Spatially resolved measurements of thermal transport in ferroelectric materials using scanning thermal microscopy

Abstract

This thesis focuses on the investigation of spatial variations in thermal conductivity linked to domain wall microstructure in ferroelectric lithium niobate. This necessitated development of a measurement protocol based on microscopic temperature sensing using Scanning Thermal Microscopy (SThM). The adopted method involved periodically Joule heating the sample of interest using a deposited thin metal bar transducer in conjunction with lock-in detection of the induced surface temperature oscillations by SThM. Spatial variations in surface temperature recorded across the uniformly Joule-heated bar were then interpreted as resulting from microstructure-related variations in the thermal conductivity of the underlying sample.

Initially, a proof-of-principle imaging experiment was conducted, revealing thermal differences between alternating metal and ceramic strips in a commercial multilayer ceramic capacitor. The sample exhibited a thermal response resembling an effective medium, with additional localised contrast features corresponding to the spatial distribution of thermal conductivity. This interpretation was further validated through COMSOL modelling.

To investigate the possibility of enhanced thermal transport along electrically conducting domain wall, an Atomic Force Microscopy poling procedure was employed to create regular arrays of charged conducting domain walls in lithium niobate. Following this, SThM based thermal transport measurements were carried out and the temperature profile measured across the transducer served as initial evidence for enhanced domain wall thermal transport. Post-processing of the raw SThM data focussed on identifying and eliminating any erroneous temperature signals, however, signal-to-noise issues made it challenging to confidently isolate the contributions of domain walls.

Thesis is embargoed until 31 December 2028.

Date of Award	Dec 2023
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Engineering & Physical Sciences Research Council & Science Foundation Ireland
Supervisor	Raymond McQuaid (Supervisor)