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Graphite crystals grown from hypereutectic solutions of carbon in iron were examined microscopically with a view to establishing the mechanisms of growth. It is proposed that nucleation occurred on a second phase which had been retained in some crystals extracted from the molten solution. The perfection of the crystals, which is compared with that of naturally occurring and pyrolytic graphites, is a function of the extent of decomposition of this second phase and the impurity content of the melt.

Single crystals of BeO were irradiated by high energy (≧ 1 MeV) neutrons to doses of 1020 to 6 × 1020 nvt at low temperature (< 100 °C). The crystal structure effects of irradiation were examined by X-ray diffraction and measurement of interfacial angles between crystallographic faces. The diffraction patterns are characterized by duplex reflections each composed of a sharp and a broad component. The sharp component is attributed to the matrix crystal volume, which is expanded by a random distribution of point defects. The broad component is attributed to the presence of interplanar clusters lying parallel to the basal plane. This structure showed little change below 800 °C with short-term anneal. Between 800 and 1600 °C there was nearly complete recovering of line breadth and lattice constants. The annealing data indicate (1) removal of the point defects, and (2) some growth of cluster size, during thermal annealing. BeO-Einkristalle wurden mit Neutronen hoher Energie (≧ 1 MeV; Dosis 1020 bis 6 × 1020 Neutronen pro Zeiteinheit) bei tiefen Temperaturen (< 100 °C) bestrahlt. Der Einflus dieser Bestrahlung auf die Kristallstruktur wurde mit Hilfe der Rontgenbeugung und Messungen der Grenzflachenwinkel zwischen kristallographischen Flachen untersucht. Die Beugungsbilder sind durch Doppelreflexe charakterisiert, von denen jede aus einer scharfen und einer breiten Komponente zusammengesetzt ist. Die scharfe Komponente wird dem Matrixvolumen zugeschrieben, das durch eine statistische Verteilung von Punktdefekten gedehnt ist. Die breite Komponente wird durch die Anwesenheit von interplanaren Anhaufungen erklart, die parallel zur Basisflache liegen. Diese Struktur zeigt geringe Veranderungen bei kurzzeitiger Temperung unterhalb 800 °C. Zwischen 800 und 1600 °C erholen sich die Linienbreiten und Gitterkonstanten nahezu vollstandig. Die Temperungsergebnisse zeigen 1) eine Beseitigung von Punktdefekten und 2) ein gewisses Anwachsen der Grose der Anhaufung wahrend der Temperung.

Compositional and lattice constant control of non-magnetic garnet substrates are required for suitable lattice matching with epitaxially deposited magnetic thin film. Suitable substrates for this purpose are the simple and mixed rare earth garnets. Lattice constants were obtained on Czochralski grown crystals by conventional x-ray diffraction powder techniques with a precision of ± .0005Å. An x-ray fluorescence method was developed to determine crystal composition with a precision of ± 0.5 percent. The precision with which a can be determined indirectly by x-ray fluorescence is ± 0.0082Å, which is comparable with that from direct measurement.

Chemical etching behaviour of BeO crystals was investigated for selected etchants ranging from basic to acidic in nature. Surface-emergent defects (dislocations, enclosed platinum crystals, point-defect concentrations, surface mechanical damage, twin boundaries) give rise to recognisable etch figures that are characteristic of etchant, defect type, and orientation of emergence face. Gross etching rates (in the absence of surface-emergent defects) are strongly anisotropic for both basic and acidic etchants, reflecting the crystallographic polarity of the BeO crystal structure; intermediate etchants give nearly isotropic etching. The details of gross and figure etching are described.

The thermal conductivities of three single crystals of BeO have been measured from 2 to 300 K. Phonons carry the heat at all temperatures. At 300 K the conductivity is 3.7 W/cm K, which is slightly less than that of copper. In the purest sample the maximum conductivity occurs at 45 K where it is 137 W/cm k, and at temperatures below 10 K the conductivity is limited by boundary scattering. The anisotropy in the conductivity of this hexagonal material is 20% or less.

Piezoelectric, dielectric, and pyroelectric measurements were made on hexagonal BeO crystals grown in molten lithium molybdate flux. The piezoelectric constant d33∼0.24×10−12 C/N, e33T/e0∼7.6, and the average free pyroelectric constant in the range −196° to 25°C is −3.4×10−10 C/cm2 °C. The sound velocity perpendicular to the polar axis is 12 000 m/sec. Although no absolute identification of crystal planes was made, it was concluded from the sign of the piezoelectric constant d33 that the oxygen side of the closely coupled Be—O layer is that of principal growth and etch. Polarity of the crystal structure is reflected in typical crystal growth habits and in characteristic etch patterns which are described.

The domain structures observed in low magnetization compositions of iron garnet films grown by chemical vapor deposition (CVD) on rare earth gallium garnet substrates are consistent with a recently‐developed stress model for epitaxial films1. By utilizing lattice matching, bubble domains have been formed in positive magnetostriction materials in compression as well as negative magnetostriction materials in tension. The film/substrate mismatch characteristics can be evaluated by comparing domain structures, X‐ray measurements of the strained lattice spacings, and the predictions of the stress model. Requirements and restrictions on the mismatch of film/substrate lattice constants and thermal expansions are discussed for the iron/gallium garnet system.

Experimental results are reported on the coupling between electromagnetic signals and acoustic waves in beryllium oxide crystals via interdigital transducers deposited on a natural y face of a BeO crystal. The transducers are oriented to propagate acoustic waves along the z axis.

THE development of β-beryllia1 has been observed in the electron microscope. Fine chips of beryllium oxide obtained by grinding single crystals in a mortar and supported on a carbon substrate were examined in an EM–6 electron microscope. Most of the transparent chips fracture along prism planes and these yielded single crystal diffraction patterns which were readily indexed as the normal hexagonal structure of α-beryllia. Transformation to the high-temperature form was accomplished by defocusing the illuminating electron beam and allowing a more intense beam to strike the sample. This develops a finely shattered texture in the crystal. The evidence that the tetragonal structure of β-beryllia is formed is indicated by the appearance of new rings or diffraction spots from β-beryllia that are superimposed on the spot diffraction pattern of single crystal α-beryllia. In particular there are observed the (110) and (310) reflexions of β-beryllia with d-spacings agreeing within experimental error with those previously reported1; simultaneously the (002) of α-beryllia is commonly absent. Occasionally extra diffraction rings appear; these can be indexed if one presumes that beryllium carbide is formed by reaction between the beryllium oxide and the carbon substrate.