C. Razzetti

Solution Growth and Characterisation of L-alanine Single Crystals

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 d hkl , on the periodic bond chains (PBC) and the attachment energy E att . This disagreement is tentatively attributed to the presence of impurities and non-appropriate supersaturation conditions.

Ternary and pseudoternary AB2X4 compounds (A = Zn, Cd ; B = Ga, In ; X = S, Se)

Abstract Multication compounds are considered to have interesting applications. Among the variety of possible AmBnXp materials, however, the research work has been unevenly distributed, as the ABX2 chalcopyrites have attracted the majority of the efforts. The related family of AB2X4 defect chalcopyrites, which is characterized by an ordered sublattice of vacancies and then by a further degree of freedom as to tailoring possibilities, has on the other hand received much less attention. Here we discuss the results obtained in the crystal growth and in the structural and dynamical (Raman) analysis of about sixty different ternary and pseudoternary AB2X4 compounds or phases. The reaction products can be grouped in three different structural families: cubic-spinel AB2X4 structures (CdIn2S4 like), AB2OX4 layered hexagonal structures (ZnIn2S4 like) and AB2□X4 defective tetragonal structures (CdGa2S4 like). Our attention has been primarily devoted to the defective phases, which have been obtained in the great majority of the starting compositions studied.

A comparison of the raman spectra of ZnGa2Se4 and other gallium defect chalcopyrites

Abstract We report and comment for the first time the Raman spectrum of ZnGa2Se4. Looking for family trends we compare the present results with those obtained in other gallium defect chalcopyrites. The proportionality law between the frequencies of corresponding phonons in different compounds is verified for all the modes with the exception of the lowest energy polar modes. Evidence of the peculiarity of these modes is obtained, confirming what reported for ZnxCd1-xGa2S4 pseudoternary compounds.

Raman scattering of the ordered-vacancy compound CdGa2Se4

The first-order Raman spectrum of the ordered-vacancy semiconducting compound CdGa2Se4 is described for the first time. The symmetries of the k=0 vibrational modes are assigned through a polarisation angular analysis of the spectra. The longitudinal and transverse frequencies of the polar B type modes have been determined. The results fit the hypothesis of a single formula unit, i.e. seven atoms per unit cell.

Structure and lattice dynamics of nonmagnetic defective AIIBIII2XIV4 compounds and alloys

Abstract We review the results in the synthesis and in the structural (X-ray, EXAFS) and dynamical (Raman) characterization of AB2X4 compounds and of several alloys obtained by isoelectronic partial substitution of the ions.

On the lattice dynamics of some defective gallium ternary compounds

The authors point out that a proportionality law connects the frequencies of corresponding vibrational modes in the gallium defect chalcopyrites CdGa2Se4, CdGa2S4 and ZnGa2S4. They present a simple dynamical model based on the approximation of independent cation-(anion)4 tetrahedra. The agreement of this model with experiment is satisfactory.

EXAFS study of mixed crystals of the AIIBIII2XVI4 family

Abstract In this work we studied the nature of the near-neighbour environment in ternary and pseudoternary defect chalcopyrites of the AB 2 X 4 family by using the extended X-ray absorption fine structure (EXAFS) technique. The EXAFS was measured at the K-edge of Zn, Ga and Se elements in ZnGa 2 (S x Se 1-x ) 4 and Ga and Se edges in CdGa 2 (S x Se 1-x ) 4 mixed crystals.NN distance were determined for all the compositions by a linear fitting of differences of phases and by a fitting procedure in k-space. We found bond lenghts nearly constant and close to the respective distances in the end member crystals over all the composition range, whereas the unit cell parameter a(x) changes accordingly to the virtual crystal approximation (Vegards law).

Raman scattering in defect chalcopyrite crystals

SummaryRaman-scattering measurements on the defect chalcopyrite compounds CdGa2Se4, CdGa2S4, ZnGa2S4 are reported. The phonon picture is consistent with the

Preparation and Raman spectroscopy of Zn x Cd1−x In2S4 mixed cation layered compounds

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