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Structural Diversity of Ternary and Quaternary Alkali-Metal Pnictides Open Access


Other title
Zintl Phase
Type of item
Degree grantor
University of Alberta
Author or creator
Khatun, Mansura
Supervisor and department
Mar, Arthur (Department of Chemistry)
Examining committee member and department
Grosvenor, Andrew, P. (Department of Chemistry)
Klobukowski, Mariusz (Department of Chemistry)
Lundgren, Rylan (Department of Chemistry)
Rivard, Eric (Department of Chemistry)
Department of Chemistry

Date accepted
Graduation date
2017-11:Fall 2017
Doctor of Philosophy
Degree level
To evaluate the applicability and expand the limit of the Zintl-Klemm concept, many new alkali-metal pnictides were synthesized by high temperature solid reactions in A-M-Pn or A-Tt-Pn ternary systems and A-M-Tt-Pn quaternary systems (A = Na, K, Rb; M = Mn, Zn, Cd; Tt = Si, Ge, Sn; Pn = As, Sb). Their crystal structures were characterized by X-ray diffraction methods. Their electronic structures and bonding interactions were determined using TB-LMTO calculations. Ternary pnictides adopt their own-type structures, having unique structural patterns: corrugated chains (Rb4Zn7As7- and Rb7Mn12Sb12-type structure) and layers (KSn3As3-type structure), GeAs-type layers (NaGe6As6), and 3D-networks (K2Zn5As4). The quaternary AM1.5Tt0.5As2 pnictides prefer to crystallize either in the CaAl2Si2- or ThCr2Si2-type structure, depending on the relative sizes of atoms, as expressed through a structure map. The structure map also suggested that ACd1.5Ge0.5As2 (A = K, Rb) phases would not form; indeed, attempts to prepare them gave new triclinic phases ACdGeAs2 instead. Band structure calculations revealed electronic structures in good agreement with expectations: K2Zn5As4 (0.4 eV), KGe3As3 (0.71 eV), and KCdGeAs2 (0.80 eV) are small band-gap semiconductors; NaZn1.5Si0.5As2 (small overlap at Fermi level) is a semimetal; Rb4Zn7As7 (small gap above Fermi level), Rb7Mn12Sb12 (pseudogap above Fermi level), and NaGe6As6 (small gap below Fermi level) are metallic. Pnictides that have A-to-Pn ratio of 1:2 to 1:3 follow the Zintl concept. Rb4Zn7As7 and Rb7Mn12Sb12 are electron-deficient Zintl phases having an A-to-Pn ratio of ˂2 whereas NaGe6As6 is an electron-rich Zintl phase having an A-to-Pn ratio of ˃3. This work opens a new window to study substitutional chemistry.
This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for the purpose of private, scholarly or scientific research. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.
Citation for previous publication
Stoyko, S. S.; Khatun, M.; Mar, A. Inorg. Chem. 2012, 51, 9517‒9521.Khatun, M.; Stoyko, S. S.; Mar, A. Inorg. Chem. 2013, 52, 12682‒12690.Khatun, M.; Stoyko, S. S.; Mar, A. J. Solid State Chem. 2016, 238, 229‒235.Khatun, M.; Mar, A. Z. Naturforsch., B 2016, 71, 375‒380.Khatun, M.; Stoyko, S. S.; Mar, A. Inorg. Chem. 2013, 52, 3148‒3158.Khatun, M.; Stoyko, S. S.; Mar, A. Inorg. Chem. 2014, 53, 7756‒7762.

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