Search results for "engineering.material"

ELECTRICAL PROPERTIES OF LEAD FERROTANTALATE CERAMICS

2009

ABSTRACT Perovskite structures with high dielectric constants and magnetic properties play an important role in micro- and optoelectronics and have numerous practical applications. Relaxor type ferroelectric ceramics PbFe1/2Ta1/2O3 with perovskite structure was subject of present studies. Pyrochlore free lead ferrotantalate ceramics were produced by solid state technology from oxides. Low- and infra-low frequency studies of dielectric properties of PbFe1/2Ta1/2O3 ceramics have revealed considerable infra-low frequency dispersion at temperatures above the temperature of maximum dielectric permittivity. The observed dispersion described by lemniscates is due to a considerable Maxwell-Wagner r…

Heusler Compounds at a Glance

2013

The class of Heusler compounds, including the XYZ and the X 2 YZ compounds, does not only have an endless number of members, but also a vast variety of properties can be found in this class of materials, ranging from semi-conductors, half-metallic ferromagnets, superconductors, and topological insulators to shape memory alloys. With this chapter, we would like to provide an overview of Heusler compounds, focusing on basis design principles, their properties and potential applications.

Rational design of new materials for spintronics: Co2FeZ (Z=Al, Ga, Si, Ge)

2008

Spintronic is a multidisciplinary field and a new research area. New materials must be found for satisfying the different types of demands. The search for stable half-metallic ferromagnets and ferromagnetic semiconductors with Curie temperatures higher than room temperature is still a challenge for solid state scientists. A general understanding of how structures are related to properties is a necessary prerequisite for material design. Computational simulations are an important tool for a rational design of new materials. The new developments in this new field are reported from the point of view of material scientists. The development of magnetic Heusler compounds specifically designed as …

Quaternary half-metallic Heusler ferromagnets for spintronics applications

2011

This work reports on three quaternary Heusler compounds NiFeMnGa, NiCoMnGa, and CuCoMnGa. In contrast to their ternary relatives, quaternary Heusler compounds are still rarely investigated. A very large pool of interesting materials lies thus idle waiting for exploration. The difficulty consists in choosing prospective compositions, and trial and error is elaborate and expensive. We have identified several candidates employing ab initioelectronic-structure calculations. The compounds were synthesized, and the structural and magnetic properties were investigated experimentally. CuCoMnGa is a quaternary Heusler compound; NiFeMnGa and NiCoMnGa are unreported half-metallic ferromagnetic materia…

Tuning the carrier concentration for thermoelectrical application in the quaternary Heusler compound Co2TiAl(1−x)Six

2010

The family of half-metallic ferromagnets Co2TiZ exhibits exceptional transport properties. The investigated compounds Co2TiAl(1−x)Six (x = 0.25, 0.5, 0.75) show Curie temperatures (TCs) that vary between 250 and 350 K, depending on the composition. Above TC the Seebeck coefficient remains constant. This makes them promising candidates for thermoelectric devices such as thermocouples with a tunable working range. The electrical resistivity data show an anomaly at TC which is attributed to changes in the electronic structure and therefore in the carrier concentration.

61Ni MÖSSBAUER EFFECT STUDIES OF THE FERRIMAGNETIC SPINEL NiCr2O4 IN AN APPLIED MAGNETIC FIELD

1980

Phase separation in the quaternary Heusler compound CoTi(1−x)MnxSb – A reduction in the thermal conductivity for thermoelectric applications

2010

We investigate the phase separation of the solid solution CoTi(1−x)MnxSb into the two Heusler compounds CoTiSb and CoMnSb. Energy-dispersive X-ray spectroscopy measurements on the two-phase material reveal the presence of size- and shape-tunable CoTiSb regions in a CoMnSb matrix. We demonstrate that the formed phase and grain boundaries have a considerable influence on the phonon scattering processes, which leads to a reduction in the thermal conductivity by a factor of three compared to single-phase CoTiSb.

Growth zoning and strain patterns inside diamond crystals as revealed by Raman maps

2005

The Raman mapping technique provides a non-destructive means of studying internal growth textures and other micro-structural heterogeneity inside diamond single-crystals. Raman maps showing distribution patterns of the bandwidth (FWHM) of the main first-order lattice vibration of diamond ( LO=TO phonon at ~1332 cm −1 ) along two-dimensional planes inside diamond crystals may reveal the internal growth zoning of these crystals. The observed zoning is affected, and in some cases even obscured in micro-areas adjacent to inclusions, by patterns of heterogeneous strain in the diamond. We present Raman maps obtained from diamond crystals containing large, single-crystal graphite inclusions, from …

Thin epitaxial films of the Heusler compound

2005

Abstract We prepared thin films of the Heusler compound Co 2 Cr 0.6 Fe 0.4 Al with the B2 structure on a-plane (1 1  2 ¯  0) Al 2 O 3 by sputtering. Films grown at high temperatures ( T ⩾ 600 ∘ C ) on Al 2 O 3 are fully epitaxial with the (1 1 0) and (1  1 ¯  0) planes of the film parallel to the (1 1  2 ¯  0) and (0 0 0 1) planes of the substrate, respectively. These epitaxial films possess a higher surface roughness than films grown at room temperature. The films show nearly rectangular hysteresis loops with coercive fields of the order of 10 mT. Magnetooptical Kerr measurements show an in-plane anisotropy of the magnetization with the easy axis in { 0 0 1 } direction. Hall measurements s…

Comparative study of illite clay and illite-based geopolymer products

2011

Quaternary (Q-clay) clayey deposits are one of the dominating parts of mineral raw materials of the sedimentary cover at present area of Latvia. These clays can be characterised by illite content up to 75-80 %. Two ways for use of illite clays were studied: conventional and geopolymers method. Purpose of the second mentioned method was showing the influence of alkali (KOH) on the transformation of Q-clay/illite structure. Obtained products were investigated by IR–spectroscopy, DTA and XRD, pore size distribution was determined as well. Some ceramic properties and compressive strength were determined and compared. IR-spectrum showed the effect of alkali on the transformation of Q-clay/illite…