Samuel S. Shinozaki

Antiferromagnetic Transition in γ‐Phase Mn Alloys

Specific heat measurements on Mn‐rich Mn‐Cu alloys reveal first‐order antiferromagnetic phase transitions at around room temperature and above. Magnetic entropy increases with Mn content but in all alloys it is smaller than would be expected from localized spins. The same is true of an equiatomic FeMn alloy. However the specific heat exhibits a well‐defined cusp at 475°K, indicating a transition of second or higher order. By extrapolating the Mn‐Cu results to pure Mn, the thermodynamic properties of γ‐Mn in the region of the transition are derived.

Tandem deposition of small metal particle composites

A new method for preparing small metal particle composites (cermets) is described. It consists of many sequential depositions on a substrate of small amounts of a metal and an insulator from separate deposition sources. Under certain conditions, this method provides composites which, for metal volume fractions of less than about 0.5, consist of metal spheres with a very narrow size distribution embedded uniformly in the insulating matrix. In addition to the improved morphology of the composites, the new method also allows, for the first time, for control of metal particle size independent of metal volume fraction.

Direct observation and identification of long‐period structures of SiC by transmission electron microscopy

Transmission electron microscopy has been used for the observation of polytypes of SiC having very long periods. The periodicity of these structures can be observed from the direct resolution of structural lattice periods and from the diffraction patterns. The actual structures can be determined from the intensity distribution in the diffraction pattern, and this has been done for two of the structures. These have been identified as [(33)1632]3 or 303R and [(33)634(33)434]3 or 222R, two hitherto unknown structures. A mechanism for conveying the long‐distance information concerning the stacking order which leads to stabilization of the long‐period structures in SiC is suggested. This mechanism essentially involves a transformation from a basic structure of short period to accommodate a constraint from the surroundings.

Nucleation of Multiply Twinned Particles at an Early Stage of Vapor Deposition

The study of nuclei of Au deposited on NaCl substrates cleaved in the ultrahigh vacuum shows that most small deposits on the flat parts of the substrate are multiply twinned particles, whereas, at the cleavage steps there are epitaxial particles of definite shapes with either (100) or (111) orientation. From the dependence of the shape of small deposits on the magnitude of the interfacial interaction and from the stability of the multiply twinned particles, it is concluded that the predominant existence of multiply twinned particles is an indication of negligible interfacial interaction while the existence of epitaxial particles at the steps is due to the creation of nucleation sites by surface defects. The loss of epitaxy of Au on NaCl cleaved in an ultrahigh vacuum is explained as the result of negligible interfacial interaction between the deposits and substrates.

Studies of Au4X‐Ordered Alloys: Electron and Neutron Diffraction, Resistivity and Specific Heat

Micro‐, chemical and magnetic structures of ordered alloys Au4X, where X stands for various transition elements and their mixtures, have been studied using electron, x‐ray, and neutron diffraction. Specific heat and electrical resistivity measurements have been carried out for Au4Ti, Au4(Ti0.5Cr0.5)Au4V, Au4(V0.5Mn0.5)Au4Cr, Au4(Cr0.5Fe0.5), and Au4Mn. The magnetic form factors are given for Au4Cr and Au4Mn.

Lorentz Microscopy of Magnetic Domains of Single‐Crystal Films

Domain patterns of epitaxially grown iron single‐crystal films are investigated by the Lorentz microscopy technique. The width of 180° walls appear much wider than that of 90° walls. Double 90° walls and the fine structure of 180° walls, such as Bloch lines, etc., are observed.

Cleaving of MgO inside an Electron Microscope

A method for preparing clean surfaces of the (100), (111), and (110) orientations of MgO directly at the specimen chamber of an electron microscope and thin enough for transmission electron microscopy is described. The cleaving is accomplished by thermal shock due to a flash electron bombardment. The cleaved crystals are suitable as substrates for in situ observation of surface reactions like epitaxial growth. The cleavage mechanism is also discussed.

The nature of sialon joints between silicon nitride based bodies

Quite strong joints between silicon nitride based bodies have been made by incorporating a layer of aluminium and oxides between the bodies and heating in a nitriding atmosphere. The joints are resistant to thermal shock and maintain their strength at 1200° C. Microscopic, DTA and X-ray diffraction studies indicated that sialon phases are present in the joints, and that the bonding reaction involves the reduction of Si3N4 by aluminium and the subsequent renitriding of the resultant silicon, as well as the simultaneous nitriding of a portion of the aluminium. Transmission electron microscopy of a joint between hot pressed and reaction bonded silicon nitrides showed that 15R aluminium nitride polytype sialon was present on the reaction bonded side of the joint and ß′-sialon on the hot pressed side.

Unusual microstructures in TiO2 ceramic pellets with asymmetrical electrical conductivity

Ceramic pellets of TiO2 (rutile), with embedded Pt wire electrodes, have been heat treated in a manner that changed the normal electrical properties of rutile at room temperature from those of an insulator to those of a semiconductor with rectifying characteristics. This change in electrical properties was accompanied by the development of unusual microstructures in the rutile grains which were analyzed by a combination of techniques including transmission electron microscopy and scanning transmission electron microscopy. These analyses indicated that, under the applied conditions of heat treatment, Pt diffused into the rutile and reacted initially with the TiO2 at oxygen vacancy sites to form point‐defect agglomerates and that these point defects blocked the normal formation of crystallographic shear planes. As the process proceeded by continued Pt diffusion, thin planar precipitates of PtTi3 were formed in epitaxial relation to the surrounding rutile matrix.

Electrical rectification caused by lamellar microstructures in platinum‐doped TiO2−x ceramics

A heat treatment combining cyclic oxidation/reduction with an applied electric field is described that enhances the diffusion of Pt into TiO2−x ceramics and causes a reaction product of PtTi3 to be formed. The PtTi3 forms as lamellar microstructures within the TiO2−x rutile grains. The ceramics produced by this heat treatment have markedly altered electrical properties showing room‐temperature conductivities increased several orders of magnitude and asymmetrical conductivity (rectification) characteristics.