Paz Vaqueiro

Bio: Paz Vaqueiro is an academic researcher from University of Reading. The author has contributed to research in topics: Thermoelectric effect & Thermoelectric materials. The author has an hindex of 34, co-authored 131 publications receiving 3036 citations. Previous affiliations of Paz Vaqueiro include Heriot-Watt University & University of Santiago de Compostela.

Recent developments in nanostructured materials for high-performance thermoelectrics

Abstract: This highlight discusses recent trends in the search for new high-efficiency thermoelectric materials. Thermoelectric materials offer considerable attractions in the pursuit of a more efficient use of existing energy resources, as they may be used to construct power-generation devices that allow useful electrical power to be extracted from otherwise waste heat. Here, we focus on the significant enhancements in thermoelectric performance that have been achieved through nanostructuring. The principal factor behind the improved performance appears to be increased phonon scattering at interfaces. This results in a substantial reduction in the lattice contribution to thermal conductivity, a low value of which is a key requirement for improved thermoelectric performance.

Influence of Complexing Agents and pH on Yttrium−Iron Garnet Synthesized by the Sol−Gel Method

Abstract: A systematic study of the sol−gel technique for the synthesis of Y3Fe5O12 is presented, using two different complexing agents (citric acid and malonic acid) and adding two different alcohols (ethylene glycol and glycerol). The influence of the pH value of the initial solution on the final product is also studied. Yttrium−iron garnet YIG is obtained from the gels by heating above 650 °C in air atmosphere. Samples are characterized by X-ray powder diffraction and IR spectroscopy. The crystallite size and the lattice parameter are also determined, and their dependence on the synthesis conditions is studied.

Structure and magnetism in synthetic pyrrhotite Fe 7 S 8 : A powder neutron-diffraction study

Abstract: The relationship between structural and magnetic properties in stoichiometric pyrrhotite ${\text{Fe}}_{7}{\mathrm{S}}_{8}$ has been investigated using variable-temperature neutron-diffraction data. Below its magnetic ordering temperature, ${T}_{\mathrm{N}}=598(5)\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, ${\text{Fe}}_{7}{\mathrm{S}}_{8}$ exhibits a monoclinic 4C structure, related to that of NiAs, in which fully occupied cation layers alternate with cation-deficient layers. The magnetic structure consists of ferromagnetically aligned layers, with antiferromagnetic coupling of adjacent layers. The ordered moment of $3.16(1){\ensuremath{\mu}}_{\mathrm{B}}$ at $11\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ is directed at an angle of $29\ifmmode^\circ\else\textdegree\fi{}$ to the layers. The magnetic transition is accompanied by a structural transformation from the monoclinic 4C structure to a hexagonal cation-deficient NiAs structure, in which the vacancies are statistically distributed between all layers. Although the 4C structure is recovered on cooling through the magnetic transition, the resultant phase exhibits a significant degree of intralayer cation disorder.

Ferromagnetic materials

Abstract: In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Recent advances in the liquid-phase syntheses of inorganic nanoparticles.

Abstract: The development of novel materials is a fundamental focal point of chemical research; and this interest is mandated by advancements in all areas of industry and technology. A good example of the synergism between scientific discovery and technological development is the electronics industry, where discoveries of new semiconducting materials resulted in the evolution from vacuum tubes to diodes and transistors, and eventually to miniature chips. The progression of this technology led to the development * To whom correspondence should be addressed. B.L.C.: (504) 2801385 (phone); (504) 280-3185 (fax); bcushing@uno.edu (e-mail). C.J.O.: (504)280-6846(phone);(504)280-3185(fax);coconnor@uno.edu (e-mail). 3893 Chem. Rev. 2004, 104, 3893−3946

The evolution of 'sol-gel' chemistry as a technique for materials synthesis

Abstract: From its initial use to describe hydrolysis and condensation processes, the term ‘sol–gel’ is now used for a diverse range of chemistries. In fact, it is perhaps better defined more broadly as covering the synthesis of solid materials such as metal oxides from solution-state precursors. These can include metal alkoxides that crosslink to form metal–oxane gels, but also metal ion–chelate complexes or organic polymer gels containing metal species. What is important across all of these examples is how the choice of precursor can have a significant impact on the structure and composition of the solid product. In this review, we will attempt to classify different types of sol–gel precursor and how these can influence a sol–gel process, from self-assembly and ordering in the initial solution, to phase separation during the gelation process and finally to crystallographic transformations at high temperature.

The panoscopic approach to high performance thermoelectrics

Abstract: This review discusses recent developments and current research in high performance bulk thermoelectric materials, comprising nanostructuring, mesostructuring, band alignment, band engineering and synergistically defining key strategies for boosting the thermoelectric performance. To date, the dramatic enhancements in the figure of merit achieved in bulk thermoelectric materials have come either from the reduction in lattice thermal conductivity or improvement in power factors, or both of them. Here, we summarize these relationships between very large reduction of the lattice thermal conductivity with all-scale hierarchical architecturing, large enhanced Seebeck coefficients with intra-matrix electronic structure engineering, and control of the carrier mobility with matrix/inclusion band alignment, which enhance the power factor and reduce the lattice thermal conductivity. The new concept of hierarchical compositionally alloyed nanostructures to achieve these effects is presented. Systems based on PbTe, PbSe and PbS in which spectacular advances have been demonstrated are given particular emphasis. A discussion of future possible strategies is aimed at enhancing the thermoelectric figure of merit of these materials.