Exploring Packaging Strategies of Nano-embedded Thermoelectric Generators

Embedding nanostructures within a bulk matrix is an important practical approach towards the electronic engineering of high performance thermoelectric systems. For power generation applications, it ideally combines the efficiency benefit offered by low dimensional systems along with the high power output advantage offered by bulk systems. In this work, we uncover a few crucial details about how to embed nanowires and nanoflakes in a bulk matrix so that an overall advantage over pure bulk may be achieved. First and foremost, we point out that a performance degradation with respect to bulk is inevitable as the nanostructure transitions to being multi moded. It is then shown that a nano embedded system of suitable cross-section offers a power density advantage over a wide range of efficiencies at higher packing fractions, and this range gradually narrows down to the high efficiency regime, as the packing fraction is reduced. Finally, we introduce a metric - \emph{the advantage factor}, to elucidate quantitatively, the enhancement in the power density offered via nano-embedding at a given efficiency. In the end, we explore the maximum effective width of nano-embedding which serves as a reference in designing generators in the efficiency range of interest.Comment: 10 pages, 8 figure

Layer-dependent electronic structures and magnetic ground states of polar-polar LaVO3/KTaO3\rm{LaVO_3/KTaO_3} (001) interfaces

Using first-principles and model Hamiltonian approach, we explore the electronic properties of polar-polar LaVO$_3$/KTaO$_3$ (LVO/KTO, 001) hetero-interfaces of up to six and five layers of KTO and LVO, respectively. Our calculations suggest the presence of multiple Lifshitz transitions (LT) in the $t_{2g}$ bands which may show up in high thermal conductivity and Seebeck coefficient. The LT can be tuned by the number of LaVO$_3$ layers or gate voltage. The spin-orbit coupling is found to be negligible, coming only from the Ta $5d_{xy}$-derived band, 5$d_{xz}$ and 5$d_{yz}$ bands being far away from the Fermi level. The magnetic properties of the interfaces, due to Vanadium ions, turn out to be intriguing. The magnetic states are highly sensitive to the number of layers of LaVO$_3$ and KTaO$_3$: the interfaces with equal number of LVO and KTO layers always favor an antiferromagnetic (AFM) ordering. Moreover, the combination of even-even and odd-odd layers shows an AFM order for more than two LaVO$_3$ layers. The spin-polarized density of states reveals that all the interfaces with ferromagnetic (FM) ground states are \textit{half-metallic}. The small energy differences between AFM and FM configurations indicate a possible coexistence of competing AFM and FM ground states in these interfaces. In addition, the interface requires different number of LVO layers for it to be metallic: half-metallic FM for three and above, and metallic AFM for four and above.Comment: 11 pages, 10 figure