lattice constants both a and c begin to increase slightly as the concentration of ADP increases. The DTA measurements show that the first endothermic minimum decreases for both the pure KDP and mixed KDP-ADP samples as the particle size decreases and vanishes when the particle size is less-than-or-equal-to 0.1 mm.