Final Report Summary - 2DTHERMS (Design of new thermoelectric devices based on layered and field modulated nanostructures of strongly correlated electron systems)
Thermoelectric materials are able to convert temperature differences into electric voltages, and vice versa. The efficiency of this conversion is limited by intrinsic characteristics of the material itself, mainly its thermal and electrical conductivity. The original motivation of this project was the exploration of new roads toward more efficient thermoelectric materials, beyond the classical compositions of post-transition-metal alloys. Particularly, we proposed that nanostructured strongly correlated electron systems (mainly transition-metal oxides and nitrides) could be a good place to look for these requirements. The initial hypothesis was based on the strong coupling between the electronic, lattice and magnetic degrees of freedom, which could be used to tune thermal and electrical conductivity, independently.
During the course of this project we demonstrate a new way to tune independently the thermoelectric power and electrical conductivity in polaronic and itinerant materials by epitaxial strain, and defect management during growth. This was exemplified in La2NiO4 and Nb:SrTiO3 [1].
On the other hand, we showed that intrinsic lattice instabilities can suppress thermal conductivity in transition-metal nitrides, particularly in CrN. We synthesized thin-films of this material and showed that this effect can be exploited to dramatically enhance its thermoelectric performance [2]. We hypothesize that this is the result of strong bond-length fluctuations induced by the proximity of this material to the itinerant electron limit. We believe this strategy of tuning a semiconductor system to the itinerant electron side could be useful for the design of new thermoelectric materials, not only by the effect in the electronic properties, but also because of the reduction in the thermal conductivity.
Finally, we optimized a simple and affordable chemical solution method to synthesize high quality epitaxial thin-films of most of the oxides prepared in this project. We have shown that epitaxial heterostructures, with an excellent control over the stoichiometry and thickness can be produced by this simple chemical method [3]; which constitutes one of the most interesting and influential advances of this project.
[1] P. Bach et al. “Strain-induced enhancement of the thermoelectric power in thin films of hole-doped La2NiO4+d"
APL MATERIALS VOL 1, 021101, 2013.
A. Sarantopoulos, et al. "Electron degeneracy and intrinsic magnetic properties of epitaxial Nb:SrTiO3
thin-films controlled by defects"
PHYSICAL REVIEW LETTERS, 115, 166801, 2015.
[2] C. X. Gonzalez-Quintela, et al. "Epitaxial CrN thin-films with thermoelectric high figure of merit"
ADVANCED MATERIALS, VOL 27, 3032, 2015.
[3] Jose Manuel Vila-Fungueiriño, et al."Room-Temperature Ferromagnetism in Thin Films of LaMnO3 Deposited by a Chemical Method Over Large Areas"
ACS APPLIED MATERIALS AND INTERFACES VOL 7, 5410, 2015.
B. Rivas-murias, et al. "High quality epitaxial thin films of misfit cobalt oxides synthesized by a chemical solution method"
Scientific Reports, VOL 5, 11889, 2015.
During the course of this project we demonstrate a new way to tune independently the thermoelectric power and electrical conductivity in polaronic and itinerant materials by epitaxial strain, and defect management during growth. This was exemplified in La2NiO4 and Nb:SrTiO3 [1].
On the other hand, we showed that intrinsic lattice instabilities can suppress thermal conductivity in transition-metal nitrides, particularly in CrN. We synthesized thin-films of this material and showed that this effect can be exploited to dramatically enhance its thermoelectric performance [2]. We hypothesize that this is the result of strong bond-length fluctuations induced by the proximity of this material to the itinerant electron limit. We believe this strategy of tuning a semiconductor system to the itinerant electron side could be useful for the design of new thermoelectric materials, not only by the effect in the electronic properties, but also because of the reduction in the thermal conductivity.
Finally, we optimized a simple and affordable chemical solution method to synthesize high quality epitaxial thin-films of most of the oxides prepared in this project. We have shown that epitaxial heterostructures, with an excellent control over the stoichiometry and thickness can be produced by this simple chemical method [3]; which constitutes one of the most interesting and influential advances of this project.
[1] P. Bach et al. “Strain-induced enhancement of the thermoelectric power in thin films of hole-doped La2NiO4+d"
APL MATERIALS VOL 1, 021101, 2013.
A. Sarantopoulos, et al. "Electron degeneracy and intrinsic magnetic properties of epitaxial Nb:SrTiO3
thin-films controlled by defects"
PHYSICAL REVIEW LETTERS, 115, 166801, 2015.
[2] C. X. Gonzalez-Quintela, et al. "Epitaxial CrN thin-films with thermoelectric high figure of merit"
ADVANCED MATERIALS, VOL 27, 3032, 2015.
[3] Jose Manuel Vila-Fungueiriño, et al."Room-Temperature Ferromagnetism in Thin Films of LaMnO3 Deposited by a Chemical Method Over Large Areas"
ACS APPLIED MATERIALS AND INTERFACES VOL 7, 5410, 2015.
B. Rivas-murias, et al. "High quality epitaxial thin films of misfit cobalt oxides synthesized by a chemical solution method"
Scientific Reports, VOL 5, 11889, 2015.