G. Rosenstein

Hydrothermal preparation of barium titanate from barium-titanium acetate gel precursors

Abstract Clear, transparent gels of BaTi acetate have been prepared from titanium tetrabutylate (TBT), Ba acetate aqueous solution, isopropanol and acetic acid. Infrared spectroscopy and transmission electron microscopy (TEM) of such gels revealed linked clusters of polymer Ti oxyacetate with surface adsorbed Ba acetate. Spray dried Ti oxyacetate has been found to have the stoichiometric composition Ti 2 O 3 [CH 3 COO] 2 . Calcination of BaTi acetate gels to BaTiO 3 in air turned out to be a less favourable preparative route, because stable intermediate carbonate phases were formed. Corresponding to the high surface area and fine dispersion of Ba and Ti, BaTi acetate gels are higly reactive precursors for hydrothermal synthesis of BaTiO 3 . Nearly quantitative (> 99·7%) chemical reactions were obtained without using Ba excess at processing. TEM provided interesting information about the chemical mechanisms of hydrothermal processing.

X-ray structure investigation of lanthanum modified lead titanate with A-site and B-site vacancies

The validity of a perovskite structure model with A-site and B-site vacancies in the system PbO  TiO2  LaO1.5 was checked by X-ray structure investigations. The observed structure factors indicate that the proposed model with A-site and B-site vacancies holds in the range [¦A¦][¦B¦] ⩽ 1. Strong evidence was found that the lanthanum ions only enter the A-sites of the perovskite structure.

Telluride halides of gold

Abstract The preparation of four gold telluride halides—including hydrothermal syntheses—is described. Chemical and physical properties, including lattice parameters and thermal and chemical stabilities, are dealt with. The compounds AuXTe 2 ( X = Cl , Br , I ) exhibit metallic conductivity whereas AuITe is a semiconductor with an optical band gap of about 0.9 eV. Only a formal resemblance seems to exist with the analogous copper compounds.

Phase relationships in the gold-selenium system

Abstract The gold-selenium system has been investigated up to about 1000 ° C by D.T.A., X-ray powder, and single crystal diffraction patterns and, partially, vapour pressure measurements. The existence of two modifications of AuSe, α and β, has been confirmed. The unit cell relationships and relative stabilities of these—both monoclinic—are discussed. No other binary compounds seem to exist. The preparation of these phases, including hydrothermal synthesis, is dealt with. Single crystals of α-AuSe showed metallic conductivity. Besides the monotectic between gold and selenium at about 760 °C and 52 at.% Se, a second monotectic is formed at 963 °C and 15 at.% Se. A completed phase diagram is given.