We report the in situ microscopy observation of an unnatural phase of Ni, a highly strained hexagonal close-packed ͑hcp͒ form which we believe is stabilized by heteroepitaxial growth on the ͑001͒ face of MgO. We find that the nanosized hcp nickel islands transform into the normal face-centered cubic structure when the size of the islands exceeds a critical value ͑about 2.5 nm thick with a lateral size of ϳ5 nm͒. The structural transition proceeds via a martensitic change in the stacking sequence of the close-packed planes. The formation of hcp Ni nanostructures with an unusually large crystallographic c / a ratio ͑ϳ6% larger than ideal hcp͒ is very interesting for spintronic and recording applications where large uniaxial anisotropies are desirable.

A high coercivity of up to 5.1 kOe was induced in a large-grained CoFe 2 O 4 powder after milling for a short time ͑1.5 h͒. It was found that the initial grain ͑particle͒ size played an important role in the microstructural evolution and in the magnetic properties of the milled CoFe 2 O 4 materials. The milling-induced microstructural evolution was analyzed using x-ray diffraction and transmission electron microscopy. The results indicated that the milling-induced high coercivity was associated with the highly-strained and defective microstructure. The enhancement in magnetic anisotropy was observed in large-grained CoFe 2 O 4 after milling, which might be mainly attributed to the stress anisotropy. In order to understand the coercivity mechanisms, detailed magnetic studies were carried out by the investigation of the field-dependent magnetization ͑demagnetization͒ behaviors and the magnetization reversal processes based on both the micromagnetic model and the phenomenological model. The results revealed that a domain wall pinning-controlled mechanism was responsible for the millinginduced high coercivity in CoFe 2 O 4 materials.

We demonstrate for the fist time that small-angle neutron scattering can be used as a direct and accurate method to determine the temperature dependence of the unperturbed dimensions of a polymer. The sensitivity of the technique arises from the remarkable accuracy with which the random walk model can be used to describe the single-chain structure factor, and enables us to detect changes in the polymer radius of gyration of less than 0.5%. We present results for molten polyethylene and verify the accepted value of the temperature coefficient of thermal expansion.

Layered first-row transition metal (cobalt, chromium, iron, manganese and nickel) oxyhydroxides were investigated for electrocatalytic behaviors in HER, OER, and ORR.