Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Mysterious SiB3: Identifying the relation between a- and b-SiB3
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).ORCID iD: 0000-0002-6886-2649
(English)Manuscript (preprint) (Other academic)
National Category
Inorganic Chemistry
Research subject
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:su:diva-167786OAI: oai:DiVA.org:su-167786DiVA, id: diva2:1302151
Available from: 2019-04-03 Created: 2019-04-03 Last updated: 2019-04-05Bibliographically approved
In thesis
1. Structure-property investigation of ZnSb, ZnAs, and SiB3: - binary semiconductors with electron poor framework structures
Open this publication in new window or tab >>Structure-property investigation of ZnSb, ZnAs, and SiB3: - binary semiconductors with electron poor framework structures
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In today’s society, where energy conservation and green energy are buzz words, new scientific discoveries in green energy harvesting is key. This work focuses on materials capable of recycling low value thermal energy. Low value thermal energy, waste heat, is for free, and can be transformed into valuable electricity via thermoelectric technology. A thermoelectric device cleanly converts heat into electricity through the Seebeck effect. Thermoelectric devices can play an important role in satisfying the future global need for efficient energy management, however, the primary barrier of improving thermoelectric devices is the materials themselves.

The aim of this thesis is to identify new compositions and structures for thermoelectric materials. In particular, the concept of “electron poor framework semiconductors” is explored. Electron Poor Framework Semiconductors (EPFS) are materials at the border between metals and non-metals, which often show intricate and unique structures with complex bonding schemes. Generally, constituting elements should be from group 12(II) (Zn, Cd), 13(III) (B, Al, Ga, In), 14(IV) (Si, Ge, Sn, Pb), 15(V) (Sb, Bi), and 16(VI) (Te), i.e. elements which have a similar electronegativity (between 1.5-2.0). All EPFS materials have in common highly complex crystal structures, which are thought to be a consequence of their electron-poor bonding patterns. EPFS materials have an intrinsically very low – glass like - lattice thermal conductivity. The focus of this thesis is on combinations of group 12(II) (Zn) with 16 (V) (As, Sb), and 13(III) (B) with 14(IV) (Si).

ZnSb possesses a simple structure with 8 formula units in an orthorhombic unit cell, it is considered a stoichiometric compound without noticeable structural disorder. In this thesis ZnSb is used as a model system to establish more broadly structure–property correlations in Sb based EPFS materials.

ZnSb was established to possess an impurity band that determines electrical transport properties up to 300–400 K. Doping of ZnSb with Ag seems to enhance the impurity band by increasing the number of acceptor states and improving charge carrier density by two orders of magnitude. ZT values of Ag doped ZnSb are found to exceed 1 at 350 K. The origin of the low thermal conductivity of ZnSb was traced back to a multitude of localized low energy optic modes, acting as Einstein-like rattling modes.

ZnAs was accessed through high pressure synthesis. The compound is isostructural to ZnSb and possess an indirect band gap of 0.9 eV, which is larger than that for ZnSb (0.5 eV). The larger band gap is attributed to the higher polarity of Zn-As bonds. The electrical resistivity of ZnAs is higher and the Seebeck coefficient is lower compared to ZnSb. However, ZnAs and ZnSb exhibit similarly low lattice thermal conductivity, although As is considerably lighter than Sb. This was explained by their similar bonding properties.

Lastly, the longstanding mystery of SiB3 phases was resolved. The formation of metastable and disordered α-SiB3-x is fast and thus kinetically driven, whereas formation of stable β-SiB3 is slow and not quantitative unless high pressure conditions are applied. This thesis work established reproducible synthesis routes for both materials. The fast kinetics can be exploited for simultaneous synthesis and sintering of α -SiB3-x specimens in a SPS device. It is suggested that α -SiB3-x represents a promising refractory thermoelectric material.

Place, publisher, year, edition, pages
Stockholm: Department of Materials and Environmental Chemistry (MMK), Stockholm University, 2019. p. 114
Keywords
Thermoelectric, Waste heat harvesting, Semiconductor, X-ray powder diffraction, SEM, Electron poor framework, EPFS, Green house effect
National Category
Inorganic Chemistry
Research subject
Inorganic Chemistry
Identifiers
urn:nbn:se:su:diva-167789 (URN)978-91-7797-700-1 (ISBN)978-91-7797-701-8 (ISBN)
Public defence
2019-05-24, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.

Available from: 2019-04-29 Created: 2019-04-03 Last updated: 2019-04-17Bibliographically approved

Open Access in DiVA

No full text in DiVA

Search in DiVA

By author/editor
Eklöf, Daniel
By organisation
Department of Materials and Environmental Chemistry (MMK)
Inorganic Chemistry

Search outside of DiVA

GoogleGoogle Scholar

urn-nbn

Altmetric score

urn-nbn
Total: 45 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf