Multiferroic phase transition near room temperature in BiFeO3 films.

In multiferroic BiFeO(3) thin films grown on highly mismatched LaAlO(3) substrates, we reveal the coexistence of two differently distorted polymorphs that leads to striking features in the temperature dependence of the structural and multiferroic properties. Notably, the highly distorted phase quasiconcomitantly presents an abrupt structural change, transforms from a standard to a nonconventional ferroelectric, and transitions from antiferromagnetic to paramagnetic at 360±20 K. These coupled ferroic transitions just above room temperature hold promises of giant piezoelectric, magnetoelectric, and piezomagnetic responses, with potential in many applications fields.

Experimental and theoretical study of electron density and structure factors in CoSb3.

We refine two low-order structure factors of the skutterudite CoSb3 using convergent beam electron diffraction. The relatively large unit cell of this material causes the disks to overlap and introduces a series of challenges in the refinement procedure. These challenges and future work-arounds are discussed. The refined structure factors F200 and F600 are compared to X-ray diffraction and density functional calculated values, the latter calculated using two different functionals. Both relaxed and experimental lattice parameters are tested to explicitly highlight the impact of the lattice geometry and atomic position on the structure factors.

Quantitative electron diffraction evidence for one-dimensional ordering in magnetite above the Verwey transition.

Energy-filtered electron diffraction and three-dimensional reciprocal lattice mapping was used to study the nature of diffuse scattering in magnetite above the Verwey transition temperature. Characteristic Huang scattering associated with a single molecular polaron is observed at room temperature. As the temperature is lowered, the experiment shows narrowing of diffuse scattering in the (001) directions and additional ringlike diffuse scattering at q approximately 0.8, which suggests the presence of one-dimensional structures above the Verwey transition. Experimental measurements of temperature-dependent correlation lengths and diffuse scattering intensity indicate an increase in the number and length of the one-dimensional structure as the temperature is cooled toward the transition. This study demonstrates the electron sensitivity to atomic displacement and the quality of electron diffraction data for studying phase transition in complex materials.

Experimental measurement of electron diffuse scattering in magnetite using energy-filter and imaging plates

We have measured the diffuse scattering in magnetite as a function of temperature using the LEO 912Ohms energy-filtering electron microscope and the imaging plates. This study takes the advantage of the Koehler illumination system, energy filtering and the imaging plates for recording electron diffraction pattern over a large dynamic range. The experiment clearly shows a quantitative change in diffuse scattering distribution, which has the characteristics of one-dimensional ordering. This study clearly demonstrates the possibility for the quantitative study of diffuse scattering using electron diffraction.