The Heusler-type alloy Ni 2ϩx Mn 1Ϫx Ga exhibits well defined shape memory properties in a ferromagnetic state, which means that the martensitic transition temperature is lower than the Curie point of this material. The change of composition makes these characteristic temperatures approach each other. To study this behavior, the measurements of specific heat, ac magnetic susceptibility, and dc resistivity were performed. The phase diagram of the cubic ferromagnet describing possible structural and magnetic transitions is obtained theoretically. This diagram is compared with experimental data on Ni 2ϩx Mn 1Ϫx Ga. An estimate is given of the magnetic-field influence on the temperature of martensitic transformation in the studied alloys.

Hydrothermally synthesized BaTiO3 powders with nanoscale-sized particles were densified by microwave sintering. A sintered sample of the nanopowder fabricated by hydrothermal synthesis has a high piezoelectric constant d33 due to fabrication by microwave sintering. The maximum value of the piezoelectric constant d33 of a specimen fabricated by microwave sintering was approximately 350 pC/N for a small grain size of 2.1 µm. Detailed microstructures of the samples were observed by transmission electron microscopy (TEM) and scanning electron microscopy/electron backscattered diffraction analysis/orientation imaging microscopy (SEM/EBSD/OIM). The size of ferroelectric domains in the samples showing superior piezoelectric properties was less than 50 nm. SEM/EBSD/OIM observations revealed that the fraction of random boundaries was higher by approximately 10% in microwave sintered samples than in conventionally sintered ones. It is suggested that the small size of domain and the higher fraction of random boundaries might be responsible for the excellent piezoelectric properties of small grains, which can partially be attributed to domain size.

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A lead-free barium titanate (BaTiO3) ceramics with a high density and a large piezoelectric constant, d 33, as manufactured at 1320°C by microwave sintering, using a pure fine powder with a particle size of 100 nm produced by hydrothermal synthesis. The density of the ceramic with a 3.4 µm grain size was more than 98.3% of the theoretical value. The ceramic after poling had a dielectric constant of ε 33 T /ε 0 =4200, an electromechanical coupling factor planar mode of k p =36% and d 33 =350 pC/N. The value of d 33 is the largest one ever reported for lead-free BaTiO3 ceramics.

This article presents a review of recent important developments in the field of intelligent material systems. Intelligent material systems, sometimes referred to as smart materials, can adjust their behavior to changes of external or internal parameters analogously to biological systems. In these systems, sensors, actuators and controllers are seamlessly integrated with structural materials at the macroscopic or mesoscopic level. In general, sensors and actuators are made of functional materials and fluids such as piezoelectric materials, magnetostrictive materials, shape memory alloys, polymer hydrogels, electro- and magneto-rheological fluids and so on. This article is specifically focused on the application of piezoelectric materials, magnetostrictive materials and shape memory alloys to intelligent material systems used to control the deformation, vibration and fracture of composite materials and structures. This review article contains 188 references.