Compositional dependence of morphology and lattice parameters during growth of K1-x(NH4)xH2PO4 mixed crystals

✍ Scribed by K. Srinivasan; A. Cantoni; G. Bocelli

• Publisher: John Wiley and Sons
• Year: 2010
• Tongue: English
• Weight: 257 KB
• Volume: 45
• Category: Article
• ISSN: 0232-1300
• DOI: 10.1002/crat.200900656

✦ Synopsis

Mixed crystals of ammonium dihydrogen phosphate and potassium dihydrogen phosphate K 1-x (NH 4 ) x H 2 PO 4 were grown from aqueous solutions with x = 0.06, 0.09, 0.15, 0.32, 0.42, 0.51, 0.63, 0.70, 0.76, 0.78, 0.84, 0.88, 0.89 and 0.91. The crystal composition that differs from solution was estimated by X-ray method. Morphology of the crystals changes from tetragonal prism to needles when the incorporation of either of the two components into the other; which also affects the growth rate along the prominent growth directions significantly. Growth along the [001] decreases initially with composition and reached the maximum when x = 0.5; whereas growth along the [100] always showed a decreasing trend with composition and attained a minimum value when x = 0.5. Crystal length along the [001] and [100] and aspect ratio are also compositional dependent. Unit cell parameters determined by X-ray powder and single crystal analyses revealed that the 'a' parameter shows only a small and linear variation but the 'c' parameter changes significantly with ADP incorporation because of the difference in the effective ionic radius of K + and NH 4 + ions and also the possibility of NH 4 + ion to form two different kinds of hydrogen bonds in the system. The existence of a pseudo-cubic cell at the mixing composition x = 0.78 was also revealed.