Single crystals of L‐alanine have been grown from buffered aqueous solutions and characterised as to their optical quality via wavefront distortion analysis, electrooptical response and harmonic generation efficiency. Refraction indices as well as phase matching loci were found in satisfactory agreement with previously published data for crystals grown in non buffered solution. Estimates for the electro‐optical response are reported for the first time. The experimentally observed crystal habit is discussed in terms of morphological importance (M.I.), which was found to be in disagreement with the predictions of crystallographic criteria based on the interplanar distance dhkl, on the periodic bond chains (PBC) and the attachment energy Eatt. This disagreement is tentatively attributed to the presence of impurities and non‐appropriate supersaturation conditions.
We have synthesized and characterized a variety of defective AIIB2
IIIX4
VI compounds and alloys, many of which display a layered structure. Here we review and update Raman scattering results on both tetragonal and layered compounds. As to tetragonal compounds we check a simple bond stretching dynamical model, whereas for the layered structures we propose a phenomenological picture of the vibrational dynamics based on the intrinsic high degree of disorder.
We report on the Raman spectra of CdIn,Se, and ZnIn,Se, obtained in a transparency region. These spectra have a disordered-like appearance at high frequencies. A comparison is made with the Raman and IR spectra of the similar compounds CdGa,Se, and ZnGa,Se,. The overall vibrational behaviour is mainly determined by the anion and a correspondence may be observed between the frequencies of some high energy polar modes. A strong non-polar breathing mode is observed at nearly the same frequency in all these compounds. The observed similarities between the spectra are discussed within the frame of the existing simplified models.
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