Autoradiographic Investigations on the Incorporation of Ca Ions in KCl Crystals during Kyropoulos Growth

Ca doped KCl crystals were grown by the Kyropoulos method. 10⁻⁵ to 10⁻³ mole fractions of Ca (as CaCl₂ with a small amount of Ca-45 (β-emitter)) were added to the melt. By autoradiography of suitable cleavage planes the incorporation of the Ca ions was found to take place preferentially in a periodic manner parallel to the solid liquid interface. In the case of a rotating seed there is a segregation process in which only one zone of maximum Ca content is built up like a helix throughout the whole crystal, the axis being identical with the growth axis of the crystal and the slope of the helix corresponding to the growth rate per seed rotation, this leading to striations of long range periodicity on vertical cleavage planes. In the case of a non-rotating seed there is a different segregation process including a periodical incorporation too, but in discrete layers of relatively small separation parallel to the solid liquid interface in short range periodicity. Explanations for the segregation phenomena are given in terms of periodically varying effective growth rates related to periodic temperature fluctuations in the neighbourhood of the solid liquid interface.     

Zur Kristallographie von Doppelsalzen aus Calciumsulfat und Natriumsulfat

In the course of investigating a special slurry problem in the Na₂SO₄ production metastable double salts of calcium sulphate and sodium sulphate were detected (Emons, Stegmann). In this paper it is reported on the properties of these compounds and their decomposition products, determined by microscopic, X-ray, thermoanalytic, and IR-spectroscopic methods.     

Züchtung und Morphologie von Einkristallen aus Gadoliniummolybdat,einer ferroelektrischen und ferroelastischen Substanz

Czochralski-grown crystals of Gd₂(MoO₁)₃, usually rod-shaped, show growth ridges and small crystal faces. Due to this growth morphology a decision is made for the space-group P4 2₁m for the paraelectric modification between those spacegroups otherwise proposed by X-ray methods. Etching reveals a striation-like domain structure and dislocation etch-pits.     

Umwandlung des Fe3S4 von Fd3m nach Pa3, P4/nmm bzw. P63/mmc beim hydrothermalen Prozeß

A hydrothermal process of precipitating iron sulfide gives rise to greigite (space group: Fd3m), pyrite (Pa3), mackinawite (P4/nmm) and pyrrhotite (P6/mmc), as the case may be. Greigite blended with pyrite is formed, when the autoclave for the hydrothermal process is cooled down not rapidly, but slowly from 192°C to room temperature. Greigite and pyrite here form partially a solid solution. A mechanical mixture of greigite-mackinawite and that of greigite-pyrrhotite appear in the hydrothermal process above and below 192°C, respectively. Pure greigite is produced only by rapid quenching of the reaction tube from 192°C, to 10°C.     

Single crystal synthesis and properties of lithium-gallium-, lithium-aluminium-oxide and mixed compounds (I) growing of LiGaO2-, LiAlO2- and LiAlxGa1−x crystals from fluxes

LiGaO₂ forms a single eutectic with PbO/B₂O₃ (molar ratio 9:4). A nearly linear slope of the liquidus curve is followed by a steep rise of the temperature coefficient of solubility. The solvent power at 1300°C is 0.35 g LiGaO₂/g PbO, B₂O₃; from 1000 to 1300°C there exist only poor differences in solubility of LiGaO₂ and LiAlO₂ in PbO/B₂O₃. LiGaO₂ crystals up to 1 p in weight grew spontaneously by slow cooling from fluxes or by evaporation of the solvent, those of about 1–1.5 p from seeds by cooling stirred fluxes. LiAlO₂ crystals are essentially smaller (6 mm). – By partial substitution of Ga₂O₃ by Al₂O₃ mixed crystals LiAl_xGa_1−xO₂ result. In the case of x ≦ 0.5 the coefficient of segregation remains ≦1. The al concentrations along the polar axis decrease by more than 25 p.c., perpendicular to [001] they keep constant till to the crystal surface. – Crystals show hypermorphism from mm2 to mmm. With high initial exceedings only {110} and {011}, with lower ones also {120}, {130}, {210} and {310} as well as the reduced {100}, {010} combinations are observed. – LiGaO₂ crystals grow by nucleous, sceletal or faceted growth resp. during the cooling period. – Primarily at 1270°C formed nuclei up to 1150°C grow to critical dimensions (≈0.5 mm) and develop to the main branch along [001]. Primary branches deflect to [010]. The convex secondary branches intergrow along (110), often including flux. With decreasing temperature a new crystallisation front is formed at the periphery leading to a stable faceted growth at about 1000°C.