We report a temperature-dependent Raman scattering investigation of thin film rare earth nickelates SmNiO 3 , NdNiO 3 and Sm 0.60 Nd 0.40 NiO 3 , which present a metal-to-insulator (MI) transition at T MI and an antiferromagnetic-paramagnetic Néel transition at T N . Our results provide evidence that all investigated samples present a structural phase transition at T MI but the Raman signature across T MI is significantly different for NdNiO 3 (T MI = T N ) compared to SmNiO 3 and Sm 0.60 Nd 0.40 NiO 3 (T MI ≠ T N ). It is namely observed that the paramagneticinsulator phase (T N < T < T MI ) in SmNiO 3 and Sm 0.60 Nd 0.40 NiO 3 is characterized by a pronounced softening of one particular phonon band around 420 cm -1 . This signature is unusual and points to an important and continuous change in the distortion of NiO 6 octahedra (thus the Ni-O bonding) which stabilizes upon cooling at the magnetic transition. The observed behaviour might well be a general feature for all rare earth nickelates with T MI ≠ T N and illustrates intriguing coupling mechanism in the T MI > T > T N regime.
The optimization of metal-matrix composite material is linked firstly with the intrinsic properties of the matrix and the reinforcement used and secondly with the reinforcement-matrix interfacial zone and the distribution/orientation of the reinforcement inside the metal-matrix. Flake powder metallurgy was used to fabricate graphite flake reinforced aluminum matrix (Al/GF) composites fabricated by vacuum hot pressing. Two types of aluminum powders morphology were used: spherical (AlS) and flake (AlF) powders. A higher thermal conductivity in the in-plane direction of the graphite flakes was obtained for Al/GF composite materials fabricated with aluminum flake powder. In addition to a better orientation of the GF in the flake aluminum matrix, a 3D puckered surface and plane surface are formed at the Al/GF interface in, respectively, AlS/GF and AlF/GF composite materials. Due to the morphology incompatibility between the graphite flakes and the spherical powder, the damaged inner structure of GF contributes to a limited enhancement of thermal conductivity in AlS/GF composite materials.
In order to obtain modulated martensite in our epitaxial Ni-Mn-Ga films, we tuned the composition by using a co-sputtering process.Here we present how the composition affects the variant distribution of the 14-modulated martensite at room temperature. The nature of such modulated martensites is still strongly debated for magnetic shape memory alloys. It has been very recently demonstrated that the modulated martensites in Ni-Mn-Ga are adaptive phases. The results presented here corroborate this theory for the first time, for three different compositions. Moreover, we demonstrate with the help of the adaptive modulations theory that b-variants of the 14-modulated martensite form close to the free surface of the film to release the stress induced by branching of macro-twinned domains during the martensitic transformation on a rigid substrate. At room temperature, the content of such b-variants is found to strongly decrease when the macro-twinned domain sizes increase.
This study focuses on the powder processing methodology (PPM) for the fabrication of metal matrix composite using Graphite flakes (Grf) reinforced Copper (Cu). The manufacturing route involved 1) a reductive treatment of Grf powder to purify and increase its quality, 2) the mixing of the Cu and the Grf (0 to 40 vol.%) powders with a fast and efficient resonant acoustic (RA) mixer, and finally 3) the cold and hot-pressing of composite powders. Comparison of PPM is made with literature and a usual method used in our laboratory. The quality of Grf after different steps was analyzed by Raman spectroscopy and phase compositions and microstructure of the composite materials were analyzed by XRD and SEM, respectively. It was shown that this new PPM demonstrated better composite structural and thermal properties even at low volume fraction of Grf with a maximum of 630 W.m-1 .K-1 obtained with 40 vol.% of Grf at 70 °C. This was possible thanks to our new PPM which allows getting lower defects in the Carbon lattice of Grf and oxygen content in the final composite materials.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.