Reducing Inversion Twinning in Single Crystal Growth of GaPO4

Gallium orthophosphate (GaPO₄) single crystals were grown by the reverse temperature gradient method from phosphoric acid solutions under hydrothermal conditions. Twins after (110) were studied by etching faces having been cut perpendicular to one of the twofold axes. Based on the determination of the twin boundary position as well as on the knowledge of the growth rates of different crystallographic forms, a few faces have been chosen to be quite promising for growing high‐quality GaPO₄ single crystals if they are offered at the referring seed crystal. From the characterization of the grown crystals conditions have been found, which may lead to the reduction of the inversion twin number during the growth process.     

Etch studies on GaPO4 single crystals

Etch figures on gallium orthophosphate (GaPO₄) crystals are presented for the {0 0 1}, {0 1 0}, , and {1 0 1} faces. Primarily they are used in detecting possibly occurring domains of twinning. Generally, the etch figures of GaPO₄ show similarities as well as differences compared to those of low-quartz modifications of SiO₂ and AlPO₄.     

Analysis of the morphology of hectorite by use of small-angle X-ray scattering

An analysis of the three-dimensional correlation function of small-angle scattering is applied for the direct determination of stereological parameters of hectorite samples. Beside characteristic lengths and volume fractions the specific order distances are given. The samples can be described by homogeneous particles of different order magnitudes up to the size of the secondary particles, which were estimated to have maximum dimensions of about 450 nm. Beside traditional stereological formulas, including the interpretation of the derivatives of the small-angle correlation function, the so-called transformed correlation function is applied in order to detect distinctive characteristic lengths. Received: 2 December 1999 Accepted: 9 March 2000     

Untersuchung von Wasser und Abwasser

Analytical and Bioanalytical Chemistry -     

Noise annoyance assessment of various urban road vehicle pass-by noises in isolation and combined with industrial noise: A laboratory study

Noise maps are diagnosis tools which represent the noise exposure situation using the energy-based index L_den (the day–evening–night level). Two major drawbacks may be attributed to noise maps: (1) energy-based indices only account for one acoustical factor (exposure level) that may give rise to annoyance; (2) combined exposures situations are left unframed.     

Application of small-angle scattering for the identification of small amounts of platinum supported on porous silica

Pt-porous glass catalysts have been studied by small-angle X-ray scattering. The catalysts have been prepared by impregnating two micro- or mesoporous glasses with 0.1 wt% of Pt. Two different pore systems of the catalyst supports have been generated and investigated: on the one hand, the mesoporous structure is formed by finely dispersed colloidal silica inside a macroporous glass. On the other hand, micropores are given by the porous glass itself. The pure supports and the supported catalysts have been investigated via chord length analysis for a selected range order, based on the analysis of the scattering intensity for relatively large scattering vectors (up to the upper limit of SAS). The obtained specific structure parameters of both supported catalysts like dispersion, specific metal surface areas, basic arrangement, size distribution and volume fraction of the metal particles basically differ with both pore systems.     

Growth of Gallium Orthophosphate Single Crystals under Hydrothermal Conditions

Gallium orthophosphate (GaPO₄) single crystals have been grown from phosphoric acid solutions under hydrothermal conditions. The crystals have been studied in terms of twinning because of the strong effect of this structural defect on the piezoelectric properties. The growth rates of individual faces have been compared to each other by considering the dipyramidal habit of the grown crystals.