Yasukazu Murakami

Microstructural changes associated with the martensitic transformation from cubic (parent phase) to trigonal (R phase) which occurs with decreasing temperature in Ti50Ni48Fe2 have been intensively studied by in-situ electron microscopy. Although the parent phase shows a characteristic microstructure with small domains, which are due to lattice modulation as a precursor to the transformation, their temperature dependence is contrasted with that of domains which appear below the transformation tem

Long-period structures with 32- and 36-fold periodicity to the original unit lattice distance were observed in a perovskite manganese oxide ${\mathrm{Bi}}_{0.2}$${\mathrm{Ca}}_{0.8}$${\mathrm{MnO}}_{3}$ at around 130 K, in addition to the one with fourfold periodicity. Quantitative electron diffraction profiles were measured for the long-period structure, where the intensity of superlattice reflections was observed to increase with increasing scattering angle due to static strain. This result ga

Behaviors of magnetic domains with cooling in a Ni51Fe22Ga27 ferromagnetic shape memory alloy were examined by electron holography and Lorentz microscopy. A peculiar meshy pattern was observed in the Lorentz microscope image of the parent phase, being concurrent with the anomaly in the thermomagnetization curve. The meshy pattern was found to stem from the heavily bent lines of magnetic flux. The dramatic change in the magnetic domains is presumably due to some intrinsic magnetic instability tha

Direct magnetization measurements from narrow, complex-shaped antiphase boundaries (APBs; that is, planar defect produced in any ordered crystals) are vitally important for advances in materials science and engineering. However, in-depth examination of APBs has been hampered by the lack of experimental tools. Here, based on electron microscopy observations, we report the unusual relationship between APBs and ferromagnetic spin order in Fe70Al30. Thermally induced APBs show a finite width (2-3 nm

It is known that the cubic (parent phase) to trigonal (R-phase) martensitic transformation is accompanied by some precursor phenomena in the parent state, such as appearance of weak diffuse scattering, although the mechanism is not clear. In the present work, the structural modulation in the parent phase was analyzed both in the real and reciprocal spaces by electron microscopy with a recently developed omega-type energy-filter and imaging plates. Some essential differences in characters were ob

Precursor effects of martensitic transformations in two well-known shape memory alloys, Ti50Ni48Fe2 and Ti50Pd34Fe16, were studied extensively by energy-filtered electron microscopy, including in-situ observations, and high-resolution electron microscopy. Energy-filtered dark-field images, where weak diffuse scattering was utilized, clearly showed the microstructure in the premartensitic state of Ti50Ni48Fe2. Tiny domains observable in this state were close to spherical rather than thin and slen

The crystallography of B2→7R stress-induced martensitic transformation in a Ni-37.0 at%Al alloy was studied using single crystals. The experimental results were compared with predictions of the phenomenological crystallographic theory. The simultaneously measured habit planes and the orientation relationship between parent and martensite showed excellent agreement with the theory, for the lattice invariant shear of faulting on the basal plane. Thus, the phenomenological crystallographic theory w