First-principles calculation of thermal transport properties driven by the ferro- and antiferroelectric phase transition : A comprehensive study for ABC structures

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Kemian tekniikan korkeakoulu | Master's thesis
Advanced Materials for Innovation and Sustainability
Degree programme
Master's Programme in Chemical and Material Science
Previous research expected the ABC (G1-G2-G15) compounds to have similar ferroelectricity with perovskite compounds, but there is a lack of research about their thermal transport properties, which are essential for practical application. Based on the Density Functional Theory (DFT), their lattice thermal conductivities (kappaL) are calculated in this study by using the Self-Consistent Phonon Method (SCP) combined with the Compressive Sensing (CS) approach. Using LiBeP, NaMgBi, NaMgP, and LiMgP as target examples, their structural, electronic, and thermal transport properties changes between ferro- and anti-ferroelectric phase transitions are calculated. The anti-ferroelectric to the ferroelectric phase transition increases the bulk kappaL of LiBeP and NaMgBi by 53% and 17% at 300 K, respectively. By contrast, the bulk kappaL of NaMgP exhibits a decreasing rate of 42%. Among the four materials in the polar phase, their bulk kappaL order from highest to lowest is LiBeP, LiMgP, NaMgP, and NaMgBi. Remarkably, the bulk kappaL of polar LiBeP (25.5 W/mK) is 5 times larger than the rest three materials in polar phases (around 4.9 W/mK). With temperature increasing from 250 to 900 K, the bulk kappaL of LiBeP, NaMgBi, and LiMgP are reduced by 68%, 64% and 55%, respectively. From 250 to 450 K caused by a different converged range, it of NaMgP decreases 57%. Moreover, the comparison of the harmonic and anharmonic methods indicates that the anharmonic method hosts higher physical rationality for ABC compounds. By analyzing the structural parameters, mode-level properties (phonon lifetime, group velocity, Grüneisen parameter), and electronic properties (band structure, electron localization function), the reasons for the kappaL change under different phases and temperatures are explained with details in terms of anisotropy, anharmonicity, scattering, and covalent bonding.
Karttunen, Antti
Thesis advisor
Shen, Chen
ferroelectric, density functional theory, anharmonicity, thermal transport properties
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