CRYSTAL-GROWTH AND PHYSICAL-PROPERTIES OF MONOCLINIC L-ARGININE HYDROCHLORIDE MONOHYDRATE, C6H14O2N4HCL.H2O, AND L-ARGININE HYDROBROMIDE MONOHYDRATE, C6H14O2N4HBR.H2O

Single crystals of optical quality of L‐arginine HCl · H2O and L‐arginine HBr · H2O with dimensions up to 80 × 60 × 30 mm have been grown from aqueous solutions by controlled evaporation at about 310 K. The isotypic crystals exhibit a quite similar behaviour with respect to morphological, pyroelectric, dielectric, optical, thermal expansion, electrostrictive, electrooptic, elastic, thermoelastic and non‐linear optical properties. A distinct anisotropy of the longitudinal elastic stiffness is observed with a maximum along the direction of the alignment of the arginine ions. Nearly in the same direction a minimum of thermal expansion, dielectric constant and index of refraction is found. The pyroelectric, electrostrictive, electrooptic and non‐linear‐optical effects are of only mediocre magnitude except the electrostrictive constant d211 which surmounts the longitudinal electrostrictive constant d111 of alpha‐quartz by a factor three. Copyright © 1990 WILEY‐VCH Verlag GmbH & Co. KGaA