Dimensional and X‐Ray Diffraction Changes in Irradiated Single Crystal BeO

Abstract

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'

Phase stability, swelling, microstructure and strength of Ti3SiC2-TiC ceramics after low dose neutron irradiation

“…4,26,40,41After irradiation, brighter intragranular regions in Ti 3 SiC 2 were observed in orientations parallel and normal to the a-axis.Figures 5(e) and (f) show higher magnification images of the "intragranular regions" that have the same contrast as TiC(1-x) in the as-received material. Tallman et al observed basal plane ½<0001> strain-field nanometric dislocation or antisite loops at 0.1 and 0.4 dpa 17,35,36. This is consistent with the planar component to defects in hcp ceramics.…”

“…33,34 In BeO, data extrapolated to T irr ~400°C revealed Δc/c values that saturated at ~2.5%, while Δa/a was in the order of -0.1%. 33,34 The theories to explain the c-axis increase in BeO show similarities to Ti 3 SiC 2 ; Sabine, Austerman and Miller et al all proposed planar defect clusters but were unable to agree on configuration, but the reported size (7.5 nm) was consistent with low dose microstructures seen by Tallman et al 17,35,36 As T irr increases, volumetric swelling (ΔV/V) due to LP changes in BeO were reduced due to increased defect mobility (which promoted point defect recombination), and lattice swelling saturated to values that were dependent on temperature, because defects were thermally dissipated as they were produced. 33,34 LP values in Figure 4 suggests that in Ti 3 SiC 2 , this begins from T irr ~ 550-700°C, which was unfortunately below the radiation temperature in this study, and is the subject of future isochronal annealing.…”

Microstructure of Bulk Nanomaterials Determined by X‐Ray Line‐Profile Analysis

“…For more details about diffuse scattering of point defects see [107][108][109][110][111][112][113][114][115][116].…”

Diffraction by crystals with planar faults. I. General theory

“…Many observations of intensity maxima displaced from reciprocal-lattice-point positions have been reported and discussed in the literature. Notable examples include the diffuse scattering associated with heavy radiation-damage effects in close-packed metals and oxides (Austerman & Miller, 1965;Keating, 1968;Nimura, 1955) and the diffuse scattering associated with the fie) transformations of various Ti and Zr alloys (Moss, Keating & Axe, 1973;Borie, Sass & Andreassen, 1973). In each case an analysis of the scattering in terms of the model we have used here provides an immediate indication of the type of fault involved and the approximate frequency of occurrence of the fault.…”