Субструктура интерметаллического соединения Cu-=SUB=-3-=/SUB=-Sn в тонкопленочном состоянии

The crystalline structure of intermetallic Cu_3Sn synthesized by successively condensing thin layers of copper and tin on a substrate at 150°C has been studied. Cu_3Sn compound exists in a very narrow homogeneity range and has a long-period close-packed ordered D0_19 superstructure. It has been found that the crystal lattice exhibits many slip traces associated with dislocation motion. The dislocation motion is due to the stressed state of the crystal, which can be characterized as uniform extension. Electron micrographs show that slip traces in the Cu_3Sn crystal are parallel to the ( $$\bar {1}\bar {1}21$$ ) and ( $$11\bar {2}1$$ ) planes belonging to pyramidal slip system II, which is a main slip system along with pyramidal and basal ones. Slip traces result from the motion of partial dislocations, as indicated by the amount of slip, which is equal to half the interplanar distance. Since the crystal is ordered, slip is accomplished by a pair of superpartial dislocations and a slip trace may be a superstructural or complex stacking fault.

On the praseodymium + oxygen system

An isobaric survey of the system praseodymium oxide + oxygen has been made at oxygen pressures between 0 and 1 atm and in the temperature range 200 to 1150 °C. The derived isobaric sections enable a three-dimensional phase diagram (pressure, temperature, composition) to be constructed with considerable certainty and detail for the composition range PrOj.gg to PrOj.g*. Reasonable extensions to cover the complete range between the sesquioxide and dioxide are proposed, and a projection of the diagram on to the temperature-composition plane is presented. At lower temperatures several discrete, ordered phases of narrow homogeneity range exist. These constitute an homologous series P r„02n_2, with n = 4, 7, 9 ,1 0 ,1 1 ,1 2 , oo. At higher temperatures two wide-range solid solutions obtain: <r, a body-centred cubic phase with a maximum composition range ca. PrOj.gQ to PrOj.yo; and a, a face-centred cubic phase of composition P r O ^ to P r 0 2. The fields of stability of the various phases are defined and the ambient conditions at many invariant axes (peritectoid and eutectoid) enumerated. Miscibility gaps with upper consolute points are exceptional; order-disorder peritectoid transformations are common. Hysteresis in phase transformations is confirmed, and the results further demonstrate the existence of metastable states in phase reactions involving an increase in structural order. The appearance of these pseudo-phases and the nature of non-stoichiometry is explained in terms of a plausible model invoking microdomain texture in defect solids. This model is believed to be appropriate for other non-stoichiometric systems also. Earlier experimental data on the system are examined, and found to be consistent with the present results.