2,089 publications from this institution
We show that the polycrystalline perovskite antiferromagnet Pr0.5Sr0.5MnO3 exhibits a giant anisotropic magnetostriction (λt=1.5×10−3 at T=25 K and H=14.2 T) contrary to much smaller λt (<0.1×10−3) found in most other three-dimensional manganites. The value of λt decreases rapidly as the Néel temperature is approached from below, but an unusually high value of λt is also found below the ferromagnetic Curie temperature. We suggest that the magnetic-field-induced antiferromagnetic-to-ferromagnetic transition is accompanied by a structural transition from orthorhombic to tetragonal symmetry and attribute the giant anisotropic effect to the preferential growth of the orbital disordered tetragonal (ferromagnetic) domains along the field direction in the eg-dx2−y2 orbital ordered orthorhombic (antiferromagnetic) matrix.
Reaction of low surface area carbon with a mixture of urea and boric acid at 930 °C yields a composition close to BC 4 N with a graphitic structure. BC 4 N was characterized by electron energy loss spectroscopy, X‐ray photoelectron spectroscopy, transmission electron microscopy, Raman spectroscopy, and X‐ray diffraction. BC 4 N is a porous ceramic with a surface area of 428 m 2 · g –1 , and shows a CO 2 uptake of 40 wt‐%. The layered structure of BC 4 N involves a random distribution of boron, carbon, and nitrogen atoms and shows high thermal stability up to 1000 °C. A comparative analysis of the structure and properties of BC 4 N and graphene using first‐principles pseudopotential based density functional theoretical calculations is presented. The calculations predict it to be an insulator. The bulk modulus of BC 4 N exhibits an interesting dependence on the ordering of boron and nitrogen on the graphene lattice.
