Denis Balitsky

The 3543 cm -1 Infrared Absorption Band in Natural and Synthetic Amethyst and Its Value In Identification

tionship between conditions of formation and the absorption spectra of natural and synthetic amethyst in the 3800–3000 cm-1 region to determine whether infrared spectroscopy can be used to identify synthetic origin (see Balitsky et al., 2003, 2004). Previously it was shown that both natural amethyst and synthetic amethyst grown in alkaline solutions share similar spectral features in this region (Balakirev et al., 1979; Zecchini, 1979; Balitsky, 1980; Lind and Schmetzer, 1980; Zecchini and Smaali, 1999). Two absorption bands are almost always present in both types—an intense feature at 3585 cm-1 and a relatively weak one at 3612 cm-1— due to the presence of OHdefects in the quartz structure (Rossman, 1988). Also characteristic is a broad band with a maximum near 3400 cm-1, which often overlaps the absorption bands mentioned above, that is related to the presence of The proper use and limitations of IR spectroscopy for identifying natural versus synthetic amethyst of various types have been investigated, focusing on the region 3800–3000 cm-1. The presence of absorption bands at approximately 3680, 3664, and 3630 cm-1 unambiguously proves artificial origin, but only for samples grown in near-neutral NH4F solutions. Conversely, there are no unambiguous diagnostic features in the IR spectra of the more commercially significant synthetic amethyst grown in alkaline K2CO3 solutions. Nevertheless, previous investigators have found potential diagnostic value in absorption bands at approximately 3595 and 3543 cm-1. Although the 3595 cm-1 band is not found in the spectra of synthetic amethyst, it also is frequently absent from those of natural amethyst. The 3543 cm-1 band is found in the vast majority of synthetic amethysts grown in alkaline solutions, but this band also is sometimes present in natural amethyst—so it provides only tentative evidence of synthetic origin. Moreover, the 3543 cm-1 band is absent from some varieties of synthetic amethyst. The unambiguous identification of natural versus synthetic amethyst therefore must be based on a combined examination of the IR spectra, internal growth structures (including twinning), and inclusions.

Elastic characterizations of α-GaPO4 single crystals grown by the flux method

Transparent gallium orthophosphate single crystals with the α-quartz-type structure, α-GaPO4, were obtained using the high temperature solution growth technique in a Li2O–3MoO3 flux. A first measurement of several elastic constants Cijkl of the millimeter-size α-GaPO4 piezoelectric single crystals obtained is reported. The elastic constants were computed from the resonance frequencies of the thickness vibration modes measured, at room temperature, in plates polished in these crystals. These resonances were excited either by an electric field normal to the plates (conventional thickness excitation) or by a field parallel to the surface of the plates (lateral field excitation). As usual, the elastic constants were extracted using the formulae given by the corresponding one-dimensional theories of thickness vibration of piezoelectric plates. The measured elastic constants Cijkl of the flux-grown α-GaPO4 were generally found to be higher than those measured with α-GaPO4 crystals grown using the hydrothermal technique. This is most probably related to the extremely weak concentration of OH impurities existing in the crystals obtained using this flux-growth method.

Physical characterizations of α-GaPO 4 single crystals grown by the flux method

Hexagonal gallium orthophosphate crystals have been obtained by spontaneous nucleation using the slow cooling method from X₂Mo₃O₁₀ fluxes with X=Li, K. Infrared transmission measurements have revealed samples without significant hydroxyl groups and thermal analyses have pointed out the total reversibility state of the phase transition α-quartz GaPO₄ harr β-cristobalite GaPO₄. The first measurement of several elastic constants made on α-GaPO₄ material grown with the flux technique, using plates of simple orientations, was undertaken. The values found for these constants were slightly higher to those measured on hydro-thermally grown GaPO₄ crystals.

Piezoelectric properties of SixGe1-xO2 crystals

We report a first measurement of several elastic, piezoelectric, and dielectric characteristics of Si0.93Ge0.07O2 crystals. This was made using the thickness modes of plates of several simple orientations, using normal and/or lateral excitation. Corrections accounting for energy trapping effect (finite electrode dimension and mass loading) or stray capacitances were made after the measurements when partially electroded plates were used. The most interesting features of SixGe1-xO2 crystals already demonstrated are mainly the extremely reduced OH concentration, the existence of compensated cuts, the larger piezoelectric constants and the increased temperature of the alpha-beta phase transition.

Hydrothermal growth of piezoelectric crystals homeotypes of α-quartz

Growth and study of α-SiO2, AlPO4, GaPO4 and α-GeO2 single crystals with quartz structure are realized. Comparison of the crystal growth conditions (influence of solvents, T-P parameters, seed sizes and orientations, etc.), crystal quality (controlled by Polarized microscopy, IR-spectroscopy, X-ray topography, etc.), and piezoelectric properties in this material family have allowed to allocate and explain the main features on chemical side of hydrothermal crystal growth and physical properties of grown crystals. By this way during last years growth conditions were optimized and new growing solutions for α -quartz homeotype crystals were found. More interesting results, as some piezoelectric properties of GaPO 4 and α-GeO2, such are coupling coefficient and piezoelectric constants, were observed to be higher then the α-quartz one. The study and development of new techniques of hydrothermal crystal growth for GaPO 4 and α-GeO2 single crystals open opportunities for the synthesis of new α-quartz homeotype crystals with optimum properties for application in piezo-engineering.