Thermoelectric properties of PbTe-based materials driven near the ferroelectric phase transition from first principles

Murphy, Aoife Rose

Thermoelectric properties of PbTe-based materials driven near the ferroelectric phase transition from first principles

dc.check.opt-out	No	en
dc.check.reason	This thesis is due for publication or the author is actively seeking to publish this material	en
dc.contributor.advisor	Savic, Ivana	en
dc.contributor.advisor	Fahy, Stephen B.	en
dc.contributor.author	Murphy, Aoife Rose
dc.contributor.funder	Science Foundation Ireland	en
dc.date.accessioned	2018-04-27T10:23:06Z
dc.date.issued	2017
dc.date.submitted	2017
dc.description.abstract	The thermoelectric figure of merit, ZT, is a dimensionless parameter used to characterise the efficiency of a thermoelectric material. One of the most common techniques to improve ZT is to suppress lattice thermal conductivity via nanostructuring. However, this approach often comes with the cost of reduced electrical conductivity and Seebeck coefficient, resulting in only modest increases to ZT. Using the first principles Boltzmann transport framework, we show that driving PbTe-based materials to the verge of the soft mode (ferroelectric) phase transition could be a powerful strategy to reduce their lattice thermal conductivity while potentially preserving the electrical properties beneficial for a large ZT. The proposed concept is based on the induction of considerably softened zone-centre transverse optical modes, increasing their anharmonic coupling with low-frequency heatcarrying acoustic phonons and reducing phonon lifetimes at all frequencies. We illustrate this concept by applying biaxial tensile (001) strain to PbTe and its alloys with PbSe; and by alloying PbTe with a rhombohedral material, GeTe, reducing the lattice thermal conductivity by a factor of 2−3 compared to PbTe. Furthermore, by tuning the chemical composition of Pb1−xGexTe alloys, we also investigate the roles of proximity to the phase transition, mass disorder, and phase of the alloy in reducing the lattice thermal conductivity. Finally, we take the first steps towards a fully ab initio calculation of the figure of merit of PbTe-based materials near the phase transition by considering electron-phonon interactions, and find fair agreement between the calculated electronic mobility of PbTe and experiment. Due to certain symmetry forbidden electron-phonon coupling, we anticipate that our outlined approach may not degrade electronic properties beneficial for a large ZT. This proposed concept is general and offers a promising new strategy to potentially increase thermoelectric efficiency.	en
dc.description.sponsorship	SFI Starting Investigator Research Grant No. 11/SIRG/E2113	en
dc.description.status	Not peer reviewed	en
dc.description.version	Accepted Version
dc.format.mimetype	application/pdf	en
dc.identifier.citation	Murphy, A. R. 2017. Thermoelectric properties of PbTe-based materials driven near the ferroelectric phase transition from first principles. PhD Thesis, University College Cork.	en
dc.identifier.endpage	171	en
dc.identifier.uri	https://hdl.handle.net/10468/5893
dc.language.iso	en	en
dc.publisher	University College Cork	en
dc.rights	© 2017, Aoife Rose Murphy.	en
dc.rights.uri	http://creativecommons.org/licenses/by-nc-nd/3.0/	en
dc.subject	Thermoelectric materials	en
dc.subject	Phase transition	en
dc.subject	Ferroelectric	en
dc.subject	Soft mode	en
dc.subject	Thermal conductivity	en
dc.subject	Seebeck coefficient	en
dc.subject	Electrical conductivity	en
dc.subject	Thermoelectric figure of merit	en
dc.subject	Phonon lifetimes	en
dc.subject	Phonon scattering	en
dc.subject	Electron phonon coupling	en
dc.subject	Electronic mobility	en
dc.subject	DFT	en
dc.subject	DFPT	en
dc.subject	Relaxation time approximation	en
dc.subject	BTE RTA	en
dc.subject	PbTe	en
dc.subject	GeTe	en
dc.subject	Anharmonicity	en
dc.subject	Lattice thermal conductivity	en
dc.subject	Electron phonon	en
dc.subject	Soft optical modes	en
dc.subject	Soft zone centre optical modes	en
dc.subject	Anharmonic phonon coupling	en
dc.subject	Electronic lifetimes	en
dc.subject	Lifetimes	en
dc.subject	Broadband phonon scattering	en
dc.subject	Tensile strain	en
dc.subject	Alloy	en
dc.subject	Resonant bonding	en
dc.subject	Density functional theory	en
dc.subject	Density functional perturbation theory	en
dc.subject	Boltzmann transport equation	en
dc.thesis.opt-out	false
dc.title	Thermoelectric properties of PbTe-based materials driven near the ferroelectric phase transition from first principles	en
dc.type	Doctoral thesis	en
dc.type.qualificationlevel	Doctoral	en
dc.type.qualificationname	PhD	en
ucc.workflow.supervisor	ivana.savic@tyndall.ie