Abstract
Summary Layers of metallic barium were obtained by volatilizing the metal in the (evacuated) electron diffraction apparatus and depositing it on a flat polished copper disc. Depending on the conditions of evaporation (temperature), they show either random orientation of the crystallites, or a preferential orientation characterised by a [111]-direction perpendicular to the plane of the supporting disc. The oriented layers, on oxidation, yield likewise oriented oxide layers. In these latter, the normal to the support is nearly parallel to a [110]-direction of the oxide lattice, deviating from it by about 10°–15° towards [100]. It is thus found that a direction of closest packing of the metal atoms in the face-centred oxide lattice (i.e. a [110]-direction) is closely parallel to a corresponding direction in the body-centred metal lattice (i.e. a [111]-direction). The relationship is further discussed in connection with that found by Mehl, McCandless and Rhines to occur between FeO and Fe on oxidation of a single crystal of iron. It was found that the [11 Indirection in the oriented barium layers, formed under conditions of oblique incidence of the vapour beam, deviates slightly from the normal to the supporting disc towards the direction of the incident beam, a behaviour analogous to that observed previously with layers of calciumfloride, deposited in vacuum from the vapour.
Published Version
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