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.
The crystal structure of fl-beryllia has been determined from X-ray powder data collected at 2100 °C The structure is tetragonal with a = 4.75 and c--2.74 A, and contains four molecules of BeO in the unit cell. The density is 2.69 g.cm -3. The structure is related to rutile, TiO~, in that the oxygen arrangement is identical. Beryllium atoms are in tetrahedral sites. The space group is P4~./mnm, and the oxygen and beryllium atoms are in sites 4(f) and 4(g) respectively with xo =0.310 and XBe --0"336.
Single crystals of beryllia have been grown by two methods. One method exploits the hightemperature reversible reaction B e 0 + HzO % Be(OH)2. The other is a flux method, in which B e 0 is dissolved and precipitated as single crystals in a lithium molybdate flux. Characteristics and remaining problems of the two methods are discussed, and the crystals produced are described.
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, ε33T/ε0∼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.
Single crystals of B e 0 were irradiated by high energy (2 1 MeV) neutrons to doses of 102" t o 6:. 102O nvt a t 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 reflect,ions each composed of a sharp and a broad component. The sharp component is attributed to t,he matrix crystal volume, which is expanded by a random distribution of point defects. The broad component is attributed t o t h e presence of interplanar clusters lying parallel to the basal plane. This structure showed little change below 800 O C with short-term anneal. Between 800 and 1600OC there was nearly complete recovering of line breadth and lattice constants. The annealing data indicate ( I ) removal of the point defects, and (2) some growth of cluster size, during thermal annealing.BeO-Einkristalle wurden mit Neutronen hoher Energie ( 2 1 MeV; Dosis lozo bis 6 >' lo2" n'eutronen pro Zeiteinheit) bei tiefen Temperatnren (< 100 "C) best,rahlt. Der EinfluB dieser Bestrahlung auf die Kristallstruktur wurde mit Hilfe der Rontgenbeugung und Messungen der Greuzflachenwinkel 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 mird dem Matrixvolumen zugeschrieben, das durch eine statistische Verteilung von Punktdefekten gedehnt ist. Die breite Komponentc wird durch die Anwesenheit von interplanaren Anhaufungen erklart, die parallel zur Basisflache liegen. Diese Struktur zeigt geringe Veranderungen bei kurzzeitiger Temperung unterhalb 800 O C . Zwischen 800 und 1600 "C erholen sich die Linienbreiten und Gitterkonstantm nahezu vollstandig. Die Temperungsergebnisse zeigen 1) eine Beseitigung von Punktdefekteu und 2) ein gewisses Aniva.chsen der GroBe der Anhaufung wahrend der Temperung. 2, Private communication from J. M. McKenna, Philips Petroleum Co., Idaho Falls. 3, Private communication from C. G. Collins, General Electric Co., Cincinnati, Ohio. Idaho. 16'
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