Prospects for Engineering Thermoelectric Properties in La_1/3NbO₃ Ceramics Revealed via Atomic-Level Characterization and Modeling

Abstract

A combination of experimental and computational techniques has been employed to explore the crystal structure and thermoelectric properties of A-site-deficient perovskite LaNbO ceramics. Crystallographic data from X-ray and electron diffraction confirmed that the room temperature structure is orthorhombic with Cmmm as a space group. Atomically resolved imaging and analysis showed that there are two distinct A sites: one is occupied with La and vacancies, and the second site is fully unoccupied. The diffuse superstructure reflections observed through diffraction techniques are shown to originate from La vacancy ordering. LaNbO ceramics sintered in air showed promising high-temperature thermoelectric properties with a high Seebeck coefficient of S = -650 to -700 μV/K and a low and temperature-stable thermal conductivity of k = 2-2.2 W/m·K in the temperature range of 300-1000 K. First-principles electronic structure calculations are used to link the temperature dependence of the Seebeck coefficient measured experimentally to the evolution of the density of states with temperature and indicate possible avenues for further optimization through electron doping and control of the A-site occupancies. Moreover, lattice thermal conductivity calculations give insights into the dependence of the thermal conductivity on specific crystallographic directions of the material, which could be exploited via nanostructuring to create high-efficiency compound thermoelectrics.

Enhancing the thermoelectric properties of Sr 1− x Pr 2 x /3 □ x /3 TiO 3± δ through control of crystal structure and microstructure

“…For example, κ total varied between 6.5 and 4 W m −1 K −1 for samples with x = 0.10, while it was almost constant at approximately 2 W m −1 K −1 for samples of x = 1.0. This temperature independence of κ total has also been reported for other A-site deficient perovskites such as, La 1/3 NbO 3 [48], Nd 2/3 TiO 3 [49,50] and Sr 1−x La 2x/3 x/3 TiO 3 [12,14]. As the microstructural features in the present investigation (figure 2) are all much larger than the phonon mean-free path (l ph ) for SrTiO 3 (less than 10 nm) [7,51], the temperature dependence of κ total cannot be linked to simple bulk microstructural effects, but can be explained by changes in crystal structure and specifically changes in lattice thermal conductivity (κ lattice ).…”

The impact of tilt grain boundaries on the thermal transport in perovskite SrTiO3layered nanostructures. A computational study

“…Finally our configurations can be thought as air sintered samples where the amount of oxygen vacancies will decrease dramatically. 50,51 All simulated systems (i.e. layered nanostructures) contain two identical grain boundaries with the X direction perpendicular to the YZ boundary plane.…”

High Spatial and Energy Resolution Analytical Scanning Transmission Electron Microscopy for Quantum Materials

“…The calculations are provided at various temperatures, using a rigid-band model that assumes no shape change in the band structure, but only a shift in the Fermi energy due to the changing electron doping concentration. [5]…”