Phononic Structure Engineering: the Realization of Einstein Rattling in Calcium Cobaltate for the Suppression of Thermal Conductivity (original) (raw)

Novel K Rattling: A New Route to Thermoelectric Materials?

Journal of Applied Physics

We have performed ab initio molecular dynamics (MD) simulations to study the alkali-metal dynamics in the Al-doped (KAl0.33W1.67O6 and RbAl0.33W1.67O6) and undoped (KW2O6 and RbW2O6) defect pyrochlore tungstates. The K atoms exhibit novel rattling dynamics in both the doped and undoped tungstates while the Rb atoms do not. The KAl0.33W1.67O6 experimental thermal conductivity curve shows an unusual depression between ~ 50 K and ~ 250 K, coinciding with two crossovers in the K dynamics: the first at ~ 50 K, from oscillatory to diffusive, and the second at ~ 250 K, from diffusive back to oscillatory. We show that the origin of these crossovers in the dynamics is the complex reconstruction of the potential around the K atoms as the temperature changes, leading to a hardening of the potential with increasing temperature. This unusual reconstruction of the potential may have important implications for the interpretation of finite-temperature dynamics based on zero-temperature potentials i...

“ Sleeping Phonons and Dancing Electrons : Computational Design of Novel Thermoelectric Materials ”

2016

High performance thermoelectric materials are key to the development of an energy efficient technology. Unfortunately, the design and tailoring of materials for thermoelectric energy conversion is a formidable task. Electrical and heat transport coefficients must satisfy contradictory requirements that depend on the details of the electronic structure, the anharmonic terms in the vibrations, and the effects of chemical disorder and defects. We have exploited the capability of computational methods based on density functional theory to predict the thermoelectric properties of novel chemical compositions. I will discuss heuristic design rules for efficient thermoelectric energy conversion materials as derived from standard electronic structure calculations and also applications to skutterudite and oxide materials. Speaker: Edward Brown Michigan State University September 28, 2009 “Journey to the Core of a Neutron Star” Abstract: Neutron stars are composed of the densest observable mat...

Electronic Texture of the Thermoelectric Oxide Na0.75CoO2

Physical Review Letters, 2008

From 59Co and 23Na NMR, we demonstrate the impact of the Na+ vacancy ordering on the cobalt electronic states in Na0.75CoO2: at long time scales, there is neither a disproportionation into 75 % Co3+ and 25 % Co4+ states, nor a mixed-valence metal with a uniform Co3.25+ state. Instead, the system adopts an intermediate configuration in which 30 % of the lattice sites form an ordered pattern of localized Co3+ states. Above 180 K, an anomalous mobility of specific Na+ sites is found to coexist with this electronic texture, suggesting that the formation of the latter may contribute to stabilizing the Na+ ordering. Control of the ion doping in these materials thus appears to be crucial for fine-tuning of their thermoelectric properties.